**NTIA Special Publication 94-30**

**A Technical Report to the Secretary of Transportation**

**on a National Approach to**

**Augmented GPS Services**

![](media/image1.wmf){width="1.9715277777777778in"
height="1.7152777777777777in"}

**U.S. DEPARTMENT OF COMMERCE**

**Ronald H. Brown, Secretary**

**Larry Irving, Assistant Secretary**

**for Communications and Information, and**

**Administrator, National Telecommunications**

**and Information Administration**

**December 1994**

**Study Team**

**Institute for Telecommunication Sciences**

Robert O. DeBolt

Ronald L. Ketchum

Roger A. Dalke

George A. Hufford

Michael Terada

Wayne R. Rust

**U.S. Army Topographic Engineering Center**

Sally L. Frodge

Frederick M. Gloeckler

Robert G. Mann

Thomas M. Cox

Daniel C. Oimoen

James C. Eichholz

**Volpe National Transportation Systems Center**

Elisabeth J. Carpenter

**Overlook Systems Technologies, Inc.**

John H. Martel

Jeffrey A. Johnson

**PREFACE**

This report is provided by the Institute for Telecommunication Sciences
(ITS), National Telecommunications and Information Administration
(NTIA), U.S. Department of Commerce (DOC), to the Federal Highway
Administration (FHWA), U.S. Department of Transportation (DOT), in
fulfillment of Interagency Agreement Number DTFH61-93-Y-00110. Personnel
from ITS, the U.S. Army Topographic Engineering Center, the Volpe
National Transportation Systems Center, and Overlook Systems
Technologies, Inc. contributed to the writing of the report.

The recommendations contained herein are those of the authors, and
should not be construed as official policy of DOT or FHWA. This document
does not convey official policy of DOC, NTIA, or ITS.

Management, administration, and technical monitoring of this Agreement
have been provided by Mr. James A. Arnold, Electronics Engineer, FHWA,
and Mr. Peter A. Serini, Program Analyst, Office of the Secretary (OST),
DOT. Additional oversight was provided by a Study Review Board
representing OST, FHWA, DOT\'s Research and Special Programs
Administration, the Federal Aviation Administration, the Department of
Defense, the National Oceanic and Atmospheric Administration, and the
U.S. Coast Guard.

**ACKNOWLEDGMENTS**

Many individuals provided information and suggestions that were helpful
in the preparation of this report. The authors would especially like to
thank the following:

**Department of Commerce**

Dr. Benjamin W. Remondi (NOAA/NGS)

William E. Strange (NOAA/NGS)

**Department of Defense**

Jules McNeff

Major Joseph Lortie

**Federal Aviation Administration**

Michael Shaw

Paul Drouilhet

Kan Sandhoo (MITRE Corp.)

**U.S. Coast Guard**

Commander Douglas Alsip

James Radice

Captain John Weseman

**Department of Transportation**

George Wiggers (OST)

Heywood Shirer (RSPA)

Frank Mammano (FHWA)

Richard Shamberger (FRA)

**Overlook Systems Technologies, Inc.**

Ed Stephenson

Michael Sorrentino

**Volpe National**

**Transportation Systems Center**

George Webber

Robert Dorer

Ike Tingos

Anya Carroll

John O\'Donnell

Gary Ritter

**Study Review Board**

Joseph F. Canny, Chairman (OST)

Richard Arnold (FAA)

Marty Pozesky (FAA)

R.Adm. J. Austin Yeager (NOAA)

Dr. C. S. Shih (DOT/RSPA)

Dennis C. Judycki (DOT/FHWA)

Richard G. Howe (DOD)

R.Adm. William J. Ecker (USCG)

R.Adm. Gregory A. Pennington (USCG)

**CONTENTS**

Page

LIST OF FIGURES ix

LIST OF TABLES x

EXECUTIVE SUMMARY xi

ABSTRACT 1

1\. INTRODUCTION 3

1.1 Objective 3

1.2 Scope 4

1.3 Study Participants 4

1.4 Study Tasks 4

1.5 Study Approach 5

2\. FEDERAL USER REQUIREMENTS FOR NAVIGATION AND POSITIONING 7

2.1 Land Transportation Requirements 8

2.2 Marine Transportation Requirements 10

2.3 Air Transportation Requirements 11

2.4 Space Transportation Requirements 12

2.5 Non-Transportation Requirements 13

2.6 Requirements Summary 15

3\. DESCRIPTION OF GPS AND AUGMENTED GPS SYSTEMS 17

3.1 GPS Standard Positioning Service and Precise Positioning Service 17

3.2 The Need for Augmentation 17

3.3 Functional Descriptions of Augmented GPS Systems 19

3.3.1 USCG LF/MF Radiobeacon System 22

3.3.2 USCG LF/MF Radiobeacon System Expanded 25

3.3.3 Commercial FM Subcarrier System 27

3.3.4 Wide Area System 1 29

3.3.5 Wide Area System 2 32

3.3.6 Wide Area System 3 35

3.3.7 Wide Area System 4 36

3.3.8 Wide Area System 5 37

3.3.9 Wide Area System 6 38

3.3.10 Continuously Operating Reference Station System 39

3.3.11 Loran-C System 40

4\. EVALUATION OF AUGMENTED GPS SYSTEMS 43

4.1 System Technical Capabilities 44

4.2 Capabilities Versus Requirements 44

4.3 Summary of Results 54

4.4 Conclusions 55

5\. EVALUATION OF AUGMENTED GPS ARCHITECTURES 57

5.1 Eliminating Systems 57

5.2 Composite Architectures 58

5.3 Architecture Evaluation 60

5.4 Summary of Results 65

6\. RECOMMENDATIONS 67

6.1 Recommended Architecture 67

6.2 Architecture Independent Recommendations 67

7\. REFERENCES 69

APPENDIX A: ACRONYMS AND ABBREVIATIONS A-1

APPENDIX B: DEFINITIONS B-1

APPENDIX C: GPS USER\'S WORKSHOP AND USER SURVEY C-1

APPENDIX D: GPS BACKGROUND D-1

APPENDIX E: JAMMING AND SPOOFING OF AUGMENTED GPS E-1

APPENDIX F: EVALUATION OF DGPS DATA FORMATS F-1

APPENDIX G: AUGMENTATION DESCRIPTIONS G-1

APPENDIX H: COVERAGE AND AVAILABILITY OF LF/MF RADIOBEACONS H-1

APPENDIX I: CAPABILITIES TABLE VALUES I-1

APPENDIX J: DEVELOPMENT OF THE WEIGHTEDANALYTICAL DECISION MATRIX J-1

APPENDIX K: ARCHITECTURE EVALUATION K-1

**LIST OF FIGURES**

Page

Figure 3-1. Block diagram of USCG LF/MF radiobeacon system 23

Figure 3-2. Predicted coverage area for the USCG LF/MF radiobeacon
system 24

Figure 3-3. Predicted coverage area for 41 additional LF/MF radiobeacons
26

Figure 3-4. Predicted composite coverage for USCG(E) system with 102
radiobeacons 26

Figure 3-5. Block diagram of FM subcarrier system 28

Figure 3-6. Predicted coverage area for an FM subcarrier system 29

Figure 3-7. Block diagram of FAA Wide Area Augmentation System 31

Figure 3-8. Block diagram of a proposed FAA local area DGPS system 33

Figure 3-9. Coverage provided by U.S.-operated or -provided Loran-C
stations 41

Figure 5-1. Architecture comparison, performance vs. cost 63

Figure 5-2. Architecture comparison, performance vs. security 64

Figure 5-3. Architecture comparison, security vs. cost 64

**LIST OF TABLES**

Page

Table 2-1. IVHS Navigation and Positioning Requirements 9

Table 2-2. Railroad Navigation and Positioning Requirements 10

Table 2-3. Marine Navigation and Positioning Requirements 11

Table 2-4. Air Navigation and Positioning Requirements 12

Table 2-5. Non-Transportation Positioning/Timing Requirements 14

Table 2-6. Summary of Navigation and Positioning Requirements 16

Table 4-1. Augmented GPS System Capabilities 45

Table 4-2. Augmented GPS System Evaluation, Aviation, Oceanic En Route
46

Table 4-3. Augmented GPS System Evaluation, Aviation, Domestic En Route
46

Table 4-4. Augmented GPS System Evaluation, Aviation, Terminal 47

Table 4-5. Augmented GPS System Evaluation, Aviation, Non Precision
Approach 47

Table 4-6. Augmented GPS System Evaluation, Aviation, Category I
Approach 48

Table 4-7. Augmented GPS System Evaluation, Marine, Harbor/Harbor
Approach 48

Table 4-8. Augmented GPS System Evaluation, Marine, Coastal 49

Table 4-9. Augmented GPS System Evaluation, Marine, Ocean 49

Table 4-10. Augmented GPS System Evaluation, Land, Highway 50

Table 4-11. Augmented GPS System Evaluation, Land, Highway (Collision
Avoidance) 50

Table 4-12. Augmented GPS System Evaluation, Land, Railroad 51

Table 4-13. Augmented GPS System Evaluation, Land, Railroad (Control) 51

Table 4-14. Augmented GPS System Evaluation, Survey, Land 52

Table 4-15. Augmented GPS System Evaluation, Survey, Hydro 52

Table 4-16. Augmented GPS System Evaluation, Survey, Deformation
Analysis 53

Table 4-17. Augmented GPS System Evaluation, Survey, Mapping 53

Table 4-18. Augmented GPS System Evaluation, Aviation, Summary 54

Table 4-19. Augmented GPS System Evaluation, Marine, Summary 54

Table 4-20. Augmented GPS System Evaluation, Land, Summary 54

Table 4-21. Augmented GPS System Evaluation, Survey, Summary 55

Table 4-22. Augmented GPS System Evaluation, Mode, Summary 55

Table 5-1. Weighted Analytical Decision Matrix --- Performance 62

Table 5-2. Weighted Analytical Decision Matrix --- Cost 62

Table 5-3. Weighted Analytical Decision Matrix --- Security 62

**EXECUTIVE SUMMARY**

Early in 1993, the Secretaries of Defense and Transportation recognized
the expanding utility of the Navstar Global Positioning System (GPS) for
both military and civilian applications. The Secretaries chartered a
Joint Task Force to assess the growing utility of the system and make
recommendations for expanding civil use. In December 1993, the Joint
Task Force concluded its deliberations and reported its findings and
recommendations to the Secretaries. Included in the Task Force report
was a recommendation for a study of all differential GPS (DGPS) services
under development or deployment to determine the optimum integrated
approach to providing augmented GPS services.

In response to the Task Force recommendation, the Department of
Transportation (DOT), with the support and assistance of the Department
of Defense (DOD) and the Department of Commerce (DOC), undertook a study
to evaluate the capabilities of various means of augmenting GPS and to
determine the optimum integrated system for meeting the requirements of
Federal land, marine, aviation, and space users. This report presents
the findings of that study.

**Study Participants**

Using an existing Federal Highway Administration (FHWA) contractual
relationship, the DOT engaged the services of the Institute for
Telecommunication Sciences (ITS) of the National Telecommunications and
Information Administration (NTIA) to conduct the study. ITS provided a
broad background in communication systems, navigation systems, systems
planning and analysis, standards development, and spectrum management.
To augment its expertise, ITS obtained the services of additional
technical specialists. The U.S. Army Topographic Engineering Center
(TEC) provided technical expertise and experience with the development
of GPS and positioning and navigation systems. DOT's Volpe National
Transportation Systems Center added extensive overall knowledge of
transportation systems. Overlook Systems Technologies, Inc. furnished
expertise on aviation systems and Federal Aviation Administration (FAA)
requirements. Representatives from these organizations formed a study
team, led by ITS, that carried out the study. Study team meetings
provided opportunity for input from other agencies. Study oversight was
provided by a Study Review Board representing the Office of the
Secretary of Transportation, FHWA, DOT\'s Research and Special Programs
Administration, FAA, U.S. Coast Guard (USCG), DOD, and the National
Oceanic and Atmospheric Administration (NOAA). The Study Review Board
appointed a Working Group to support the efforts of the study team.

**Approach**

The study began with a detailed examination of the current and future
navigation and positioning requirements of Federal land, marine,
aviation, and space users. The primary sources of requirements
information consisted of the following:

> • Responses from Federal agencies to a Secretary of Transportation
> request for statements of intended uses for GPS.
>
> • A workshop for Federal GPS users, conducted by ITS and TEC.
>
> • Responses from Federal agencies to a survey generated and
> distributed by the study team.

The study team found that the requirements of Federal agencies vary
widely, but they can be summarized as follows:

> **Accuracy**.  The range of accuracy required is from 1 mm to 1000 m.
> The highest accuracy is required for surveying. The FAA requires only
> 1000 m accuracy for en route navigation, but requires 4.1 m (13.5 ft)
> horizontal and 0.6 m (2 ft) vertical accuracy for Category III
> precision approach and landing.
>
> **Time to Alarm**.  Requirements for the elapsed time between a system
> failure and notification to the user range from 1 second for certain
> land transportation applications to hours for post-processing survey
> applications.
>
> **Availability**.  Most users have a need for greater than 99.7%
> availability. Some railroad applications require availability of 100%.
>
> **Coverage Area**.  Federal users require nationwide coverage both at
> ground level and in the volume above ground and over that part of the
> oceans which constitutes the National Airspace System. Worldwide
> coverage for a seamless transition to foreign systems is highly
> desirable.

Concurrent with the requirements analysis, the study team researched
existing and planned augmented GPS systems. Systems examined included
Federal, private, and foreign systems. Eighteen systems were identified
as potential alternatives to meet Federal requirements for navigation
and positioning. The study team selected 11 systems from among these
alternatives for detailed evaluation. This selection was based on
technical feasibility, capability of meeting user requirements, and
current implementation or likely implementation in the near future.

The study team subjected the 11 candidate systems to a more detailed
analysis using a specially constructed, two-stage decision matrix. In
the first stage of the decision matrix, the study team listed the
detailed performance requirements of Federal users and evaluated the
ability of each of the candidate systems to meet these requirements.
From this stage of the decision analysis, the study team determined that
no single existing or planned augmented GPS system is capable of meeting
all requirements of all users. With this determination made, the study
team proposed six potential composite architectures intended to satisfy
as many user requirements as possible. The six composite architectures
are summarized briefly in the following paragraphs:

> **Architecture 1**.  This architecture, the baseline system, consisted
> of the GPS augmentation systems currently planned by USCG and FAA. It
> included the 61-site local area differential GPS (LADGPS) system
> currently being implemented by USCG for marine use, FAA's Wide Area
> Augmentation System (WAAS) as currently planned to satisfy aviation
> requirements for en route through Category I precision approach, and
> FAA\'s LADGPS systems to satisfy Category II/III precision approach
> requirements. All of the reference stations included in this
> architecture would be compliant with the Continuously Operating
> Reference Station (CORS) standard. Such stations would have the
> capability of storing a standardized set of data to support the widest
> possible number of post-processing applications. Although Architecture
> 1 did not satisfy many land transportation and survey requirements, it
> was included to provide a benchmark against which the remaining five,
> more viable alternatives could be compared.
>
> **Architecture 2**.  This architecture consisted of an expanded
> version of USCG\'s LADGPS system to provide nationwide coverage for
> marine [and]{.underline} land users. It also included FAA's WAAS as
> currently planned to satisfy aviation requirements for en route
> through Category I precision approach, and FAA\'s LADGPS systems to
> satisfy Category II/III precision approach requirements. All of the
> reference stations included in this architecture would comply with the
> CORS standard.
>
> **Architecture 3**.  This architecture consisted of an expanded
> version of USCG\'s LADGPS system to provide nationwide coverage for
> marine and land users and a variant of FAA's WAAS to satisfy aviation
> requirements for en route through nonprecision approach only. Category
> I, II, and III precision approach requirements would be satisfied by
> FAA\'s LADGPS systems. All of the reference stations included in this
> architecture would comply with the CORS standard.
>
> **Architecture 4**.  This architecture included an expanded version of
> USCG\'s LADGPS system to provide nationwide coverage for marine and
> land users. It also included a modified version of FAA's WAAS, which
> provided corrections at other than the GPS L1 frequency, to satisfy
> aviation requirements for en route through Category I precision
> approach. Category II/III precision approach requirements would be
> satisfied by FAA\'s LADGPS systems. All of the reference stations
> included in this architecture would comply with the CORS standard.

**Architecture 5**.  This architecture included an expanded version of
USCG\'s LADGPS system to provide nationwide coverage for marine and land
users. It also included a modified version of the FAA's WAAS which would
encrypt all of the corrections for increased security. The modified WAAS
would satisfy aviation requirements for en route through Category I
precision approach. Category II/III precision approach requirements
would be satisfied by FAA\'s LADGPS systems. All of the reference
stations included in this architecture would comply with the CORS
standard.

**Architecture 6**.  This architecture included an expanded version of
USCG\'s LADGPS system to provide nationwide coverage for marine and land
users and to satisfy aviation accuracy requirements for Category I
precision approach. It also included a variant of the FAA\'s WAAS to
satisfy aviation requirements for en route through nonprecision
approach. Category II/III precision approach requirements would be
satisfied by FAA\'s LADGPS systems. All of the reference stations
included in this architecture would comply with the CORS standard.

Architecture 6 was evaluated extensively as it appeared capable of
meeting stated requirements at a lower cost than the other five
architectures. In the course of the evaluation, it was found that
possible interference of signal reception could occur to aircraft which
were flying through conditions conducive to the creation of
precipitation static (P-Static). While an extensive study had not been
performed of this phenomenon, it raised significant concerns about
signal availability. Consequently, Architecture 6 was not considered in
the second stage of the decision matrix.

The remaining five composite architectures were evaluated using the
second stage of the decision matrix, which constituted a modified
version of a classic multi-attribute utility analysis. The second stage
of the matrix consisted of a model with three major parameters:
Performance, Cost, and Security. These major parameters were broken down
into the individual factors shown below:

**Performance** ---

> • Real Time Accuracy.
>
> • Integrity (Time to Alarm).
>
> • Availability.
>
> • Time Frame of Availability (Initial Operating Capability).
>
> • Coverage.
>
> • International Compatibility.

**Cost** ---

> • Infrastructure Cost.
>
> • User Cost.

**Security** ---

> • Access Control.
>
> • Level of Influence.
>
> • Interdiction.
>
> • Post-Decision Response Time.
>
> • Jammability.
>
> • Vulnerability of Denial.

Importance weights were assigned to each of the factors under each
parameter. Each factor was then assigned a relative score ranging from
100 for the best architecture to 0 for the worst architecture. The
second stage of the decision matrix provided a numerical score for each
composite architecture for each parameter. A multi-attribute decision
analysis would have assigned relative importance weights to the
individual parameters themselves and, using these weights, derived a
single aggregate score for each architecture. However, in this study, no
attempt was made to assign relative importance weights to the parameters
since to do so would have involved making value judgments that were
beyond the scope of the study. Rather, the study team and Working Group
concluded that the primary utility of the decision matrix was its
ability to facilitate brainstorming, assist in developing a greater
awareness of what the key decision factors might be, and highlight areas
of uncertainty. Further, the decision matrix aided in composing and
performing a series of sensitivity analyses.

**Conclusions**

There are two candidates that could be selected as the National
augmentation architecture. The selection of one of these two viable
alternatives is dependent on overall U.S. Government policy regarding
augmentation systems.

• If security concerns are not the overriding consideration and do not
predominate over other benefits available from an augmented GPS,
composite Architecture 2 is the recommended National augmentation
system.

• If, however, security concerns are of such significance as to
predominate over economic and other benefits available from an augmented
GPS, then Architecture 3 is the recommended National augmentation
system.

Either of these architectures will meet aviation user requirements for
all phases of flight, marine user requirements for all modes of
operation, and most land user requirements including IVHS, railroad, and
survey. However, neither architecture will satisfy highway collision
avoidance because of the high degree of accuracy (1 meter) required
nationwide. Neither architecture will provide the 100% availability
required for railroad collision avoidance. These applications may
require the development or use of other technologies either in
conjunction with or independent of GPS.

**Recommendations**

Based on its research and evaluation, the study team recommends the
following:

> • FAA should continue to implement its WAAS and LADGPS systems as
> currently planned.
>
> • DOT, in coordination and cooperation with DOC, should plan, install,
> operate, and maintain an expanded low frequency/medium frequency
> beacon system modeled after USCG\'s LADGPS system to provide
> nationwide coverage for land and marine users. Prior to implementing
> this system, a study should be performed to determine the number and
> optimum location of beacons necessary for nationwide coverage.
>
> • All Federally-provided reference stations should comply with the
> CORS standard.
>
> • DOT should continue to evaluate system risks and appropriate
> measures needed to ensure safe and reliable augmentation services.
> Further, DOT, with the assistance of DOD, should test and evaluate
> measures to mitigate the susceptibility of Federally-provided
> augmentation systems to all forms of interference, including jamming
> and spoofing.
>
> • DOT, in conjunction with other Federal agencies, should coordinate
> the implementation, operation, and maintenance of all
> Federally-operated augmented GPS systems to ensure optimal use of
> resources by maximizing commonality of system components.
>
> • Different formats for augmentation data have been developed to meet
> the requirements of particular user communities and to make optimum
> use of data links planned for augmenting GPS. For the architectures
> considered, there is no compelling technical or economic reason for
> developing a single, standardized data format for use by all
> Federally-operated augmentation systems. Consequently, no effort
> should be expended on the conversion of existing broadcast formats to
> a common data format in the near term. Use of the Receiver Independent
> Exchange (RINEX) format is recommended for post-processing
> applications. In addition, an international standards working group
> should be identified to address any future data format issues.
>
> • A central repository for GPS augmentation information should be
> maintained. This information should be made available to the public
> via the existing USCG Navigation Information Service.
>
> • A further study should be undertaken to investigate spectrum
> allocation and bandwidth requirements for any future,
> Federally-provided, differential GPS system.

**A TECHNICAL REPORT TO THE**

**SECRETARY OF TRANSPORTATION ON A**

**NATIONAL APPROACH TO AUGMENTED GPS SERVICES**

Robert O. DeBolt, Roger A. Dalke, Ronald L. Ketchum,

George A. Hufford, Michael Terada, Wayne R. Rust[^1]

Sally L. Frodge, Robert G. Mann, Frederick M. Gloeckler,

Thomas M. Cox, Daniel C. Oimoen, James C. Eichholz[^2]

Elisabeth J. Carpenter[^3]

John H. Martel, Jeffrey A. Johnson[^4]

**ABSTRACT**

This report documents the development of recommendations for a national
approach to augmented Global Positioning System (GPS) services. The
Institute for Telecommunication Sciences led a study team that included
the U.S. Army Topographic Engineering Center, the Volpe National
Transportation Systems Center, and Overlook Systems Technologies, Inc.
The study team identified Federal navigation, positioning, and timing
requirements for land, marine, air, and space modes of operation. The
study team then evaluated numerous operating and proposed systems that
augment the GPS Standard Positioning Service. The most promising systems
were combined in six different architectures intended to meet the widest
possible range of user requirements. One of these architectures was
eliminated from consideration due to technical concerns. The study team
evaluated each of the remaining architectures against a set of
performance, cost, and security factors. Based on the architecture
evaluations, the study team developed a set of recommendations for a
coordinated, national approach to augmented GPS services that meets
Federal requirements while avoiding unnecessary duplication of
facilities.

Key words: Global Positioning System (GPS); differential GPS (DGPS); GPS
Precise Positioning Service (PPS); GPS Standard Positioning Service
(SPS)

**1**

**INTRODUCTION**

In December of 1993, the U.S. Departments of Defense and Transportation
(DOD and DOT) published a Joint Task Force report entitled *The Global
Positioning System: Management and Operation of a Dual Use System*
\[1\]. The report notes that the Federal Government is committed to
selecting radionavigation systems which meet diverse user requirements
for accuracy, reliability, coverage, integrity, and cost while
eliminating unnecessary duplication of facilities and services. The
report states that GPS is the system capable of meeting the widest range
of military and civilian navigation and positioning requirements. It
further notes that with the implementation of augmented GPS, several
radionavigation systems currently provided and used by the U.S. Coast
Guard (USCG), the Federal Aviation Administration (FAA), and the DOD
could be phased out.

To satisfy many user requirements, GPS must be augmented with correction
information that is applied by the user to standard civilian GPS
signals. Currently, several government operating administrations, such
as USCG and FAA, and private industry, including broadcasting companies
and satellite service providers, are developing augmented GPS systems
for various uses. The Joint Task Force report concludes:

> \"Because several augmentation alternatives are under development to
> support multiple applications, a study of all such alternatives is
> required to develop an optimum integrated system to provide augmented
> GPS services.\"

This report documents the results of the recommended study of
alternative augmented GPS systems.

**1.1  Objective**

The objective of the study was to evaluate the capabilities of augmented
GPS systems and determine the optimum integrated system for meeting the
navigation and positioning require­ments of Federal land, marine,
aviation, and space users. Augmented GPS systems may also meet most, if
not all, of the positioning requirements of public and private users
outside the DOT.

**1.2  Scope**

The recommendations of this report provide an independent expert opinion
to assist DOT in determining which GPS augmentation(s) should be
implemented. Factors bearing on the recommendations include:

> • Ability of GPS augmentations to meet Federal user navigation and
> positioning requirements.
>
> • Federal development and deployment cost.
>
> • User cost.
>
> • Ability of GPS augmentations to meet user safety and national
> security requirements.

**1.3  Study Participants**

Using an existing Federal Highway Administration (FHWA) contractual
relationship, the DOT engaged the services of the Institute for
Telecommunication Sciences (ITS) of the National Telecommunications and
Information Administration (NTIA) to conduct the study. ITS provided a
broad background in communication systems, navigation systems, systems
planning and analysis, standards development, and spectrum management.
To augment its expertise, ITS obtained the services of additional
technical specialists. The U.S. Army Topographic Engineering Center
(TEC) provided technical expertise and experience with the development
of GPS and positioning and navigation systems. DOT's Volpe National
Transportation Systems Center added extensive overall knowledge of
transportation systems. Overlook Systems Technologies, Inc. furnished
expertise on aviation systems and FAA requirements. Representatives from
these organizations formed a study team, led by ITS, that carried out
the study. Study team meetings provided opportunity for input from other
agencies. Study oversight was provided by a Study Review Board
representing the Office of the Secretary of Transportation, FHWA, DOT\'s
Research and Special Programs Administration, FAA, USCG, DOD, and the
National Oceanic and Atmospheric Administration. The Study Review Board
appointed a Working Group to support the efforts of the study team.

**1.4  Study Tasks**

The study was broken down into the following tasks:

> 1\) Identification of the requirements of Federal land, marine,
> aviation, and space users for navigation and positioning, including
> geophysical positioning, geodetic surveying, resource mapping, timing,
> and meteoro­logical and ionospheric monitoring.

2\) Evaluation of Federal and private GPS augmentations and examination
of foreign augmentations for meeting these requirements.

3\) Review of the susceptibility of GPS augmentations to malicious or
hostile use.

4\) Evaluation of the data formats provided by the Radio Technical
Commission for Maritime Services (RTCM) and RTCA, Inc. for possible
standardization.

5\) Recommendation of which GPS augmentation(s) should be employed to
satisfy Federal requirements without compromising national security.

The results of these tasks are described in the following sections of
this report. Definitions of acronyms, abbreviations, and terms used
throughout this report are contained in Appendices A and B.

**1.5  Study Approach**

The study began with a detailed examination of the current and future
navigation and positioning requirements of Federal land, marine,
aviation, and space users. The primary sources of requirements
information consisted of the following:

• Responses from Federal agencies to a Secretary of Transportation
request for statements of intended uses for GPS.

• A workshop for Federal GPS users, conducted by TEC and ITS.

• Responses from Federal agencies to a survey generated and distributed
by the study team.

Concurrent with the requirements analysis, the study team researched
existing and planned augmented GPS systems. Systems investigated
included Federal, private, and foreign systems. Eighteen systems were
identified as potential alternatives to meet Federal requirements for
navigation and positioning. The study team selected 11 of the 18 systems
for detailed evaluation. This selection was based on technical
feasibility, capability of meeting user requirements, and current
implementation or likely implementation in the near future.

The study team subjected the 11 candidate systems to a more detailed
analysis using a specially constructed, two-stage decision matrix. In
the first stage of the decision matrix, the study team listed the
detailed performance requirements of Federal users and evaluated the
ability of each of the candidate systems to meet these requirements.
From this stage of the decision analysis, the study team determined that
no single existing or planned augmented GPS system was capable of
meeting all user requirements.

With this determination made, the study team proposed potential
composite architectures, comprised of combinations of these 11 systems.
These architectures were generated to satisfy as many user requirements
as possible.

The study team evaluated these architectures using the second stage of
the decision matrix, which constituted a modified version of a classic,
multi-attribute, utility analysis. The second stage of the matrix
consisted of a model with three major parameters: Performance, Cost, and
Security. Each parameter was further subdivided into a number of
factors, and weights were assigned to each of the factors. Each factor
was then assigned a relative score ranging from 100 for the best
architecture to 0 for the worst architecture. Scores for the potential
architectures were compared to help the study team reach its
conclusions.

**2**

**FEDERAL USER REQUIREMENTS**

**FOR NAVIGATION AND POSITIONING**

This section identifies navigation and positioning requirements for
Federal agencies serving transportation and non-transportation users.
Information to support this effort was collected from:

> • *The Global Positioning System: Management and Operation of a Dual
> Use System* \[1\].
>
> • *1992 Federal Radionavigation Plan* \[2\].
>
> • *DRAFT 1994 Federal Radionavigation Plan* \[3\].
>
> • Federal GPS User\'s Workshop and User Survey, conducted by TEC and
> ITS in March 1994. Appendix C contains a list of the agencies
> contacted and a copy of the user survey.
>
> • *DRAFT National Program Plan for Intelligent Vehicle-Highway
> Systems* \[4\].
>
> • A thorough review of the literature in the field, including numerous
> articles, reports, and studies.
>
> • Interviews with and field visits to Federal GPS users and GPS
> receiver manufacturers.
>
> • Attendance at the XXth Congress of the International Federation of
> Surveyors (FIG), Melbourne, Australia, March 27--April 1, 1994; the
> Institute of Electrical and Electronics Engineers (IEEE) Position
> Location and Navigation Symposium (PLANS), Las Vegas, Nevada, April
> 11--15, 1994; Differential Satellite Navigation Systems 1994 (DSNS
> \'94), London, England, April 17--21, 1994; and the Institute of
> Navigation (ION) 50th Annual Meeting, Colorado Springs, Colorado, June
> 6--8, 1994.

Although Federal users described many different requirements, the study
team found that nearly all users specified requirements for accuracy,
integrity (time to alarm), availability, and coverage. Requirements in
these common areas provide a key means for discriminating between the
various augmentation systems that are described and evaluated in
Sections 3 and 4. Requirements are identified in the following sections
for land, marine, air, and space transportation users and for
non-transportation users.

**2.1  Land Transportation Requirements**

Navigation and positioning requirements for land transportation are
divided into two categories:

> 1\) Support of Intelligent Vehicle Highway Systems (IVHS).
>
> 2\) Support of railroad traffic management.

**IVHS.  **The primary goals of IVHS are improved safety and more
efficient use of the existing infrastructure. Thousands of lives and
billions of dollars are expected to be saved each year through the use
of IVHS. In 1991, the U.S. government committed itself to IVHS by
allocating \$659 million over six years under the Intermodal Surface
Transportation Efficiency Act \[5\]. There are six major IVHS program
areas:

> • Traffic Management --- includes systems which collect and process
> real-time traffic information to control adaptive signals, ramps, and
> signs.
>
> • Traveler Information --- includes systems which provide information
> on location of vehicles and services, traffic conditions, and
> preferred routes.
>
> • Vehicle Control --- includes systems which monitor vehicle
> position/velocity and road conditions to avoid collisions and automate
> certain aspects of vehicle operation.
>
> • Public Transportation --- includes systems which optimize the
> movement of buses and trains through traffic and deliver location
> information to transit users and fleet managers.
>
> • Rural Transportation --- includes systems which provide navigation
> aids, deliver information on dangerous weather or road conditions, and
> transmit a distress alert in case of an accident or breakdown.
>
> • Commercial Vehicle Operations --- includes systems which provide
> automated vehicle identification/automated vehicle location (AVI/AVL)
> to improve dispatching, fleet management, and monitoring of hazardous
> materials transport.

Navigation and positioning requirements for IVHS applications within
these program areas are still under study and not yet fully defined.
Known requirements are summarized in Table 2-1.

Table 2-1.  IVHS Navigation and Positioning Requirements

+--------------+------------+-------------+------------+------------+
| IVHS         | Accuracy   | Time to     | Av         | Coverage   |
|              |            |             | ailability |            |
| Application  | (2 drms)   | Alarm       |            | Area       |
+--------------+------------+-------------+------------+------------+
| Navigation   | 5-20       | 1-15        | 99.7%      | nationwide |
| and          | meters     | seconds     |            |            |
|              |            |             |            |            |
| Route        |            |             |            |            |
| Guidance     |            |             |            |            |
+--------------+------------+-------------+------------+------------+
| May          | 5-30       | 1-15        | 99.7%      | nationwide |
| day/Incident | meters     | seconds     |            |            |
| Alert        |            |             |            |            |
+--------------+------------+-------------+------------+------------+
| Fleet        | 25-1500    | 1-15        | 99.7%      | nationwide |
| Management   | meters     | seconds     |            |            |
|              |            |             |            |            |
| (AVI/AVL)    |            |             |            |            |
+--------------+------------+-------------+------------+------------+
| Automated    | 5-30       | 1-15        | 99.7%      | nationwide |
| Bus/Rail     | meters     | seconds     |            |            |
| Stop         |            |             |            |            |
| Announcement |            |             |            |            |
+--------------+------------+-------------+------------+------------+
| Vehicle      | 30-50      | 1-15        | 99.7%      | nationwide |
| Command and  | meters     | seconds     |            |            |
| Control      |            |             |            |            |
+--------------+------------+-------------+------------+------------+
| Collision    | 1 meter    | 1-15        | 99.7%      | critical   |
| Avoidance:   |            | seconds     |            |            |
|              |            |             |            | locations  |
| Control      |            |             |            |            |
+--------------+------------+-------------+------------+------------+
| Collision    | 5 meters   | 1-15        | 99.7%      | critical   |
| Avoidance:   |            | seconds     |            |            |
|              |            |             |            | locations  |
| Hazardous    |            |             |            |            |
| Situation    |            |             |            |            |
+--------------+------------+-------------+------------+------------+
| Accident     | 30 meters  | 1-15        | 99.7%      | nationwide |
| Data         |            | seconds     |            |            |
| Collection   |            |             |            |            |
+--------------+------------+-------------+------------+------------+
| In           | 10 meters  | 1-15        | 99.7%      | nationwide |
| frastructure |            | seconds     |            |            |
| Management   |            |             |            |            |
+--------------+------------+-------------+------------+------------+

**Railroads.  **Most railroads manage traffic through the use of
timetables, block signaling, or centralized traffic control. Block
signaling involves the use of signals which are set when a section of
track is occupied by a train. Centralized traffic control allows a
dispatcher to control train movement from a distant location by the
remote monitoring of track circuits and automatic route interlocking.

Several critical elements of advanced train control systems, including
positive train control and positive train separation, have been tested
or are under development by the railroad industry. These advanced
systems use the knowledge of train location and speed, the input from a
variety of railway sensors, and a data communication network to manage
railroad traffic more effectively. These systems increase train safety
and improve the operating efficiency of the railroad system.

The developing navigation and positioning requirements for railroad
applications are summarized in Table 2-2. These requirements have been
gathered from industry sources and have not yet been validated. \"Train
Position Tracking\" refers to determining the position of each end of a
train with respect to a block of track. Such a relatively gross tracking
capability provides a primarily economic benefit to a railroad in
maximizing the utilization of a section of track. \"Train Control\"
refers to the dynamic supervision of multiple trains on a known track
structure which may include parallel tracks and numerous switches. The
stringent accuracy requirement for train control stems from the need to
distinguish between parallel tracks that may be spaced as close as 3.8 m
(12.5 ft) center-to-center. Collision avoidance, or \"positive train
separation,\" is an aspect of train control.

Table 2-2.  Railroad Navigation and Positioning Requirements

+--------------+----------------+--------------+----------+----------+
| Railroad     | Accuracy       | Time to      | Avai     | Coverage |
|              |                |              | lability |          |
| Application  | (2 drms)       | Alarm        |          | Area     |
+--------------+----------------+--------------+----------+----------+
| Train        | 10-30 meters   | 5 seconds    | 99.7%\*  | na       |
| Position     |                |              |          | tionwide |
| Tracking     |                |              |          |          |
+--------------+----------------+--------------+----------+----------+
| Speed        | ±1 km/hour for | 5 seconds    | 99.7%    | na       |
| D            |                |              |          | tionwide |
| etermination | speeds \< 20   |              |          |          |
|              | km/hour        |              |          |          |
|              |                |              |          |          |
|              | ±5% for        |              |          |          |
|              |                |              |          |          |
|              | speeds ≥ 20    |              |          |          |
|              | km/hour        |              |          |          |
+--------------+----------------+--------------+----------+----------+
| Train        | 1 meter        | less than    | 100%     | na       |
| Control      |                |              |          | tionwide |
|              |                | 5 seconds†   |          |          |
+--------------+----------------+--------------+----------+----------+
| Automated    | 1 meter        | less than    | 100%     | na       |
| Road Vehicle |                |              |          | tionwide |
| Warning at   |                | 5 seconds    |          |          |
|              |                |              |          |          |
| R            |                |              |          |          |
| ailroad/Road |                |              |          |          |
| Grade        |                |              |          |          |
| Crossings    |                |              |          |          |
+--------------+----------------+--------------+----------+----------+

\*Some sources believe that this requirement can be relaxed.

†This requirement may need to be more stringent for high speed passenger
rail applications.

**2.2  Marine Transportation Requirements**

The 1992 FRP describes four major phases of marine transportation:
inland waterway, harbor/harbor approach, coastal, and ocean. Navigation
and positioning requirements for inland waterways have not yet been
defined by USCG or the marine community, but requirements for the other
three phases are summarized in Table 2-3.

Table 2-3.  Marine Navigation and Positioning Requirements

+-------------+---------------+------------+------------+-------------+
| Marine      | Accuracy      | Time to    | Av         | Coverage    |
|             |               |            | ailability |             |
| Application | (2 drms)      | Alarm      |            | Area        |
+-------------+---------------+------------+------------+-------------+
| Ha          | 8-20 meters   | 6-10       | 99.7%      | U.S.        |
| rbor/Harbor |               | seconds    |            | harbors and |
| Approach;   |               |            |            | approaches  |
|             |               |            |            |             |
| Large Ships |               |            |            |             |
| and Tows    |               |            |            |             |
+-------------+---------------+------------+------------+-------------+
| Ha          | 8-20 meters   | 6-10       | 99.9%      | U.S.        |
| rbor/Harbor |               | seconds    |            | harbors and |
| Approach;   |               |            |            | approaches  |
|             |               |            |            |             |
| Smaller     |               |            |            |             |
| Ships       |               |            |            |             |
+-------------+---------------+------------+------------+-------------+
| Ha          | 1-3 meters    | 5 seconds  | 99.0%      | U.S.        |
| rbor/Harbor |               |            |            | harbors and |
| Approach;   |               |            |            | approaches  |
|             |               |            |            |             |
| Resource    |               |            |            |             |
| Exploration |               |            |            |             |
+-------------+---------------+------------+------------+-------------+
| Coastal;    | 460 meters    | not        | 99.7%      | U.S.        |
| All Ships   |               | specified  |            | coastal     |
|             | (0.25         |            |            | waters      |
|             | nautical      |            |            |             |
|             | miles)        |            |            |             |
+-------------+---------------+------------+------------+-------------+
| Coastal;    | 460-3700      | not        | 99.0%      | U.S.        |
| Recreation  | meters        | specified  |            | coastal     |
| Boats and   |               |            |            | waters      |
| Other       | (0.25-2       |            |            |             |
| Smaller     | nautical      |            |            |             |
| Vessels     | miles)        |            |            |             |
+-------------+---------------+------------+------------+-------------+
| Ocean;      | 3700-7400     | not        | 99.0%      | worldwide   |
| Safety of   | meters        | specified  |            |             |
| Navigation  |               |            |            |             |
|             | (2-4 nautical |            |            |             |
|             | miles)        |            |            |             |
+-------------+---------------+------------+------------+-------------+
| Ocean; All  | 1800-3700     | not        | 99.0%      | worldwide   |
| Craft       | meters        | specified  |            |             |
|             |               |            |            |             |
|             | (1-2 nautical |            |            |             |
|             | miles)        |            |            |             |
+-------------+---------------+------------+------------+-------------+

**2.3  Air Transportation Requirements**

The 1992 FRP describes two basic phases of air transportation: en
route/terminal and approach/landing. The en route/terminal phase
includes all portions of flight to within 18,500 meters (10 nautical
miles) of the runway. It includes oceanic, domestic, and terminal
subphases. The approach/landing phase includes that portion of flight
conducted immediately prior to touchdown. The navigation and positioning
requirements for air transportation are summarized in Table 2-4. The use
of aircraft for applications other than transportation, such as aerial
surveying and mapping, is discussed in Section 2.5. Programs are
underway to study the use of GPS for Automatic Dependent Surveillance
and ground positioning and tracking on airport surfaces, but no
requirements had been validated at the time of this study.

Table 2-4.  Air Navigation and Positioning Requirements

+---------------+--------------+------------+----------+-------------+
| Air Transport | Accuracy     | Time to    | Avai     | Coverage    |
|               |              |            | lability |             |
| Category      | (2 drms)     | Alarm      |          | Altitude    |
+---------------+--------------+------------+----------+-------------+
| En Route      | 23 km        | 30 seconds | 99.977%  | 8400-12,200 |
| Oceanic       |              |            |          | m           |
|               | (12.6        |            |          |             |
|               | nautical     |            |          | (27         |
|               | miles)       |            |          | ,500-40,000 |
|               |              |            |          | ft)         |
+---------------+--------------+------------+----------+-------------+
| En Route      | 1000 m       | 10 seconds | 99.977%  | 150-18,300  |
| Domestic      |              |            |          | m           |
|               |              |            |          |             |
|               |              |            |          | (500-60,000 |
|               |              |            |          | ft)         |
+---------------+--------------+------------+----------+-------------+
| Terminal      | 500 m        | 10 seconds | 99.977%  | 150-5500 m  |
|               |              |            |          |             |
|               |              |            |          | (500-18,000 |
|               |              |            |          | ft)         |
+---------------+--------------+------------+----------+-------------+
| Appr          | 100 m        | 10 seconds | 99.977%  | 75-900 m    |
| oach/Landing: |              |            |          |             |
|               |              |            |          | (250-3000   |
| Non-Precision |              |            |          | ft)         |
+---------------+--------------+------------+----------+-------------+
| Appr          | horiz:  17.1 | 6 seconds  | 99.999%  | 30-900 m    |
| oach/Landing: | m            |            |          |             |
|               |              |            |          | (100-3000   |
| Precision     | vert:  4.1 m |            |          | ft)         |
| Category I    |              |            |          |             |
+---------------+--------------+------------+----------+-------------+
| Appr          | horiz:  5.2  | 2 seconds  | 99.999%  | 15-900 m    |
| oach/Landing: | m            |            |          |             |
|               |              |            |          | (50-3000    |
| Precision     | vert:  1.7 m |            |          | ft)         |
| Category II   |              |            |          |             |
+---------------+--------------+------------+----------+-------------+
| Appr          | horiz:  4.1  | 2 seconds  | 99.999%  | 0-900 m     |
| oach/Landing: | m            |            |          |             |
|               |              |            |          | (0-3000 ft) |
| Precision     | vert:  0.6 m |            |          |             |
| Category III  |              |            |          |             |
+---------------+--------------+------------+----------+-------------+

**2.4  Space Transportation Requirements**

The 1992 FRP divides space missions into three phases: ground launch,
on-orbit, and reentry and landing. Space transportation applications
related to these phases include:

> • Control and navigation of the U.S. Space Shuttle, other launch
> vehicles, automated spacecraft, and interplanetary or lunar spacecraft
> returning to Earth orbit.
>
> • Determination of spacecraft position, altitude, and velocity.
>
> • Guidance of spacecraft in the vicinity of other spacecraft or
> orbiting platforms (e.g. rendezvous).

Navigation and positioning requirements for space transportation remain
under study and are expected to be updated in the 1994 FRP.

**2.5  Non-Transportation Requirements**

Federal users have several types of non-transportation applications that
require precise positioning and timing information. These include:

> • Remote Sensing --- Space-based remote sensing techniques are
> commonly used to gather weather data and monitor environmental
> conditions.
>
> • Search and Rescue --- Fixed-wing aircraft and helicopters are
> routinely used in coordination with ground crews to help locate
> missing persons or the site of an accident.
>
> • Aerial Surveillance --- Fixed-wing aircraft and helicopters are
> routinely used to observe ground activity for natural resource
> management, emergency management, and law enforcement purposes.
>
> • Photogrammetry --- Aerial photography can be used to produce highly
> accurate maps. This technique depends on precise knowledge of the
> position of the aircraft and the camera exposure station.
>
> • Surveying --- Geodetic surveying measures the size, shape, and
> gravity field of the earth, and provides the control datums to which
> all other surveys are referenced. Surveying is also used to establish
> property boundaries, provide control points for large construction
> projects, support marine dredging operations and buoy placement,
> measure the physical dynamics of the earth\'s crust, map the relief
> and features of the earth\'s surface, and gather geospatial data (data
> with geographic coordinates).
>
> • Time and Frequency Metrology --- Precise time and frequency
> measurements are required for calibration and synchronization purposes
> by scientific laboratories, deep-space tracking stations and
> astronomical observatories, telecommunication network operators, and
> electrical power utilities.

Requirements for these applications are summarized in Table 2-5.

Table 2-5.  Non-Transportation Positioning/Timing Requirements

+----------------+------------+---------------+----------+-----------+
| Application    | Accuracy   | Time to       | Avai     | Coverage  |
|                |            |               | lability |           |
|                | (2 drms)   | Alarm         |          | Area      |
+----------------+------------+---------------+----------+-----------+
| Remote Sensing | under      | under study   | under    | worldwide |
|                | study      |               | study    |           |
| (space-based)  |            |               |          |           |
+----------------+------------+---------------+----------+-----------+
| Search and     | 10 m       | not specified | not      | n         |
| Rescue         |            |               | s        | ationwide |
|                |            |               | pecified |           |
+----------------+------------+---------------+----------+-----------+
| Aerial         | 1-5 m      | minutes to    | 95-99%   | n         |
| Surveillance   |            | hours         |          | ationwide |
|                |            |               |          | to        |
|                |            |               |          | worldwide |
+----------------+------------+---------------+----------+-----------+
| Photogrammetry | 2-5 cm     | minutes       | not      | n         |
|                |            |               | s        | ationwide |
|                |            |               | pecified |           |
+----------------+------------+---------------+----------+-----------+
| Geodetic       | ho         | hours         | 99%      | sites     |
| Control        | riz:  2-40 |               |          | n         |
| Surveys        | cm         | (data         |          | ationwide |
|                |            | po            |          |           |
|                | vert:  1   | st-processed) |          |           |
|                | cm         |               |          |           |
+----------------+------------+---------------+----------+-----------+
| Boundary       | hori       | hours         | 99%      | sites     |
| Surveys        | z:  0.02-1 |               |          | n         |
|                | m          | (data         |          | ationwide |
|                |            | po            |          |           |
|                | v          | st-processed) |          |           |
|                | ert:  none |               |          |           |
+----------------+------------+---------------+----------+-----------+
| Hydrographic   | h          | hours         | 99%      | waterways |
| Surveys:       | oriz:  1-6 |               |          | n         |
|                | m          | (data         | 99%      | ationwide |
| Offshore       |            | po            |          |           |
| Dredging       | v          | st-processed) | 99%      | waterways |
|                | ert:  4-10 |               |          | n         |
| Inshore        | cm         | hours         | 99%      | ationwide |
| Dredging       |            |               |          |           |
|                | h          | (data         |          | waterways |
| Channel        | oriz:  1-6 | po            |          | n         |
| Conditions     | m          | st-processed) |          | ationwide |
|                | v          |               |          |           |
| Offshore       | ert:  none | hours         |          | waterways |
| Geophysical    |            |               |          | n         |
|                | h          | (data         |          | ationwide |
|                | oriz:  1-6 | po            |          |           |
|                | m          | st-processed) |          |           |
|                |            |               |          |           |
|                | ve         | hours         |          |           |
|                | rt:  10-20 |               |          |           |
|                | cm         | (data         |          |           |
|                |            | po            |          |           |
|                | ho         | st-processed) |          |           |
|                | riz:  2-10 |               |          |           |
|                | m          |               |          |           |
|                |            |               |          |           |
|                | vert:  10  |               |          |           |
|                | cm         |               |          |           |
+----------------+------------+---------------+----------+-----------+
| Deformation    | h          | hours         | 99%      | selected  |
| Surveys        | oriz:  1-2 |               |          | sites     |
|                | mm         | (data         |          | n         |
|                |            | po            |          | ationwide |
|                | vert:  1   | st-processed) |          |           |
|                | mm         |               |          |           |
+----------------+------------+---------------+----------+-----------+
| Topographic    | horiz:  2  | hours         | 99%      | sites     |
| Surveys        | cm         |               |          | n         |
|                |            | (data         |          | ationwide |
|                | vert:  1   | po            |          |           |
|                | cm         | st-processed) |          |           |
+----------------+------------+---------------+----------+-----------+
| Master Plan    | hor        | hours         | 99%      | sites     |
| Mapping        | iz:  0.2-5 |               |          | n         |
|                | m          | (data         |          | ationwide |
|                |            | po            |          |           |
|                | v          | st-processed) |          |           |
|                | ert:  1-20 |               |          |           |
|                | cm         |               |          |           |
+----------------+------------+---------------+----------+-----------+
| Flood Plain    | h          | hours         | 99%      | sites     |
| Mapping        | oriz:  1-5 |               |          | n         |
|                | m          | (data         |          | ationwide |
|                |            | po            |          |           |
|                | v          | st-processed) |          |           |
|                | ert:  1-20 |               |          |           |
|                | cm         |               |          |           |
+----------------+------------+---------------+----------+-----------+
| Resources      | ho         | hours         | 99%      | sites     |
| Mapping        | riz:  1-10 |               |          | n         |
|                | m          | (data         |          | ationwide |
|                |            | po            |          |           |
|                | ve         | st-processed) |          |           |
|                | rt:  0.4-1 |               |          |           |
|                | m          |               |          |           |
+----------------+------------+---------------+----------+-----------+

Table 2-5.  Non-Transportation Positioning/Timing Requirements,
Continued

+----------------+------------+---------------+----------+-----------+
| Hydrology      | ho         | hours         | 99%      | sites     |
| Study          | riz:  1-10 |               |          | n         |
|                | m          | (data         |          | ationwide |
|                |            | po            |          |           |
|                | ve         | st-processed) |          |           |
|                | rt:  20-40 |               |          |           |
|                | cm         |               |          |           |
+----------------+------------+---------------+----------+-----------+
| Emergency      | ho         | minutes       | 99%      | sites     |
| Management     | riz:  8-10 |               |          | n         |
|                | m          |               |          | ationwide |
|                |            |               |          |           |
|                | v          |               |          |           |
|                | ert:  8-10 |               |          |           |
|                | m          |               |          |           |
+----------------+------------+---------------+----------+-----------+
| Time and       | 100        | not specified | not      | worldwide |
| Frequency      | nan        |               | s        |           |
| Metrology      | oseconds\* |               | pecified |           |
+----------------+------------+---------------+----------+-----------+

\*1 sigma, not a 2 drms value.

**2.6  Requirements Summary**

Federal navigation and positioning requirements for accuracy,
time-to-alarm, availability, and coverage area are summarized below and
in Table 2-6:

> **Accuracy**.  The range of accuracy required is from 1 mm to 1000 m.
> The highest accuracy is required for surveying. The FAA requires only
> 1000 m accuracy for en route navigation, but requires 4.1 m (13.5 ft)
> horizontal and 0.6 m (2 ft) vertical accuracy for Category III
> precision approach and landing.
>
> **Time-to-Alarm**.  Requirements range from 1 second for certain land
> transportation applications to hours for post-processing applications.
>
> **Availability**.  Most users have a need for greater than 99.7%
> availability. Some railroad applications require availability of 100%.
> Availability of 100% is not achievable with current GPS technology and
> may require the development and use of systems other than GPS.
>
> **Coverage Area**.  Federal users require nationwide coverage both at
> ground level and in the volume above ground and that portion over the
> oceans which constitute the National Airspace System (NAS). Worldwide
> coverage or a seamless transition to foreign systems is highly
> desired.

Table 2-6.  Summary of Navigation and Positioning Requirements

+------------------+-------------+--------------+----------+----------+
| Mode/Application | Accuracy    | Time to      | Avai     | Coverage |
|                  |             |              | lability |          |
|                  | (2 drms)    | Alarm        |          | Area     |
+------------------+-------------+--------------+----------+----------+
| **Land           | 1-100 m     | 1-15 seconds | 99.7%    | na       |
| T                |             |              |          | tionwide |
| ransportation:** | 1-30 m      | 1-5 seconds  | 9        |          |
|                  |             |              | 9.7-100% | na       |
| IVHS             |             |              |          | tionwide |
|                  |             |              |          |          |
| Railroads        |             |              |          |          |
+------------------+-------------+--------------+----------+----------+
| **Marine         | 8-20 m      | 5-10 seconds | 99-99.9% | na       |
| T                |             |              |          | tionwide |
| ransportation:** |             |              |          | to       |
|                  |             |              |          | w        |
| Harbor           |             |              |          | orldwide |
| Navigation       |             |              |          |          |
+------------------+-------------+--------------+----------+----------+
| **Air            | horiz,      | 2-10 seconds | 99.977   | National |
| T                | vert:  1000 |              | -99.999% | Airspace |
| ransportation:** | m           |              |          |          |
|                  |             |              |          | System   |
| Precision        | to          |              |          |          |
| Approach         |             |              |          |          |
|                  | horiz:  4.1 |              |          |          |
| and Landing      | m           |              |          |          |
|                  |             |              |          |          |
|                  | vert:  0.6  |              |          |          |
|                  | m           |              |          |          |
+------------------+-------------+--------------+----------+----------+
| **Non-T          | 1-5 m       | minutes to   | 95-99%   | na       |
| ransportation:** |             | hours        |          | tionwide |
|                  | 10 m        |              | not      |          |
| Aerial           |             | not          | s        | na       |
| Surveillance     | 2-5 cm      | specified    | pecified | tionwide |
|                  |             |              |          |          |
| Search and       | horiz,      | minutes      | not      | na       |
| Rescue           | vert: 10 m  |              | s        | tionwide |
|                  |             | hours        | pecified |          |
| Photogrammetry   | to          |              |          | na       |
|                  |             | (data        | 99%      | tionwide |
| S                | horiz: 1 cm | pos          |          |          |
| urveying/Mapping |             | t-processed) | not      | w        |
|                  | vert: 1 mm  |              | s        | orldwide |
| Time and         |             | not          | pecified |          |
| Frequency        | 100         | specified    |          |          |
| Metrology        | na          |              |          |          |
|                  | noseconds\* |              |          |          |
+------------------+-------------+--------------+----------+----------+

\*1 sigma, not a 2 drms value.

**3**

**DESCRIPTION OF GPS AND**

**AUGMENTED GPS SYSTEMS**

This section describes basic GPS operation and performance. It also
describes existing or proposed systems which provide correction
information that can be used to augment GPS performance. These
descriptions are not exhaustive and all proposed augmentations to GPS
are not included. The study team targeted those systems with the
potential to meet the widest possible range of user requirements.

**3.1  GPS Standard Positioning Service and Precise Positioning
Service**

GPS is a spaced-based radionavigation system which is operated for the
Federal Government by DOD and jointly managed by DOD and DOT. GPS was
originally developed as a military force enhancement system and will
continue to function in this role. However, GPS also provides
significant benefits to the civilian community. In an effort to make GPS
service available to the greatest number of users while ensuring that
the national security interests of the United States are protected, two
GPS services are provided. The Precise Positioning Service (PPS)
provides full system accuracy primarily to U.S. and allied military
users. The Standard Positioning Service (SPS) provides civilian and all
other users throughout the world with a less accurate positioning
capability than the PPS. A more detailed description of SPS and PPS is
contained in Appendix D.

**3.2  The Need for Augmentation**

GPS offers substantial navigation and positioning capabilities, but SPS
and PPS do not meet many of the user requirements for accuracy, time to
alarm, availability, and coverage that were identified in Section 2.
Numerous systems have been developed or proposed to augment the
performance of GPS to meet the requirements of various users. These
systems provide additional data that are used to compensate for errors
and enhance the capabilities of GPS. For many applications, GPS does not
meet user requirements in three critical areas:

> **Accuracy**.  The requirements of many users and applications require
> substantially better accuracy than can be provided by SPS or even PPS.
> The usefulness of any GPS system, regardless of the applications, will
> be enhanced as accuracy is improved.

**Integrity (Time to Alarm)**.  In many applications, especially those
that involve the safety of life, it is extremely important that the end
user be notified of system failure promptly. In the approach phase of
aircraft flight, a failure notification time of 2 seconds or less is
required to ensure safe operation.

**Availability**.  The availability of the GPS constellation does not
meet all user requirements. Availability of 99.999% is required for some
aviation applications and 100% is specified for railroad collision
avoidance. Safety of life is the reason for these stringent
requirements.

In addition to these critical areas, other important considerations for
augmented GPS systems include the following:

**Coverage Area**.  Users require augmentation data throughout a
specified coverage area, which may range from local to worldwide.

**Security**.  Security refers to both National security and user
safety. National security involves the ability to deny access to the
system for hostile or unauthorized use. Security from a safety
perspective involves vulnerability of the system to interference. Both
aspects of security are described in more detail in Appendix E.

**Cost**.  Cost considerations include purchase and installation of the
system infrastructure, system operation and maintenance, purchase of
user equipment, and any subscriber or service fees.

**Data Link Characteristics**.  Data link characteristics describe the
method and mode of transmission of augmentation data to the user. This
includes radio frequency (RF) spectrum, bandwidth allocation, and
modulation techniques. To date no RF spectrum has been allocated
specifically for GPS augmentations, so individual providers use various
portions of the spectrum. From a spectrum management perspective, there
may be utility in allocating spectrum for GPS augmentation applications.

**Data Format**.  System developers have identified four data formats
for broadcast of augmented GPS data:

> 1\) RTCM SC-104 --- Radio Technical Commission for Maritime Services
> Special Committee 104.
>
> 2\) RTCA-WAAS --- RTCA, Inc., Wide Area Augmentation System (WAAS).
>
> 3\) RTCA-LADGPS --- RTCA, Inc., Local Area Differential GPS (LADGPS).
>
> 4\) Proprietary.

An additional format standard, Receiver Independent Exchange (RINEX), is
used to exchange data for post-processing. Appendix F contains an
analysis and comparison of the RTCM and RTCA data formats.

**Time Frame of Availability**.  GPS system benefits are substantial and
making these benefits available as soon as possible to all potential
users is of great importance. System development and deployment
schedules must be examined and evaluated in light of the benefits that
can be achieved by early deployment of augmentation systems.

**3.3  Functional Descriptions of Augmented GPS Systems**

Of the GPS augmentations developed or proposed, this study focused on
those augmentations which have either been implemented, are likely to be
implemented, or are system concepts that alone or in combination with
other systems have a likelihood of meeting most user requirements. The
augmentations studied included:

1\) Low Frequency (LF)/Medium Frequency (MF) Radiobeacon
System --- broadcasts local augmentation data from beacons in the marine
radionavigation spectrum between 283.5 and 325 kHz. USCG has begun
installing beacons and associated master stations to cover coastal
waters, inland waterways (in conjunction with the U.S. Army Corps of
Engineers), and harbor/harbor approach areas of the U.S.

2\) Commercial Frequency Modulation (FM) Subcarrier
System --- broadcasts local augmentation data from existing
privately-owned FM broadcast radio stations.

3\) Wide Area System (WAS) 1 --- broadcasts augmentation data and a
supplementary ranging signal from geosynchronous Earth orbit (GEO)
satellites on L1 for en route navigation through Category I precision
approach, and broadcasts local augmentation data for Category II/III
precision approach through the LADGPS portion of the system.

4\) WAS 2 --- broadcasts limited augmentation data and a supplementary
ranging signal from GEO satellites on L1 for en route navigation through
non-precision approach, and broadcasts local augmentation data for
Category I/II/III precision approach through the LADGPS portion of the
system.

5\) WAS 3 --- broadcasts augmentation data and a supplementary ranging
signal from GEO satellites on a frequency other than L1 for en route
navigation through Category I precision approach and broadcasts local
augmentation data for Category II/III precision approach through the
LADGPS portion of the system.

6\) WAS 4 --- broadcasts encrypted augmentation data and an encrypted
supplementary ranging signal from GEO satellites on L1 for en route
navigation through Category I precision approach, and broadcasts local
augmentation data for Category II/III precision approach through the
LADGPS portion of the system.

7\) WAS 5 --- broadcasts proprietary augmentation data from a commercial
GEO satellite system.

8\) WAS 6 --- broadcasts proprietary augmentation data from a commercial
low Earth orbit (LEO) satellite system.

9\) Continuously Operating Reference Station (CORS) System --- monitors
GPS signals at precisely surveyed reference sites and stores the data
for post-processing support of local geodetic surveying, mapping,
geographic information systems (GIS), and other applications.

10\) Loran-C System --- broadcasts augmentation data or supplementary
navigation signals from an existing network of LF transmitters that are
used for military and civil radionavigation.

11\) Advanced Communications Technology Satellite (ACTS) --- broadcasts
augmentation data from a satellite using steerable spot beams to
specified geographic areas. The experimental ACTS was launched by the
National Aeronautics and Space Administration (NASA) in September 1993.

12\) Global Orbiting Navigation Satellite System
(GLONASS) --- broadcasts navigation signals from a planned 24 satellite
constellation similar to GPS.

13\) Expanded GPS Constellation --- broadcasts navigation signals from
additional GPS satellites.

14\) Inertial Navigation System (INS) --- provides platform attitude,
position, and velocity information that can be integrated with the GPS
navigation solution.

15\) Sign Post System --- provides position information from electronic
ground-based markers that can be integrated with the GPS navigation
solution.

16\) Pseudolite System --- broadcasts supplementary navigation signals
from ground-based transmitters that imitate a GPS satellite.

17\) Dead Reckoning and Map Matching System --- provides position
information based on measurements of distance and time and comparisons
to a map database to supplement GPS navigation solutions.

18\) Omega System --- broadcasts data from an existing network of very
low frequency (VLF) transmitters used for military and civil navigation,
positioning, and timing.

The study team selected 10 augmented GPS systems from among these
alternatives for detailed evaluation. An eleventh system (listed as
number 2 below) was added which was an expanded version of the LF/MF
radiobeacon system (listed as number 1 above). The selection was based
on technical feasibility, potential for meeting user requirements, and
implementation timetable. The systems selected were:

> 1\) LF/MF Radiobeacon System (coverage over waterways).
>
> 2\) LF/MF Radiobeacon System (expanded to provide complete coverage of
> the U.S.).
>
> 3\) Commercial FM Subcarrier System.
>
> 4\) WAS 1.
>
> 5\) WAS 2.
>
> 6\) WAS 3.
>
> 7\) WAS 4.
>
> 8\) WAS 5.
>
> 9\) WAS 6.
>
> 10\) CORS System.
>
> 11\) Loran-C System.

The following systems were not considered further in this study:

> 1\) ACTS.
>
> 2\) GLONASS.
>
> 3\) GPS Expanded Constellation.
>
> 4\) INS.
>
> 5\) Sign Post System.
>
> 6\) Pseudolite System.
>
> 7\) Dead Reckoning/Map Matching System.
>
> 8\) Omega System.

The rationale for eliminating these systems is provided in the following
paragraphs:

> 1\) ACTS --- Since ACTS has been developed for testing advanced
> communication concepts, it is not likely to provide a feasible
> augmentation scheme in a time frame considered reasonable in this
> study. This system is experimental and does not offer sufficient data
> for evaluation in the decision matrix.
>
> 2\) GLONASS --- This system does not offer a sufficient history of
> reliable operation to guarantee that integrity and availability
> requirements can be met by the GLONASS augmentation to GPS.
>
> 3\) GPS Expanded Constellation --- Insufficient data exist to verify
> the capabilities of this system. This expansion would also be costly
> and would take significant time to implement.

4\) INS --- As a stand-alone augmentation to GPS, INS does not satisfy
the requirements of many Federal users.

5\) Sign Post --- As a stand-alone augmentation to GPS, sign posts do
not satisfy the requirements of many Federal users.

6\) Pseudolite --- Research in the development of pseudolites is
progressing rapidly, but at the time of this study, pseudolites had not
been sufficiently developed to verify their capabilities.

7\) Dead Reckoning/Map Matching --- As a stand-alone augmentation to
GPS, dead reckoning/map matching does not satisfy the requirements of
many Federal users.

8\) Omega --- As a stand-alone augmentation to GPS, Omega does not
satisfy the requirements of many Federal users.

For a further description of some of these systems, see Appendix G.

The 11 selected augmented GPS systems listed above are described below.
The descriptions of these systems address accuracy, integrity (time to
alarm), availability, and the additional considerations detailed in
Section 3.2.

**3.3.1  USCG LF/MF Radiobeacon System**

The USCG broadcasts localized pseudorange corrections from a network of
LF/MF-band marine radiobeacons. The two control centers, one for each
coast of the U.S., will continuously poll the monitor and reference
stations to determine the status and integrity of the broadcast. In case
of technical difficulty, the control centers will resolve the problem
remotely or immediately dispatch technicians to the affected site. A
block diagram of the system is shown in Figure 3-1.

The system is implemented through the existing marine non-directional
beacon infrastructure. The RTCM data format \[6\] is used for the
broadcast of differential GPS (DGPS) corrections and related
information. Normally, the data transmission rate will be 100 bps except
along critical waterways where the transmission rate will be 200 bps.

**Accuracy**.  A horizontal accuracy of 5 m, 2 drms, is specified by
USCG for all coverage areas. However, operating beacons consistently
provide horizontal accuracies of 3 m and although a horizontal system,
vertical accuracy on the order of 5 m can be expected. Continuous
velocity accuracy of the system (vessel speed over ground) is better
than 5 cm/sec (0.1 knots).

**Integrity (Time to Alarm)**.  Based upon the Type 9 message of the
RTCM format and the data rate of 200 bps, the time to alarm is 4.2
seconds.

![](media/image2.wmf){width="5.969444444444444in"
height="6.976388888888889in"}

**Availability**.  Availability of 99.7% is specified in general and
99.9% is specified for critical waterways. This higher availability is
achieved through redundant coverage. The availability may be further
increased by decreasing the distance between reference stations.

**Coverage Area**.  The system is designed to provide coverage for all
harbor/harbor approach areas and other critical waterways for which the
USCG provides aids to navigation. As a result, complete coverage of the
coast line of the continental U.S. (CONUS) is provided and extends out
to 37 km (20 nautical miles). It is expected that in the near future
this coverage will be extended to cover the complete CONUS Coastal
Navigation Zone which extends out to 93 km (50 nautical miles). Figure
3-2 shows the expected coverage area for the system as currently planned
for deployment.

![](media/image3.wmf){width="6.473611111111111in"
height="3.9715277777777778in"}

**Security**.  The system provides the same level of user safety and
security as current marine radionavigation aids. The system does not
employ encryption or any other user screening or security features.

**Infrastructure Cost**.  The total cost for establishing the
operational system of 61 sites is \$14.2M. The annual cost for
operations and maintenance (O&M) is \$4.2M. The total life cycle cost
over 20 years is \$14.2M + 20(\$4.2M) = \$98.2M.

**User Cost**.  Users of the system require a LF/MF radio coupled with a
DGPS-capable receiver. Current cost for low-end equipment is less than
\$1,000.

**Data Link Characteristics**.  The system adds a digitally modulated
minimum shift keying (MSK) subcarrier to transmissions from marine radio
beacons operating in the 283.5 to 325 kHz (LF/MF) band. The LF/MF signal
propagates in the groundwave mode. The signal can be received at ranges
which are well beyond line of sight.

**Data Format**.  The system broadcasts using the RTCM SC-104 format,
Version 2.1. Type 9 messages are used for the GPS differential
corrections. This format is supported by numerous GPS equipment
manufactur­ers and service providers. The RTCM format has been designated
for international maritime use by the International Telecommunication
Union (ITU).

**Time Frame of Availability**.  At least 12 prototype sites are
operating, with a total of 61 planned to be fully operational by January
1996.

**3.3.2  USCG LF/MF Radiobeacon System Expanded**

With the addition of 20 to 50 beacon sites to provide nationwide
coverage, this system is a nationwide expansion of the system described
in Section 3.3.1. All factors described in Section 3.3.1 are identical
except coverage area, infrastructure cost, and time frame of
availability.

**Coverage Area**.  The USCG Expanded (USCG(E)) System is designed to
provide nationwide coverage including harbor/harbor approach areas and
other critical waterways for which the USCG provides aids to navigation.
Figure 3-3 shows the predicted coverage area for 41 additional beacon
sites, and Figure 3-4 shows the predicted composite coverage for the
original 61 beacon sites plus the 41 additional sites. Inland coverage
depends on ground conductivity and the actual number of sites to achieve
nationwide coverage can only be estimated at this time. Appendix H
describes the expected coverage and availability of an LF/MF radiobeacon
system.

**Infrastructure Cost**.  The total cost for establishing the additional
20-50 sites is \$3M to \$8M. The additional annual cost for operations
and maintenance (O&M) is \$1M to \$2M. The maximum total life cycle cost
over 20 years for the USCG(E) system would be \$146M.

**Time Frame of Availability**.  It is expected that the additional 20
to 50 sites will require a total of 1 to 2 years deployment time.

![](media/image4.wmf){width="6.470833333333333in"
height="3.972916666666667in"}

![](media/image5.wmf){width="6.475in" height="3.970833333333333in"}

**3.3.3  Commercial FM Subcarrier System**

This system uses the existing infrastructure of FM radio station
subcarriers to broadcast localized pseudorange correction factors to the
user community. The system consists of a GPS reference station and one
or more FM stations which broadcast the GPS corrections. A block diagram
of a typical FM subcarrier system is shown in Figure 3-5. Companies
providing FM subcarrier DGPS service currently contract with 300 to 400
FM stations across the Nation.

**Accuracy**.  The accuracy provided by these types of services depends,
in part, upon the level of service required and paid for by the user.
Service providers offer a variety of accuracy options for the user
ranging from 1 to 3 meters to several tens of meters.

**Integrity (Time to Alarm)**. FM subcarrier systems can include
integrity monitors to continuously validate that corrections remain
within specified tolerances. Although current systems do not necessarily
provide real-time integrity monitoring, this function is technically
achievable.

**Availability**. Availability is a function of the maintenance schedule
or the failure of independently-managed broadcast stations, the GPS
reference stations, and the various data links involved. The broadcast
stations used are those that operate 24 hours a day and have redundant
equipment including backup power and alternate transmitters to ensure
that scheduled maintenance will not generally result in an outage. The
National Association of Broadcasters does not have statistics regarding
FM station availability; however, it asserts that most stations do
better than one hour outage per year (99.988%). FM stations have a
strong financial incentive to stay operational and many stations have
been on the air continuously for years. A conservative estimate predicts
one day of down time every 10 years resulting in an availability of
99.97%.

**Coverage Area**.  FM Broadcast stations cover 96% of the population
and 80% of the land area of North America \[7\]. The coverage area of an
entire subcarrier system depends upon the contractual arrangements made
by the operator of the system, percent injection of the subcarrier and
receiver capabilities. An example of subcarrier coverage using many
Public Broadcasting System (PBS) stations for CONUS is shown in Figure
3-6.

**Security**.  FM subcarrier systems are encrypted in order to provide a
means of controlling user access to system services.

**Infrastructure Cost**.  The infrastructure costs are borne by the
service provider.

**User Cost**.  User costs include the purchase of receiver equipment
and the user service fee. User equipment for this architecture is
expected to cost on the order of \$500 or less and may have service fees
on the order of a few dollars per day.

![](media/image6.wmf){width="5.972222222222222in"
height="6.976388888888889in"}

![](media/image7.wmf){width="6.475in" height="3.973611111111111in"}

**Data Link Characteristics**.  These systems use the Radio Data Systems
(RDS) or Radio Broadcast Data Systems (RBDS-US) standard for the
transmission of digital data using subcarrier modulation on broadcast FM
radio stations. GPS correction data are multiplexed with other user
services which are also placed on the FM subcarrier.

**Data Format**.  A proprietary data format is used for this system. The
data is translated to RTCM format to make it compatible with existing
DGPS receivers. The subcarrier data structures used meet standards for
FM broadcast in most countries. Other subcarrier structures can be used
by these systems.

**Time Frame of Availability**.  FM subcarrier services and systems are
operational at the present time. All providers plan system and service
expansions as user demands require.

**3.3.4  Wide Area System 1**

The Wide Area System 1 (WAS 1) has two components, FAA\'s Wide Area
Augmentation System (WAAS) and a local area DGPS (LADGPS) system. The
WAAS component satisfies accuracy, time to alarm, and availability
requirements for all phases of flight down to Category I precision
approach. Category II and III precision approach requirements are
satisfied by the LADGPS component of the system.

**3.3.4.1  FAA WAAS**

The FAA WAAS as currently planned consists of GEO communication
satellites, wide area reference stations (WRSs), and wide area master
stations (WMSs). The GEO satellites provide ranging signals and
broadcast integrity and differential correction data. GPS satellite data
are received and processed at widely dispersed WRSs. These data are
forwarded to WMSs, which process the data to determine the differential
corrections. GEO satellites downlink these data on the GPS L1 frequency
with a modulation similar to that used by GPS.

The GEOs not only provide the WAAS information on each GPS satellite and
the ionosphere, but act as additional ranging sources. Figure 3-7 is a
block diagram of the FAA WAAS system.

**Accuracy**.  The accuracy specified for the WAAS is 7.6 meters (95%)
both horizontal and vertical \[8\].

**Integrity**.  Integrity for the WAAS is specified in terms of
probability of hazardously misleading information (HMI), time to alarm,
and alarm limit. This definition of integrity is more developed than
that defined for other systems since the specification for FAA
applications are more demanding. For the en route through nonprecision
approach operations, the WAAS specification for probability of HMI is
10^-7^ per hour; the time to alarm specified is 8 seconds; and the alarm
limit is 556 meters (horizontal error) for a total system error. For the
precision approach operation, the WAAS specification for probability of
HMI is 4 x 10^-8^ per approach; the time to alarm specified is 5.2
seconds; and the alarm limit is the same as for the en route through
nonprecision approach operation.

**Availability**.  The availability of the WAAS is specified as 99.999%.

**Coverage**.  The specified service volume is from the surface to
30,500 meters (100,000 feet) above sea level over the contiguous U.S.,
Alaska, Hawaii, Puerto Rico, the Pacific Ocean to Hawaii, the Atlantic
Ocean off the coast of the U.S., and much of the Gulf of Mexico. This
coverage is the footprint of the GEO satellite(s).

**Security**.  This system does not use encryption methods, user access
controls, or other screening.

**Infrastructure Cost**.  The WAAS life cycle cost is estimated to be on
the order of \$1,139M.

**User Cost**.  User equipment (avionics) for this architecture is
expected to cost on the order of \$4K for general aviation aircraft to
\$90K for commercial air carriers.

![](media/image8.wmf){width="5.972222222222222in"
height="7.726388888888889in"}

**Data Link Characteristics**.  The WAAS satellites will broadcast a
GPS-like spread spectrum signal on the GPS L1 frequency. The effective
data rate is 250 bps versus 50 bps for GPS. The satellite navigation
message will contain WAAS data (integrity data and differential
corrections for accuracy), as well as navigation data so that the
satellite can be a ranging source.

**Data Format**.  The WAAS portion of the data link will use the RTCA,
Inc. WAAS format \[9\].

**Time Frame of Availability**.  The Phase 1 portion of WAAS, which will
provide integrity and availability, is scheduled to be operational by
the end of 1997. The Phase 2 portion of WAAS, the accuracy component, is
scheduled to be implemented by 1998.

**3.3.4.2 FAA LADGPS System**

Local area systems serve airports near the reference station that
gathers GPS data and determines differen­tial corrections. A generic
local area differential ground system would consist of a ground monitor
system that would determine corrections and integrity, and a
communications system that would transmit correction and integrity data
to aircraft. FAA is conducting a feasibility program to determine if a
local area DGPS system can meet the requirements for Category II/III
precision approaches and landings. The results of this study are
expected in fiscal year 1995. Figure 3-8 shows an example of a proposed
FAA local area system. This system will be designed to meet all
requirements for the Category II/III precision approach phase of flight.

**3.3.5  Wide Area System 2**

Wide Area System 2 (WAS 2) is a variation of WAS 1. It differs in that
the WAAS portion provides enhancements to integrity and availability
only. Pseudorange correction information is not transmitted from the GEO
satellites. This change minimizes national security risks, but it
requires additional LADGPS systems to provide the increased accuracy
required for Category I precision approaches. LADGPS systems must also
be implemented for the Category II and III precision approaches as in
WAS 1.

LADGPS systems must be implemented to provide the increased accuracy
required for Category I as well as Category II and III precision
approaches supported in WAS 1. This system, therefore, includes the
implementation of approximately 620 Category I LADGPS systems in
addition to the 150 LADGPS systems needed to support Category II/III
operations. FAA is considering two alternatives for the acquisition of
the required Category I LADGPS systems: Special Category I (SCAT I) and
publicly funded Category I systems.

![](media/image9.wmf){width="5.972222222222222in"
height="6.976388888888889in"}

SCAT I systems would be developed and acquired, under FAA supervision
and approval, by private industry for specific users. SCAT I systems are
expected to be limited to a relatively small number of selected
locations. The majority of the Category I LADGPS system requirements
would be satisfied by systems developed and funded by the FAA. Both SCAT
I and public Category I LADGPS systems would be specified to meet
operational requirements associated with Category I precision approach
operations.

**Accuracy**.  The accuracies provided by the WAAS portion of WAS 2 are
the SPS accuracies of 100 meters horizontal, 156 meters vertical. The
specification for accuracy of the LADGPS system will meet the
requirements defined for the precision approach phase of flight.

**Integrity**.  The integrity enhancement provided by WAS 2 is the same
as that provided by WAS 1.

**Availability**.  The availability enhancement provided by WAS 2 is the
same as that provided by WAS 1.

**Coverage**. The WAAS portion of WAS 2 does not provide pseudorange
correction information. Integrity and availability information are
provided over the footprint of the GEO satellite. The accuracy
requirements for the precision approaches are provided within the
coverage area of the LADGPS systems. It is expected that under WAS 2, an
estimated 620 more LADGPS systems would be installed than under WAS 1 to
support Category I precision approach requirements.

**Security**.  This system does not plan to use encryption methods, user
access controls, or other screening.

**Infrastructure Cost**.  The estimated life cycle cost of the WAAS
portion of WAS 2 is \$670M. The estimated life cycle cost for the 620
Category I LADGPS systems is \$560M. The estimated cost of the more
sophisticated Category II/III LADGPS systems remains the same as in WAS
1, \$195M. The total estimated life cycle cost for WAS 2 is \$1,425M.

**User Cost**.  User equipment (avionics) for this architecture is
expected to cost on the order of \$4.4K for general aviation aircraft to
\$99K for commercial air carriers.

**Data Link Characteristics**.  The WAAS satellites will broadcast a
GPS-like spread spectrum signal on the GPS L1 frequency. The effective
data rate is 250 bps. The satellite navigation message will contain
integrity data and navigation data so that the satellite can be a
ranging source. No operational data link requirements are specified as
yet for the LADGPS systems. Options for the data link include Mode-S,
VHF, and L1.

**Data Format**.  The WAAS portion of the data link will use the RTCA
WAAS format. The LADGPS portion of this system will use the RTCA LADGPS
format.

**Time Frame of Availability**.  The WAAS portion of WAS 2, which
includes integrity and availability components only, is expected to be
available in the same time frame as the WAAS portion of WAS 1 --- by
1997. The LADGPS portion of WAS 2 is expected to take an additional 2 to
3 years, predicated on the availability of funding.

**3.3.6  Wide Area System 3**

Wide Area System 3 (WAS 3) is another variation of WAS 1, with
augmentation data transmitted from a communications satellite using a
frequency other than L1.

**Accuracy**.  The accuracy enhancement provided by the WAAS portion of
WAS 3 is the same as that provided by the WAAS portion of WAS 1: 7.6
meters (95%) both horizontal and vertical. The accuracy enhancement
provided by the LADGPS portion of WAS 3 is the same as that provided by
the LADGPS portion of WAS 1: meets the requirements defined for the
Category II/III precision approach phase of flight.

**Integrity**.  The integrity enhancement provided by the WAAS portion
of WAS 3 is the same as that provided by WAS 1: the probability of HMI
is 10^-7^ per hour; the time to alarm is 8 seconds; and the alarm limit
is 556 meters (horizontal error) for a total system error. For the
precision approach operation, the WAAS requirements for probability of
HMI is 4 x 10^-8^ per approach; the time to alarm is 5.2 seconds; and
the alarm limit is the same as for the en route through nonprecision
approach operation. The integrity enhancement provided by the LADGPS
portion of WAS 3 is the same as that provided by WAS 1: meets the
requirements defined for the Category II/III precision approach phase of
flight.

**Availability**.  The availability enhancement provided by the WAAS
portion of WAS 3 is the same as that provided by WAS 1: 99.999%. The
availability enhancement provided by the LADGPS portion of WAS 3 is the
same as that provided by WAS 1: meets the requirements defined for the
Category II/III precision approach phase of flight.

**Coverage**.  The coverage provided by the WAAS portion of WAS 3 is the
same as that provided by WAS 1: from the surface to 30,500 meters
(100,000 feet) above sea level over the contiguous U.S., Alaska, Hawaii,
Puerto Rico, the Pacific Ocean to Hawaii, the Atlantic Ocean off the
coast of the U.S., and much of the Gulf of Mexico. The coverage provided
by the LADGPS portion of WAS 3 is the same as that provided by WAS 1,
but it has not yet been specified.

**Security**. This system does not plan to use encryption methods, user
access controls or other screening.

**Infrastructure Cost**.  WAS 3 design remains conceptual, but it is
assumed that the life cycle cost for the WAAS portion of the system will
remain the same as for WAS 1, \$1,139M. The estimated life cycle cost
for the Category II/III LADGPS systems also remains the same at \$195M.
The total life cycle cost would be approximately \$1,334M.

**User Cost**.  The cost of avionics equipment for WAS 3 is expected to
be approximately \$4.4K for general aviation users and \$99K for
commercial air carriers.

**Data Link Characteristics**.  As in WAS 1, the WAAS portion of WAS 3
will transmit integrity, availability and accuracy information from a
communications satellite, but on a frequency other than L1. The data
link characteristics for the transmission of accuracy information are
not yet known for WAS 3, because a specific frequency, modulation
scheme, and transmitter location (satellite) have not been determined.
LADGPS system data transmission will be the same as for WAS 1, and is
not yet defined. Options for the data link include Mode-S, VHF, L1, or
the WAS 3 WAAS frequency.

**Data Format**.  The data format implemented in WAS 3 is the same as
that implemented in WAS 1 and is based on the RTCA standard. The LADGPS
portion of this system will use the RTCA LADGPS format.

**Time Frame of Availability**.  The WAS 3 system remains conceptual,
and considerable design work is required before implementation could
begin. It is expected that this system could not be operational until at
least 1998.

**3.3.7  Wide Area System 4**

In order to maximize the use of GPS without sacrificing National or user
security, the GPS Joint Program Office (JPO) has proposed an Augmented
GPS (AGPS) System with the following characteristics:

> • One common network of systems all receiving data from the AGPS
> System.
>
> • All AGPS links encrypted.
>
> • DOT provides a master decryption key to the service providers and
> manages access to the AGPS System.
>
> • Service providers licensed. Value added services could be provided
> to their users as seen fit. Providers distribute decryption keys to
> users.

**Accuracy, Integrity, Availability, and Coverage**.  Since the service
providers decrypt the AGPS signal and provide further services to the
user, accuracy, integrity, availability, and coverage capabilities are
largely at the control of the service provider. The augmented services
can be through the infrastructure provided by the service provider.
Nominally, the capabilities of the AGPS System would be similar to WAS 1
and WAS 3.

**Security**.  This system plans to use encryption methods and user
access controls.

**Infrastructure Cost**.  The estimated cost addition to WAS 1 for WAS 4
enhancements is \$300M. The total life cycle cost of WAS 4 is estimated
at approximately \$1,634M.

**User Cost**.  User costs will depend upon the equipment costs and the
service charges from the service provider. The U.S. government may or
may not charge additional fees for providing the base AGPS System. User
costs are expected to be higher for WAS 4, but exact costs are not
possible to determine at this time.

**Data Link Characteristics**.  This system is based primarily on the
WAS 1 structure. Data link characteristics will be the same as those for
WAS 1, with the addition that all data links will be encrypted.

**Data Format**.  Encryption formats are not yet defined for this
system. User receiver equipment provided by service providers would be
able to decrypt the AGPS signal and provide any data format required by
the user.

**Time Frame of Availability**.  An estimate of system availability is
1998.

**3.3.8  Wide Area System 5**

A number of commercial GEO satellite systems have been developed by
private industry to provide positioning services. At the present time,
navigation services are not provided. These systems typically use
reference stations which send data to a central control facility. The
control center continuously monitors the status of the DGPS network and
quality of the data.

**Accuracy**.  Commercial systems can achieve horizontal accuracies of
0.6 m (2 drms).

**Integrity**.  Although measures have been taken to ensure data
quality, integrity has not been quantified by the commercial service
providers.

**Availability**.  Availability has been recently measured at 99.99%.

**Coverage Area**.  The coverage area of the system depends upon the
satellite(s) used. Coverage area is typical of that provided by other
GEO satellite systems previously discussed.

**Security**.  Commercial GEO satellite systems use encryption and user
access controls.

**Infrastructure Cost**.  All infrastructure costs are borne by the
service provider.

**User Cost**.  User costs involve the acquisition of receivers and user
fees for service. User fees for these systems range from dollars per day
to hundreds of dollars per day.

**Data Link Characteristics**.  The commercial GEO satellite systems
broadcast encrypted data on frequency bands other than L1, for example,
C band.

**Data Format**.  Standard formats, such as the RTCM format, are
supported by the commercial systems; however, the signals are converted
into proprietary data formats for transmission.

**Time Frame of Availability**.  There are commercial systems currently
available.

**3.3.9  Wide Area System 6**

Currently there are no commercial LEO satellite systems available;
however, several different systems, in different stages of development,
have been proposed. Depending on the system, anywhere from 36 to over
100 satellites in low earth orbit constellations have been proposed.
These communications satellites would provide accuracy and integrity
data to users. With these proposed systems, 100% global communications
can be provided.

Some options for disseminating integrity and differential correction
data from LEO satellite systems are:

> • Phone access. Users make a phone call and retrieve data as required
> (positioning applications).
>
> • Continuous broadcasting on a frequency in the S, L, or another band.

**Accuracy**.  It is estimated that a LEO satellite system could provide
1 meter horizontal (2 drms) and 3 meter vertical accuracy.

**Integrity**.  System providers estimate a 6 second time to alarm for
LEO satellite systems.

**Availability**.  LEO satellite systems should provide availability
similar to GEO satellite systems (99.99%); however, since these systems
are only proposed, availability cannot be measured.

**Coverage Area**.  Proposed systems will provide global coverage.

**Security**.  Each LEO satellite will cover a limited geographic
footprint. There could be control of the coverage within each footprint.
Commercial LEO satellite systems will use encryption and user access
controls.

**Infrastructure Cost**.  Infrastructure costs will be borne by the
service provider.

**User Cost**.  User costs involve the acquisition of receivers and user
fees for service. Typical user fees for these systems will be slightly
greater than premium phone services. Typical user equipment will cost
under \$1000 per unit.

**Data Link Characteristics**.  Depending on the user service, LEO
satellite systems will support a wide variety of bands, bandwidths, and
multiplexing schemes.

**Data Formats**.  Receiver equipment will be designed to provide any
data format required by the user. Broadcast formats will be proprietary.

**Time Frame of Availability**. Since these are all proposed systems,
the time frame of availability will be after 1998.

**3.3.10  Continuously Operating Reference Station System**

Continuously operating reference stations (CORS) provide a standardized
means for recording a set of GPS observables, which includes both
carrier phase and code range information. CORS have standardized GPS
receivers and data storage media, and they allow remote system access.
CORS serve post-processing applications and are not real time. To
promote multi-agency use of existing reference stations and to preclude
establishing redundant reference stations, CORS capability may be built
into any reference station. A prototype CORS is operational. Appendix G
contains a further description of the CORS system.

**Accuracy**.  CORS provide observations to support two levels of
accuracy: 1 cm and 1 m.

**Integrity**.  Integrity is derived from post-mission processing.

**Availability**.  CORS can provide 99.0% post-processing data
availability.

**Coverage Area**.  Provided both L1 and L2 data are available, CORS can
provide post-processed accuracies at the 1 cm level using carrier phase
and at the 1 m level using code range. These accuracies are available
for locations up to hundreds of kilometers from the reference site. Note
that CORS provide only a post-processing capability. Other systems have
been developed that can provide real time centimeter accuracies.
Currently, such systems have a range of 10 to 20 km.

**Security**.  CORS provide post-mission capabilities and do not provide
real time navigation. No encryption or limited user access is built into
CORS specifications.

**Infrastructure Cost**.  FAA WAAS reference stations will be designed
to comply with the CORS standard. The USCG reference stations can be
made to comply with the CORS standard at a cost estimated to be less
than \$10K per station. An entirely new CORS for surveying applications
can cost from \$70K to \$150K, depending upon the quality of the
equipment needed for the application.

**User Cost**.  With CORS, survey users no longer require their own
reference station, which, because of productivity gains, can result in a
net savings to the user. The cost of survey equipment can range from the
low thousands to several tens of thousands of dollars. At the present
time, there is no expectation that there will be a charge for access to
archived data.

**Data Link Characteristics**.  There is no direct broadcast data link
to users as part of CORS.

**Data Format**.  It is expected that a CORS will archive data in the
receiver manufacturers\' raw formats. The CORS central facility will
provide data in the RINEX format in order to provide data to users
independent of the equipment used.

**Time Frame of Availability**.  A prototype CORS is currently
operational.

**3.3.11  Loran-C System**

Loran‑C is a low frequency radionavigation system. Loran‑C chains
consist of stations located several hundreds of miles apart. These
chains are located in the U.S. and in various parts of the world.

Loran-C offers three possible solutions to augment GPS:

> • Loran-C used as a data link to transmit DGPS corrections.
>
> • Loran-C calibrated by DGPS. This improved Loran-C system can then be
> used in the event of GPS outages or in a hybrid position solution.
>
> • Loran-C used as an additional ranging signal or pseudolite. This use
> results in increased availability of a navigation solution.

**Accuracy**.  The predictable accuracy of Loran‑C is 460 meters (0.25
nautical miles) 2 drms. Calibration of Loran-C with DGPS can provide a
position accuracy of approximately 5 meters.

**Integrity**.  Loran-C stations are manned and signals are monitored.
Since Loran-C is a very different communications/navigation system from
GPS, a disruption in either GPS or Loran-C is unlikely to disrupt the
other system. Integrated GPS and Loran-C provide the user with two
independent, yet cooperative, navigation capabilities which increase the
overall usefulness of the mixed system. With the inclusion of monitoring
equipment at Loran-C sites, users can be notified of system integrity
problems within 2 seconds.

**Availability**.  Loran-C availability is reported to be 99.75%.
Results from analyses done by the Volpe National Transportation Systems
Center indicate that availability from the combination of GPS with
Receiver Autonomous Integrity Monitoring (RAIM) and Loran-C can exceed
99.99% \[10\].

**Coverage Area**.  Loran-C provides complete coverage of CONUS and
parts of Alaska, western Canada, western Europe, Japan, and parts of
China. Figure 3-9 shows the coverage provided by U.S.-operated or
-supported Loran-C stations.

![](media/image10.wmf){width="6.497916666666667in"
height="2.0597222222222222in"}

**Security**.  Loran-C does not use encryption or any methods for
controlling user access.

**Infrastructure Cost**.  Infrastructure costs to modify existing
Loran-C sites to transmit differential corrections are estimated to be
\$100K per station. The cost of building a new Loran-C site is estimated
at \$8M to \$10M. Loran-C sites will need upgrades within the next few
years to replace aging equipment. The cost of upgrading an existing
Loran site to include solid-state equipment is estimated at \$5M.

**User Cost**.  While there is an existing stock of Loran-C receivers,
new receivers would be required to meet combined GPS/Loran-C
capabilities. While FAA-certified equipment for air navigation could
cost less than \$1,000 per unit, the cost of installing and inspecting a
unit in an aircraft would bring the cost to several thousand dollars per
unit. However, the cost of portable GPS/Loran-C units for non-navigation
uses, such as for ground vehicles, is expected to be less than \$1,000.

**Data Link Characteristics**.  The Loran-C system is centered at 100
kHz and could transmit differential GPS data by time-shifting the
Loran-C bursts. This technique results in a data rate of up to 30 bps.

**Data Format**.  To overcome the low data rates inherent in a Loran-C
differential GPS system, a fully asynchronous message format is
proposed. Every satellite correction would be transmitted in a single
compressed message.

**Time Frame of Availability**.  The basic Loran-C infrastructure is in
place. Modifications and implementation schedules could not meet a date
prior to 1998.

**4**

**EVALUATION OF AUGMENTED GPS SYSTEMS**

This section compares the technical capabilities of the 11 systems
described in Section 3 with the user requirements identified in Section
2. An analytical decision matrix was developed to assist in determining
the final recommendations of this study. The matrix served as a guide in
evaluating the augmented GPS systems and architectures that were
considered but did not provide an absolute solution to determine the
most capable augmented GPS architecture. The decision matrix consisted
of two stages. The first stage, the use of which is illustrated in
Tables 4-1 through 4-22, is the Technical Capabilities Evaluation.
During this stage, user requirements and augmented GPS system
performance specifications were tabulated.

The 11 systems evaluated were:

> 1\) U.S. Coast Guard (USCG) --- This system employs LF/MF beacons and
> is currently being deployed by USCG and the U.S. Army Corps of
> Engineers to provide coverage of U.S. coasts, harbors, harbor
> approaches, and inland waterways.
>
> 2\) U.S. Coast Guard, Expanded (USCG(E)) --- This system expands the
> USCG LF/MF beacon system to provide nationwide coverage.
>
> 3\) FM Subcarrier (FM) --- The FM subcarrier system provides
> differential corrections using the subcarriers of FM broadcast
> stations.
>
> 4\) Wide Area System 1 (WAS 1) --- This system is composed of the FAA
> GEO satellite-based Wide Area Augmentation System (WAAS) to meet the
> integrity, availability, and accuracy requirements of aviation users
> for the en route through Category I precision approach phases of
> flight and approximately 150 local area differential GPS (LADGPS)
> systems for Category II/III precision approach requirements.
>
> 5\) Wide Area System 2 (WAS 2) --- This system is composed of the FAA
> WAAS to meet the requirements of aviation users for the en route
> through non-precision approach phases of flight. In addition to the
> WAAS, approximately 770 LADGPS systems are needed for Category
> I/II/III approach requirements. In this system, the WAAS provides
> integrity and availability only; it does not provide accuracy
> corrections.
>
> 6\) Wide Area System 3 (WAS 3) --- This system is the same as WAS 1
> except that a frequency other than L1 is used to provide differential
> corrections.

7\) Wide Area System 4 (WAS 4) --- This system is the same as WAS 1
except that all communication links are encrypted to provide signal
security.

8\) Wide Area System 5 (WAS 5) --- This is a GEO satellite-based system
provided by private industry.

9\) Wide Area System 6 (WAS 6) --- This is a LEO satellite-based system
provided by private industry.

10\) Continuously Operating Reference Stations (CORS) --- This system is
designed and will be deployed throughout the country to meet the
post-processing requirements of GPS users.

11\) Loran-C --- This system uses Loran-C as a communications link to
provide differential corrections.

**4.1  System Technical Capabilities**

The technical capabilities of the 11 systems described in Section 3 are
summarized in Table 4-1. Some of the parameters used in Section 3 to
describe the systems are not included in the table. Parameters were
excluded if system suppliers did not provide a specification for that
parameter, system performance could not be evaluated, or the parameter
did not provide discrimination between systems. A detailed justification
for Table 4-1 entries is provided in Appendix I.

**4.2  Capabilities Versus Requirements**

Tables 4-2 through 4-17 display the degree to which each of the 11
systems satisfy user requirements. Each mode and phase of operation
identified in Section 2 is compared in a separate table. Each block in
these tables indicates a \"YES\" if the system specification meets or
exceeds the required value and a \"NO\" if the specification does not
meet the requirement. These tables provide an evaluation of the
technical capabilities of each system for each mode and phase of
operation.

Table 4-1. Augmented GPS System Capabilities

<table style="width:100%;">
<colgroup>
<col style="width: 17%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Units</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS*</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Nationwide</p></td>
<td>yes or no</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td><p>Coverage Area—</p>
<p>Ocean</p></td>
<td>yes or no</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Coastal</p></td>
<td>yes or no</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="odd">
<td><p>Coverage—</p>
<p>National Airspace System</p></td>
<td>yes or no</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td>Availability</td>
<td>%</td>
<td>99.70%</td>
<td>99.70%</td>
<td>99.97%</td>
<td>99.999%</td>
<td>99.999%</td>
<td>99.999%</td>
<td>99.999%</td>
<td>99.99%</td>
<td>99.99%</td>
<td>99.00%</td>
<td>99.75%</td>
</tr>
<tr class="odd">
<td>Failure Notification Time</td>
<td>sec</td>
<td>4.2</td>
<td>4.2</td>
<td>3.0</td>
<td>2.0</td>
<td>2.0</td>
<td>2.0</td>
<td>2.0</td>
<td>2.0</td>
<td>6.0</td>
<td>**</td>
<td>2.0</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>meters,</p>
<p>2drms</p></td>
<td>3.0</td>
<td>3.0</td>
<td>1.0</td>
<td>4.1</td>
<td>4.1</td>
<td>4.1</td>
<td>4.1</td>
<td>0.6</td>
<td>1.0</td>
<td>0.001</td>
<td>5.0</td>
</tr>
<tr class="odd">
<td><p>Predictable Accuracy—</p>
<p>Vertical</p></td>
<td><p>meters,</p>
<p>2 sigma</p></td>
<td>4.5</td>
<td>4.5</td>
<td>1.5</td>
<td>0.6</td>
<td>0.6</td>
<td>0.6</td>
<td>0.6</td>
<td>1.0</td>
<td>3.0</td>
<td>0.001</td>
<td>7.5</td>
</tr>
<tr class="even">
<td>Probability of Accuracy and Integrity</td>
<td>1/hour</td>
<td>**</td>
<td>**</td>
<td>**</td>
<td>0.0000001</td>
<td>0.0000001</td>
<td>0.0000001</td>
<td>0.0000001</td>
<td>**</td>
<td>**</td>
<td>**</td>
<td>**</td>
</tr>
<tr class="odd">
<td>Initial Operating Capability</td>
<td>year</td>
<td>1994</td>
<td>1998</td>
<td>1994</td>
<td>1997</td>
<td>1997</td>
<td>&gt;1998</td>
<td>&gt;1998</td>
<td>1994</td>
<td>1998</td>
<td>1994</td>
<td>&gt;1998</td>
</tr>
</tbody>
</table>

\* CORS is not a real-time system.

\*\* Not specified for this system.

Table 4-2. Augmented GPS System Evaluation, Aviation, Oceanic En Route

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Ocean</p></td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.977%</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
</tr>
<tr class="even">
<td>Failure Notification Time</td>
<td>10 sec</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Probability of Accuracy and Integrity (1/hour)</td>
<td>0.0000001</td>
<td rowspan="2">NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
</tr>
</tbody>
</table>

Table 4-3. Augmented GPS System Evaluation, Aviation, Domestic En Route

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>National Airspace Sys.</p></td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.977%</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
</tr>
<tr class="even">
<td>Failure Notification Time</td>
<td>10 sec</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Probability of Accuracy and Integrity (1/hour)</td>
<td>0.0000001</td>
<td rowspan="2">NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
</tr>
</tbody>
</table>

Table 4-4. Augmented GPS System Evaluation, Aviation, Terminal

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Ocean</p></td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
</tr>
<tr class="odd">
<td><p>Coverage Area—</p>
<p>National Airspace Sys.</p></td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td>Availability</td>
<td>99.977%</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
</tr>
<tr class="odd">
<td>Failure Notification Time</td>
<td>10 sec</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td>Probability of Accuracy and Integrity (1/hour)</td>
<td>0.0000001</td>
<td rowspan="2">NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="odd">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
</tr>
</tbody>
</table>

Table 4-5. Augmented GPS System Evaluation, Aviation, Non-precision
Approach and Landing

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Ocean</p></td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
</tr>
<tr class="odd">
<td><p>Coverage Area—</p>
<p>National Airspace Sys.</p></td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td>Availability</td>
<td>99.977%</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
</tr>
<tr class="odd">
<td>Failure Notification Time</td>
<td>10 sec</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td>Probability of Accuracy and Integrity (1/hour)</td>
<td>0.0000001</td>
<td rowspan="2">NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="odd">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
</tr>
</tbody>
</table>

Table 4-6. Augmented GPS System Evaluation, Aviation, Category I
Precision Approach and Landing

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>National Airspace Sys.</p></td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.99%</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
</tr>
<tr class="even">
<td>Failure Notification Time</td>
<td>6 sec</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Probability of Accuracy and Integrity (1/hour)</td>
<td>0.00000004</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>9 meters,</p>
<p>2drms</p></td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td><p>Predictable Accuracy—</p>
<p>Vertical</p></td>
<td><p>3 meters,</p>
<p>2 sigma</p></td>
<td rowspan="2">NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
</tr>
<tr class="even">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
</tr>
</tbody>
</table>

Table 4-7. Augmented GPS System Evaluation, Marine, Harbor/Harbor
Approach

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Coastal</p></td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.7%</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>8 meters,</p>
<p>2drms</p></td>
<td rowspan="2">YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td colspan="2">Meets Requirements</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
</tr>
</tbody>
</table>

Table 4-8. Augmented GPS System Evaluation, Marine, Coastal

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Coastal</p></td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.7%</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>460 meters,</p>
<p>2drms</p></td>
<td rowspan="2">YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td colspan="2">Meets Requirements</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
</tr>
</tbody>
</table>

Table 4-9. Augmented GPS System Evaluation, Marine, Ocean

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Ocean</p></td>
<td>YES</td>
<td>YES*</td>
<td>YES*</td>
<td>YES*</td>
<td>YES*</td>
<td>YES*</td>
<td>YES*</td>
<td>YES*</td>
<td>YES*</td>
<td>YES*</td>
<td>YES*</td>
<td>YES*</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.0%</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>1800 meters,</p>
<p>2drms</p></td>
<td rowspan="2">YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td colspan="2">Meets Requirements</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
</tbody>
</table>

\* Met by SPS.

Table 4-10. Augmented GPS System Evaluation, Land, Highway

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Nationwide</p></td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.7%</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>5 meters,</p>
<p>2drms</p></td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Failure Notification Time</td>
<td>15 sec</td>
<td rowspan="2">YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
</tr>
</tbody>
</table>

Table 4-11. Augmented GPS System Evaluation, Land, Highway (Collision
Avoidance)

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Nationwide</p></td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.7%</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>1 meter,</p>
<p>2drms</p></td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
</tr>
<tr class="odd">
<td>Failure Notification Time</td>
<td>15 sec</td>
<td rowspan="2">YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
</tr>
</tbody>
</table>

Table 4-12. Augmented GPS System Evaluation, Land, Railroad

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Nationwide</p></td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.7%</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>10 meters,</p>
<p>2drms</p></td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Failure Notification Time</td>
<td>5 sec</td>
<td rowspan="2">YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
</tr>
</tbody>
</table>

Table 4-13. Augmented GPS System Evaluation, Land, Railroad (Control)

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Nationwide</p></td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>100%</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>1 meter,</p>
<p>2drms</p></td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
</tr>
<tr class="odd">
<td>Failure Notification Time</td>
<td>5 sec</td>
<td rowspan="2">YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
</tr>
<tr class="even">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
</tr>
</tbody>
</table>

Table 4-14. Augmented GPS System Evaluation, Survey, Land

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Nationwide</p></td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.0%</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>0.02 meters,</p>
<p>2drms</p></td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
</tr>
<tr class="odd">
<td><p>Predictable Accuracy—</p>
<p>Vertical</p></td>
<td><p>0.01 meters,</p>
<p>2 sigma</p></td>
<td rowspan="2">NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
</tr>
<tr class="even">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
</tr>
</tbody>
</table>

Table 4-15. Augmented GPS System Evaluation, Survey, Hydro

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 8%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Nationwide</p></td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.0%</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>1 meter,</p>
<p>2drms</p></td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
</tr>
<tr class="odd">
<td><p>Predictable Accuracy—</p>
<p>Vertical</p></td>
<td><p>0.04 meters,</p>
<p>2 sigma</p></td>
<td rowspan="2">NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
</tr>
<tr class="even">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
</tr>
</tbody>
</table>

Table 4-16. Augmented GPS System Evaluation, Survey, Deformation
Analysis

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 9%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Nationwide</p></td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.0%</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>0.01 meters,</p>
<p>2drms</p></td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
</tr>
<tr class="odd">
<td><p>Predictable Accuracy—</p>
<p>Vertical</p></td>
<td><p>0.001 meters,</p>
<p>2 sigma</p></td>
<td rowspan="2">NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
</tr>
<tr class="even">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
</tr>
</tbody>
</table>

Table 4-17. Augmented GPS System Evaluation, Survey, Mapping

<table style="width:100%;">
<colgroup>
<col style="width: 15%" />
<col style="width: 9%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td>Characteristics</td>
<td>Requirement</td>
<td>USCG</td>
<td>USCG(E)</td>
<td>FM</td>
<td>WAS-1</td>
<td>WAS-2</td>
<td>WAS-3</td>
<td>WAS-4</td>
<td>WAS-5</td>
<td>WAS-6</td>
<td>CORS</td>
<td>Loran-C</td>
</tr>
<tr class="even">
<td><p>Coverage Area—</p>
<p>Nationwide</p></td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>NO</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="odd">
<td>Availability</td>
<td>99.0%</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
<td>YES</td>
</tr>
<tr class="even">
<td><p>Predictable Accuracy—</p>
<p>Horizontal</p></td>
<td><p>0.2 meters,</p>
<p>2drms</p></td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
</tr>
<tr class="odd">
<td><p>Predictable Accuracy—</p>
<p>Vertical</p></td>
<td><p>0.01 meters,</p>
<p>2 sigma</p></td>
<td rowspan="2">NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
<td>NO</td>
</tr>
<tr class="even">
<td colspan="2">Meets Requirements</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>NO</td>
<td>YES</td>
</tr>
</tbody>
</table>

**4.3  Summary of Results**

Tables 4-18 through 4-21 summarize the results of the technical
capabilities evaluation for each mode of operation: aviation, marine,
land, and survey. The table for each mode summarizes the evaluations for
that mode and indicates whether a system meets the requirements for all
phases of that mode of operation. Each entry in Tables 4-18 through 4-21
indicates a \"YES\" if the system meets all the requirements and a
\"NO\" if the system does not meet all the requirements.

Table 4-18. Augmented GPS System Evaluation, Aviation, Summary

  ---------------- ------ --------- ---- ------- ------- ------- ------- ------- ------- ------ ---------
  Phases           USCG   USCG(E)   FM   WAS-1   WAS-2   WAS-3   WAS-4   WAS-5   WAS-6   CORS   Loran-C

  Oceanic En Route NO     NO        NO   YES     YES     YES     YES     NO      NO      NO     NO

  Domestic En      NO     NO        NO   YES     YES     YES     YES     NO      NO      NO     NO
  Route                                                                                         

  Terminal         NO     NO        NO   YES     YES     YES     YES     NO      NO      NO     NO

  Non-precision    NO     NO        NO   YES     YES     YES     YES     NO      NO      NO     NO
  App. and Land                                                                                 

  Category I App.  NO     NO        NO   YES     YES     YES     YES     NO      NO      NO     NO
  and Land                                                                                      

  All Phases       NO     NO        NO   YES     YES     YES     YES     NO      NO      NO     NO
  ---------------- ------ --------- ---- ------- ------- ------- ------- ------- ------- ------ ---------

Table 4-19. Augmented GPS System Evaluation, Marine, Summary

  ---------------- ------ --------- ----- ------- ------- ------- ------- ------- ------- ------ ---------
  Phases           USCG   USCG(E)   FM    WAS-1   WAS-2   WAS-3   WAS-4   WAS-5   WAS-6   CORS   Loran-C

  Harbor/Harbor    YES    YES       NO    NO      NO      NO      NO      NO      YES     NO     YES
  Approach                                                                                       

  Coastal          YES    YES       NO    NO      NO      NO      NO      NO      YES     NO     YES

  Ocean            YES    YES       YES   YES     YES     YES     YES     YES     YES     YES    YES

  All Phases       YES    YES       NO    NO      NO      NO      NO      NO      YES     NO     YES
  ---------------- ------ --------- ----- ------- ------- ------- ------- ------- ------- ------ ---------

Table 4-20. Augmented GPS System Evaluation, Land, Summary

  ---------------- ------ --------- ----- ------- ------- ------- ------- ------- ------- ------ ---------
  Phases           USCG   USCG(E)   FM    WAS-1   WAS-2   WAS-3   WAS-4   WAS-5   WAS-6   CORS   Loran-C

  Highway          NO     YES       YES   YES     NO      YES     YES     YES     YES     NO     YES

  Highway          NO     NO        YES   NO      NO      NO      NO      YES     YES     NO     NO
  (Collision                                                                                     
  Avoid)                                                                                         

  Railroad         NO     NO        NO    NO      NO      NO      NO      NO      NO      NO     NO

  Railroad         NO     YES       YES   YES     NO      YES     YES     YES     NO      NO     YES
  (Control)                                                                                      

  All Phases       NO     NO        NO    NO      NO      NO      NO      NO      NO      NO     NO
  ---------------- ------ --------- ----- ------- ------- ------- ------- ------- ------- ------ ---------

Table 4-21. Augmented GPS System Evaluation, Survey, Summary

  ---------------- ------ --------- ---- ------- ------- ------- ------- ------- ------- ------ ---------
  Phases           USCG   USCG(E)   FM   WAS-1   WAS-2   WAS-3   WAS-4   WAS-5   WAS-6   CORS   Loran-C

  Land Survey      NO     NO        NO   NO      NO      NO      NO      NO      NO      YES    NO

  Hydro Survey     NO     NO        NO   NO      NO      NO      NO      NO      NO      YES    NO

  Deformation      NO     NO        NO   NO      NO      NO      NO      NO      NO      YES    NO
  Survey                                                                                        

  Mapping          NO     NO        NO   NO      NO      NO      NO      NO      NO      YES    NO

  All Phases       NO     NO        NO   NO      NO      NO      NO      NO      NO      YES    NO
  ---------------- ------ --------- ---- ------- ------- ------- ------- ------- ------- ------ ---------

**4.4  Conclusions**

Table 4-22 summarizes the system evaluation for all modes of operation.
It illustrates that no single augmentation system meets the requirements
of all modes of operation. For the land mode, no system evaluated can
meet the collision avoidance requirements of land users because of the
high availability requirements of railroads (100%) or the high accuracy
requirements nationwide (1 meter).

Table 4-22. Augmented GPS System Evaluation, Mode, Summary

  ---------------- ------ --------- ---- ------- ------- ------- ------- ------- ------- ------ ---------
  Mode             USCG   USCG(E)   FM   WAS-1   WAS-2   WAS-3   WAS-4   WAS-5   WAS-6   CORS   Loran-C

  Aviation         NO     NO        NO   YES     YES     YES     YES     NO      NO      NO     NO

  Marine           YES    YES       NO   NO      NO      NO      NO      NO      YES     NO     YES

  Land             NO     NO        NO   NO      NO      NO      NO      NO      NO      NO     NO

  Surveying and    NO     NO        NO   NO      NO      NO      NO      NO      NO      YES    NO
  Other                                                                                         
  ---------------- ------ --------- ---- ------- ------- ------- ------- ------- ------- ------ ---------

**5**

**EVALUATION OF**

**AUGMENTED GPS ARCHITECTURES**

The results of Section 4 indicate that no single proposed system meets
all Federal user requirements. Further, no system evaluated can meet the
collision avoidance requirements of land users because of the high
availability requirements of railroads (100%) or the high accuracy
requirements nationwide (1 meter). All other user requirements can be
met through a combination of systems, referred to as an architecture.
Architectures include systems which individually meet the Federal user
requirements for one or more modes: aviation, marine, land, and/or
survey.

**5.1  Eliminating Systems**

Four systems were not considered for the development of composite
architectures:

> 1\) FM.
>
> 2\) WAS 5.
>
> 3\) WAS 6.
>
> 4\) Loran-C.

The reasons for excluding these systems are explained in the following
paragraphs:

> 1\) FM --- FM subcarrier systems do not provide the integrity,
> availability, and coverage required by aviation and marine users. FM
> subcarriers may not provide coverage for marine and land users in
> rugged or remote areas. FM stations cover approximately 80% of the
> area of North America. Subcarriers broadcast over a smaller area than
> the complete coverage provided by the FM station. Some FM stations in
> remote areas do not operate 24 hours a day, and are the only stations
> available in that area.
>
> 2\) WAS 5 --- Private, GEO satellite-based systems do not meet the
> integrity and availability requirements of aviation.
>
> 3\) WAS 6 --- Because of the premium that the study team attached to
> early realization of the benefits available from augmentation systems,
> LEO satellite-based systems were excluded because of their uncertain
> time frame of availability and a lack of data concerning the systems.

Overall, private systems such as FM, WAS 5, and WAS 6 have not been
designed or developed as navigation aids supporting safety of life
operations. Futher, private system providers are not willing to accept
liability inherent with navigation systems use. If private systems were
to be chosen as part of a navigation architecture, Federal cooperation,
support, and regulation would be necessary to ensure integrity,
availability, and continuity of service.

4\) Loran-C --- A Loran-C system cannot meet aviation integrity and
availability requirements. Additionally, the role of Loran-C in a
satellite-based navigation system is under study at this time. Use of
Loran-C as an additional ranging signal in an integrated navigation
system has been proposed, but to date, no empirical data is available.
Research on the use of Loran-C in a GPS-based system continues.

Combinations of the remaining systems were used to develop composite
architectures.

**5.2  Composite Architectures**

To meet the requirements of the various Federal users, any architecture
will require at least two augmentation systems: one primarily focused on
the requirements of users operating on the earth\'s surface, i.e. land,
marine, and survey users; and one primarily addressing the requirements
of aviation users. It is recognized that some aviation users might
employ the surface/marine local area system, and some land-based users
might employ the wide area aviation system.

While any architecture requires at least two separate systems, there
should be maximum commonality and sharing of resources between all
elements to eliminate duplication of effort and resources. The study
team proposed six potential architectures, each intended to satisfy as
many user requirements as possible:

**Architecture 1**. This architecture, the baseline system, consisted of
the GPS augmentation systems currently planned by USCG and FAA. It
included the 61-site local area differential GPS (LADGPS) system
currently being implemented by USCG for marine use, the FAA's Wide Area
Augmentation System (WAAS) as currently planned to satisfy aviation
requirements for en route through Category I precision approach, and
FAA\'s LADGPS systems to satisfy Category II/III precision approach
requirements. All of the reference stations included in this
architecture would be compliant with the Continuously Operating
Reference Station (CORS) standard. Such stations would have the
capability of storing a standardized set of data to support the widest
possible number of post-processing applications. Although Architecture 1
did not satisfy many land transportation and survey requirements, it was
included to provide a benchmark against which the remaining five, more
viable, alternatives could be compared.

**Architecture 2**.  This architecture consisted of an expanded version
of USCG\'s LADGPS system to provide nationwide coverage for marine
[and]{.underline} land users. It also included FAA's WAAS as currently
planned to satisfy aviation requirements for en route through Category I
precision approach, and FAA\'s LADGPS systems to satisfy Category II/III
precision approach requirements. All of the reference stations included
in this architecture would comply with the CORS standard.

**Architecture 3**.  This architecture consisted of an expanded version
of USCG\'s LADGPS system to provide nationwide coverage for marine and
land users and a variant of FAA's WAAS to satisfy aviation requirements
for en route through nonprecision approach only. Category I, II, and III
precision approach requirements would be satisfied by FAA\'s LADGPS
systems. All of the reference stations included in this architecture
would comply with the CORS standard.

**Architecture 4**.  This architecture included an expanded version of
USCG\'s LADGPS system to provide nationwide coverage for marine and land
users. It also included a modified version of FAA's WAAS, which provided
corrections at other than the GPS L1 frequency, to satisfy aviation
requirements for en route through Category I precision approach.
Category II/III precision approach requirements would be satisfied by
FAA\'s LADGPS systems. All of the reference stations included in this
architecture would comply with the CORS standard.

**Architecture 5**.  This architecture included an expanded version of
USCG\'s LADGPS system to provide nationwide coverage for marine and land
users. It also included a modified version of the FAA's WAAS which would
encrypt all of the corrections for increased security. The modified WAAS
would satisfy aviation requirements for en route through Category I
precision approach. Category II/III precision approach requirements
would be satisfied by FAA\'s LADGPS systems. All of the reference
stations included in this architecture would comply with the CORS
standard.

**Architecture 6**.  This architecture included an expanded version of
USCG\'s LADGPS system to provide nationwide coverage for marine and land
users and to satisfy aviation accuracy requirements for Category I
precision approach. It also included a variant of the FAA\'s WAAS to
satisfy aviation requirements for en route through nonprecision
approach. Category II/III precision approach requirements would be
satisfied by FAA\'s LADGPS systems. All of the reference stations
included in this architecture would comply with the CORS standard.

Architecture 6 was evaluated extensively as it appeared capable of
meeting stated requirements at a lower cost than the other five
architectures. In the course of the evaluation, it was found that
possible interference of signal reception could occur to aircraft which
were flying through conditions conducive to the creation of
precipitation static (P-Static). While an extensive study had not been
performed of this phenomenon, it raised significant concerns about
signal availability. Consequently, Architecture 6 was not considered in
the second stage of the decision matrix.

**5.3  Architecture Evaluation**

Each of the five remaining architectures were evaluated using the second
stage of the decision matrix, which constituted a modified version of a
classic multi-attribute utility analysis. The development of the
decision matrix is described in detail in Appendix J. The second stage
of the matrix consisted of a model with three major parameters:
Performance, Cost, and Security. These parameters were broken down into
several different factors, and each architecture was scored for each
factor. A brief description of each of the factors and their scoring is
provided below.

> **Performance Factors:**
>
> • Real Time Accuracy --- This score reflects how well an architecture
> meets the real time accuracy requirements.
>
> • Integrity (Time to Alarm) --- The time to alarm score reflects how
> well a system provides timely warnings to users when the system or
> parts of the system should not be used.
>
> • Availability --- The availability score reflects architecture
> performance, without failure, over a one-year period. Availability is
> the probability that service, meeting the coverage constraints, will
> be available to the user.
>
> • Time Frame of Availability --- The score for time frame of
> availability reflects the ability of a system to meet an initial
> operating capability between 1996 and 1998.
>
> • Coverage --- The coverage score reflects the architecture\'s ability
> to provide service in a geographic area.
>
> • International Compatibility --- This score reflects how compatible
> and acceptable this architecture is to the international community. It
> includes compatibility with international standards and agreements, as
> well as ease of use in a seamless worldwide infrastructure.
>
> **Cost Factors (estimated in FY 94 dollars):**
>
> • Infrastructure Cost --- This cost score reflects the cost of initial
> implementation and the 20 year life cycle cost for the architecture.
>
> • User Equipment Cost --- This score reflects the cost of equipment to
> the user.

**Security Factors:**

> • Access Control --- This score reflects the capability to selectively
> deny unauthorized use through command and control features of the
> architecture.
>
> • Level of Influence --- This score reflects the level of political
> influence and managerial control the U.S. has over denying use of the
> architecture.
>
> • Interdiction --- The interdiction score reflects the U.S. and allied
> military forces\' ability to deny any adversary\'s military use of an
> architecture\'s enhanced performance, through a nonelectronic physical
> means, within a theater of operations.
>
> • Post-Decision Response Time --- The post-decision response time
> score reflects the time required to implement denial once the decision
> to deny access to the architecture has been made.
>
> • Jammability --- The jammability score reflects the ability of U.S.
> and Allied forces to electronically deny an adversary\'s use of an
> architecture.
>
> • Vulnerability of Denial --- The vulnerability of denial score
> reflects an assessment of how easily the access control features of
> the architecture can be circumvented by unauthorized users.

Weights were assigned to each factor in the matrix as an indication of
that factor\'s relative importance to the overall goals of this study.
The weights for evaluation factors were developed in an iterative
process by the study team and the Working Group.

The scores for the evaluation factor were multiplied by the weight
assigned to the factor to obtain a weighted score. Overall Performance,
Cost, and Security scores for each architecture were obtained by summing
the weighted score column.

Scores, weights, weighted scores, and total scores for the various
architectures are shown in Tables 5-1 through 5-3. Detailed explanations
for the scores assigned to each architecture are contained in Appendix
K.

Table 5-1. Weighted Analytical Decision Matrix --- Performance

<table>
<colgroup>
<col style="width: 24%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td colspan="2"></td>
<td colspan="10"><strong>ARCHITECTURES</strong></td>
</tr>
<tr class="even">
<td colspan="2"></td>
<td colspan="2">1</td>
<td colspan="2">2</td>
<td colspan="2">3</td>
<td colspan="2">4</td>
<td colspan="2">5</td>
</tr>
<tr class="odd">
<td colspan="2"></td>
<td colspan="2">USCG+WAS-1</td>
<td colspan="2">USCG(E)+WAS-1</td>
<td colspan="2">USCG(E)+WAS-2</td>
<td colspan="2">USCG(E)+WAS-3</td>
<td colspan="2">USCG(E)+WAS-4</td>
</tr>
<tr class="even">
<td><strong>Evaluation Parameters</strong></td>
<td rowspan="2">Weight</td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
</tr>
<tr class="odd">
<td><strong>PERFORMANCE</strong></td>
</tr>
<tr class="even">
<td>Real Time Accuracy</td>
<td>23.5</td>
<td>80</td>
<td>1880</td>
<td>80</td>
<td>1880</td>
<td>80</td>
<td>1880</td>
<td>80</td>
<td>1880</td>
<td>80</td>
<td>1880</td>
</tr>
<tr class="odd">
<td>Integrity (Time to Alarm)</td>
<td>21.5</td>
<td>100</td>
<td>2150</td>
<td>100</td>
<td>2150</td>
<td>100</td>
<td>2150</td>
<td>100</td>
<td>2150</td>
<td>100</td>
<td>2150</td>
</tr>
<tr class="even">
<td>Availability</td>
<td>19.5</td>
<td>90</td>
<td>1755</td>
<td>90</td>
<td>1755</td>
<td>90</td>
<td>1755</td>
<td>90</td>
<td>1755</td>
<td>90</td>
<td>1755</td>
</tr>
<tr class="odd">
<td>Time Frame of Availability (IOC)</td>
<td>15.5</td>
<td>95</td>
<td>1472.5</td>
<td>90</td>
<td>1395</td>
<td>90</td>
<td>1395</td>
<td>0</td>
<td>0</td>
<td>0</td>
<td>0</td>
</tr>
<tr class="even">
<td>Coverage</td>
<td>14.5</td>
<td>0</td>
<td>0</td>
<td>90</td>
<td>1305</td>
<td>90</td>
<td>1305</td>
<td>90</td>
<td>1305</td>
<td>90</td>
<td>1305</td>
</tr>
<tr class="odd">
<td>International Compatibility</td>
<td>5.5</td>
<td>95</td>
<td>522.5</td>
<td>95</td>
<td>522.5</td>
<td>85</td>
<td>467.5</td>
<td>88</td>
<td>484</td>
<td>30</td>
<td>165</td>
</tr>
<tr class="even">
<td><strong>Total Performance Score</strong></td>
<td></td>
<td></td>
<td>7780</td>
<td></td>
<td>9007.5</td>
<td></td>
<td>8952.5</td>
<td></td>
<td>7574</td>
<td></td>
<td>7255</td>
</tr>
</tbody>
</table>

Table 5-2. Weighted Analytical Decision Matrix --- Cost

<table>
<colgroup>
<col style="width: 24%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td colspan="2"></td>
<td colspan="10"><strong>ARCHITECTURES</strong></td>
</tr>
<tr class="even">
<td colspan="2"></td>
<td colspan="2">1</td>
<td colspan="2">2</td>
<td colspan="2">3</td>
<td colspan="2">4</td>
<td colspan="2">5</td>
</tr>
<tr class="odd">
<td colspan="2"></td>
<td colspan="2">USCG+WAS-1</td>
<td colspan="2">USCG(E)+WAS-1</td>
<td colspan="2">USCG(E)+WAS-2</td>
<td colspan="2">USCG(E)+WAS-3</td>
<td colspan="2">USCG(E)+WAS-4</td>
</tr>
<tr class="even">
<td><strong>Evaluation Parameters</strong></td>
<td rowspan="2">Weight</td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
</tr>
<tr class="odd">
<td><strong>COST</strong></td>
</tr>
<tr class="even">
<td>Infrastructure Cost</td>
<td>50</td>
<td>20</td>
<td>1000</td>
<td>17</td>
<td>850</td>
<td>12</td>
<td>600</td>
<td>17</td>
<td>850</td>
<td>0</td>
<td>0</td>
</tr>
<tr class="odd">
<td>User Equipment Cost</td>
<td>50</td>
<td>14</td>
<td>700</td>
<td>14</td>
<td>700</td>
<td>9</td>
<td>450</td>
<td>9</td>
<td>450</td>
<td>0</td>
<td>0</td>
</tr>
<tr class="even">
<td><strong>Total Cost Score</strong></td>
<td></td>
<td></td>
<td>1700</td>
<td></td>
<td>1550</td>
<td></td>
<td>1050</td>
<td></td>
<td>1300</td>
<td></td>
<td>0</td>
</tr>
</tbody>
</table>

Table 5-3. Weighted Analytical Decision Matrix --- Security

<table>
<colgroup>
<col style="width: 24%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
<col style="width: 6%" />
</colgroup>
<tbody>
<tr class="odd">
<td colspan="2"></td>
<td colspan="10"><strong>ARCHITECTURES</strong></td>
</tr>
<tr class="even">
<td colspan="2"></td>
<td colspan="2">1</td>
<td colspan="2">2</td>
<td colspan="2">3</td>
<td colspan="2">4</td>
<td colspan="2">5</td>
</tr>
<tr class="odd">
<td colspan="2"></td>
<td colspan="2">USCG+WAS-1</td>
<td colspan="2">USCG(E)+WAS-1</td>
<td colspan="2">USCG(E)+WAS-2</td>
<td colspan="2">USCG(E)+WAS-3</td>
<td colspan="2">USCG(E)+WAS-4</td>
</tr>
<tr class="even">
<td><strong>Evaluation Parameters</strong></td>
<td rowspan="2">Weight</td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
<td rowspan="2">Score</td>
<td rowspan="2"><p>Weighted</p>
<p>Score</p></td>
</tr>
<tr class="odd">
<td><strong>SECURITY</strong></td>
</tr>
<tr class="even">
<td>Access Control</td>
<td>37</td>
<td>0</td>
<td>0</td>
<td>0</td>
<td>0</td>
<td>50</td>
<td>1850</td>
<td>0</td>
<td>0</td>
<td>75</td>
<td>2775</td>
</tr>
<tr class="odd">
<td>Level of Influence</td>
<td>19</td>
<td>80</td>
<td>1520</td>
<td>80</td>
<td>1520</td>
<td>80</td>
<td>1520</td>
<td>80</td>
<td>1520</td>
<td>90</td>
<td>1710</td>
</tr>
<tr class="even">
<td>Interdiction</td>
<td>14</td>
<td>0</td>
<td>0</td>
<td>0</td>
<td>0</td>
<td>100</td>
<td>1400</td>
<td>0</td>
<td>0</td>
<td>100</td>
<td>1400</td>
</tr>
<tr class="odd">
<td>Post-decision Response Time</td>
<td>13</td>
<td>80</td>
<td>1040</td>
<td>80</td>
<td>1040</td>
<td>80</td>
<td>1040</td>
<td>80</td>
<td>1040</td>
<td>80</td>
<td>1040</td>
</tr>
<tr class="even">
<td>Jammability</td>
<td>11</td>
<td>5</td>
<td>55</td>
<td>5</td>
<td>55</td>
<td>100</td>
<td>1100</td>
<td>30</td>
<td>330</td>
<td>100</td>
<td>1100</td>
</tr>
<tr class="odd">
<td>Vulnerability of Denial</td>
<td>6</td>
<td>50</td>
<td>300</td>
<td>50</td>
<td>300</td>
<td>50</td>
<td>300</td>
<td>50</td>
<td>300</td>
<td>50</td>
<td>300</td>
</tr>
<tr class="even">
<td><strong>Total Security Score</strong></td>
<td></td>
<td></td>
<td>2915</td>
<td></td>
<td>2915</td>
<td></td>
<td>7210</td>
<td></td>
<td>3190</td>
<td></td>
<td>8325</td>
</tr>
</tbody>
</table>

The five architectures are compared on the basis of performance vs.
cost, performance vs. security, and security vs. cost in Figures 5-1
through 5-3. The upper right quandrant of each chart represents the
location for the most desirable architectures. The numbers that label
the data points on the charts correspond to the architectures referred
to in Tables 5-1 through 5-3. The figures indicate that Architecture 2
provides the best performance vs. cost, Architecture 3 provides the best
performance vs. security, and Architecture 3 provides an intermediate
level of security at an intermediate cost.

![](media/image11.wmf){width="6.221527777777778in"
height="3.7222222222222223in"}![](media/image12.wmf){width="6.270138888888889in"
height="3.7729166666666667in"}

![](media/image13.wmf){width="6.223611111111111in"
height="3.7222222222222223in"}

**5.4  Summary of Results**

**Architecture 1, USCG/WAS 1/CORS** --- This architecture is included as
a baseline architecture for comparative purposes. This is the default
architecture which would be in place if no actions are taken. It does
not meet the minimum requirements for Federal users and cannot serve as
the Federal augmentation system. This architecture ranked third in
overall performance because its does not meet the minimum requirements
for coverage. As the least expensive architecture, it ranked first for
cost. It ranked last for security because of the wide area broadcast of
differential corrections on the L1 frequency.

**Architecture 2, USCG(E)/WAS 1/CORS** --- This architecture ranked
first in performance because it had the earliest IOC and scored highest
for international compatibility. It ranked second for cost since the
increase in cost for the expansion of the USCG system is minor when
compared to the cost of the accuracy component of the WAAS. It ranked
last for security because of the wide area broadcast of differential
corrections on the L1 frequency.

**Architecture 3, USCG(E)/WAS 2/CORS** --- This architecture ranked
second in performance because it had a later IOC and a lower
international compatibility score than Architecture 2. It ranked fourth
for cost because it required an additional 620 LADGPS systems for
Category I precision approach requirements. It ranked second for
security because it does not provide wide area broadcast of differential
corrections.

**Architecture 4, USCG(E)/WAS 3/CORS** --- This architecture ranked
fourth in performance because it had a later IOC date and a lower
international compatibility score than other architectures. It ranked
third for cost because of the relocation of the WAAS downlink to a
frequency other than L1, resulting in higher infrastructure and user
equipment costs. It ranked third for security because of the wide area
broadcast of differential corrections.

**Architecture 5, USCG(E)/WAS 4/CORS** --- This architecture ranked
fifth in performance because of the late IOC date and low international
compatibility score. It ranked fifth for cost because of the addition of
encrypted WAAS data links. It ranked first for security because of the
addition of encrypted WAAS data links.

**6**

**RECOMMENDATIONS**

This section presents the study conclusions and recommendations based
upon the requirements of users, available technologies, and the
evaluation contained in this report. The recommendations are subdivided
into two categories, architecture recommendations and architecture
independent recommendations.

**6.1  Recommended Architecture**

There are two candidates that could be selected as the National
augmentation architecture. The selection of one of these two viable
alternatives is dependent on overall U.S. Government policy regarding
augmentation systems.

> • If security concerns are not the overriding consideration and do not
> predominate over other benefits available from an augmented GPS,
> composite Architecture 2 is the recommended National augmentation
> system.
>
> • If, however, security concerns are of such significance as to
> predominate over economic and other benefits available from an
> augmented GPS, then Architecture 3 is the recommended National
> augmentation system.

Either of these architectures will meet aviation user requirements for
all phases of flight, marine user requirements for all modes of
operation, and most land user requirements including IVHS, railroad, and
survey. However, neither architecture will satisfy highway collision
avoidance because of the high degree of accuracy (1 meter) required
nationwide. Neither architecture will provide the 100% availability
required for railroad collision avoidance. These applications may
require the development or use of other technologies either in
conjunction with GPS or independent of GPS.

**6.2  Architecture Independent Recommendations**

Based on its research and evaluation, the study team also recommends the
following:

> • FAA should continue to implement its WAAS and LADGPS systems as
> currently planned.

• DOT, in coordination and cooperation with DOC, should plan, install,
operate, and maintain an expanded low frequency/medium frequency beacon
system modeled after USCG\'s LADGPS system to provide nationwide
coverage for land and marine users. Prior to implementing this system, a
study should be performed to determine the number and optimum location
of beacons necessary for nationwide coverage.

• All Federally-provided reference stations should comply with the CORS
standard.

• DOT should continue to evaluate system risks and appropriate measures
needed to ensure safe and reliable augmentation services. Further, DOT,
with the assistance of DOD, should test and evaluate measures to
mitigate the susceptibility of Federally-provided augmentation systems
to all forms of interference, including jamming and spoofing.

• DOT, in conjunction with other Federal agencies, should coordinate the
implementation, operation, and maintenance of all Federally-operated
augmented GPS systems to ensure optimal use of resources by maximizing
commonality of system components.

• Different formats for augmentation data have been developed to meet
the requirements of particular user communities and to make optimum use
of data links planned for augmenting GPS. For the architectures
considered, there is no compelling technical or economic reason for
developing a single, standardized data format for use by all
Federally-operated augmentation systems. Consequently, no effort should
be expended on the conversion of existing broadcast formats to a common
data format in the near term. Use of the Receiver Independent Exchange
(RINEX) format is recommended for post-processing applications. In
addition, an international standards working group should be identified
to address any future data format issues.

• A central repository for GPS augmentation information should be
maintained. This information should be made available to the public via
the existing USCG Navigation Information Service.

• A further study should be undertaken to investigate spectrum
allocation and bandwidth requirements for any future,
Federally-provided, differential GPS system.

**7**

**REFERENCES**

\[1\] Joint U.S. Department of Defense/U.S. Department of Transportation
Task Force, *The Global Positioning System: Management and Operation of
a Dual Use System*, Washington, DC, December 1993.

\[2\] U.S. Department of Defense/U.S. Department of Transportation,
*1992 Federal Radionavigation Plan*, Washington, DC, January 1993.

\[3\] U.S. Department of Defense/U.S. Department of Transportation,
*DRAFT 1994 Federal Radionavigation Plan*, Washington, DC, August 1994.

\[4\] U.S. Department of Transportation/IVHS AMERICA, *DRAFT National
Program Plan for Intelligent Vehicle-Highway Systems*, Washington, DC,
May 1994.

\[5\] W.C. Collier and R.J. Weiland, \"Smart cars, smart highways,\"
*IEEE Spectrum*, April 1994.

\[6\] Radio Technical Commission for Maritime Services (RTCM) Special
Committee No. 104, *RTCM Recommended Standards for Differential Navstar
GPS Service, Version 2.1*, Washington, DC, January 1994.

\[7\] KV Research Inc., *Differential GPS Markets in the 1990\'s: A
North American Cross-Industry Study*, Cincinnati, OH, September 1992.

\[8\] Federal Aviation Administration, *Wide Area Augmentation System
Specification, FAA-E-2892*, Washington, DC, May 1994.

\[9\] RTCA Inc., *Minimum Operation Performance Standards for Sensors
Using Global Positioning System/Wide Area Augmentation System, Draft 1*,
Washington, DC, July 1994.

\[10\] J.V. Carroll, \"Availability Performance Comparisons of Combined
Loran-C/GPS and Standalone GPS Approach Navigation Systems,\" in *Proc.
IEEE 1994 Position Location and Navigation Symposium (PLANS)*, Las
Vegas, NV, April 1994, pp.77-83.

**APPENDIX A**

**ACRONYMS AND ABBREVIATIONS**

The following is a listing of acronyms and abbreviations pertinent to
the subject of radionavigation in general and the Global Positioning
System in particular:

AGPS Augmented Global Positioning System

A‑S Anti‑Spoofing

ASD/C3I Assistant Secretary of Defense for Command, Control,
Communications and Intelligence

ASR Airport Surveillance Radar

ATC Air Traffic Control

ATCS Advanced Train Control Systems

ATCRBS Air Traffic Control Radar Beacon System

ATIS Advanced Traveler Information System

ATS Air Traffic Service

ATMS Advanced Traffic Management System

AVCS Advanced Vehicle Control System

AVI Automatic Vehicle Identification

AVL Automatic Vehicle Location

AVM Automatic Vehicle Monitoring

CAT category

C/A Code Course/Acquisition Code (GPS)

CCZ Coastal Confluence Zone

CEP Circular Error Probable

CGS Civil GPS Service

CGSIC Civil GPS Service Interface Committee

CONUS Continental United States

CORS Continuously Operating Reference Station

CVO Commercial Vehicle Operations

DGPS Differential Global Positioning System

DH Decision Height

DME Distance Measuring Equipment

DME/P Precision Distance Measuring Equipment

DMSP Defense Meteorological Satellite Program

DOC Department of Commerce

DOD Department of Defense

DOI Department of the Interior

DOP Dilution of Precision

DOT Department of Transportation

DR Dead Reckoning

drms Distance Root Mean Squared

ECEF Earth Centered Earth Fixed

EMC Electromagnetic Compatibility

EMI Electromagnetic Interference

FAA Federal Aviation Administration

FAF Final Approach Fix

FCC Federal Communications Commission

FEMA Federal Emergency Management Agency

FHWA Federal Highway Administration

FL Flight Level

FM Frequency Modulation

FMS Flight Management System

FOC Full Operational Capability

FRA Federal Railroad Administration

FRP Federal Radionavigation Plan

FTE Flight Technical Error

GA General Aviation

GDOP Geometric Dilution of Precision

GHz Gigahertz

GLONASS Global Orbiting Navigation Satellite System

GNSS Global Navigation Satellite System

GOES Geosynchronous Operational Environmental Satellite

GPS Global Positioning System

HDOP Horizontal Dilution of Precision

HF High Frequency

HHA Harbor/Harbor Approach

Hz Hertz (cycles per second)

IALA International Association of Lighthouse Authorities

ICAO International Civil Aviation Organization

IFR Instrument Flight Rules

ILS Instrument Landing System

IMO International Maritime Organization

INMARSAT International Maritime Satellite Organization

INS Inertial Navigation System

IOC Initial Operational Capability

ITS Intelligent Transportation System

ITU International Telecommunication Union

IVHS Intelligent Vehicle Highway Systems

JPO Joint Program Office

kHz Kilohertz

km Kilometer

LADGPS Local Area Differential GPS

LEO Low Earth Orbiting

LF Low Frequency

Loran-C Long‑Range Navigation, Version C

MCS GPS Master Control Station

MARAD Maritime Administration

MF Medium Frequency

MHz Megahertz

MLS Microwave Landing System

mm Millimeter

MOA Memorandum of Agreement

MOPS Minimum Operational Performance Standard

MSK Minimum Shift Keying

MTBF Mean Time Between Failures

NAD North American Datum

NAS National Airspace System

NASA National Aeronautics and Space Administration

NCA National Command Authority

NDB Non directional Beacon

NGS National Geodetic Survey

NHTSA National Highway Traffic Safety Administration

nm Nautical Mile

NOAA National Oceanic and Atmospheric Administration

NOS National Ocean Service

NOTAM Notice to Airmen

ns Nanosecond

NSF National Science Foundation

NTIA National Telecommunications and Information Administration

NWS National Weather Service

O&M Operation & Maintenance

OCS Operational Control Segment

OMB Office of Management and Budget

OSD Office of the Secretary of Defense

OTP Office of Telecommunications Policy

P‑code Pseudorandom Tracking Code

PDOP Position Dilution of Precision

POS/NAV Positioning and Navigation

PPS Precise Positioning Service

PRC Pseudorange Correction

PRN Pseudo Random Noise

PTC Positive Train Control

PTS Positive Train Separation

RAIM Receiver Autonomous Integrity Monitoring

R&D Research & Development

RF Radio Frequency

RFI Radio Frequency Interference

RINEX Receiver Independent Exchange

RNP Required Navigation Performance

RRC Range‑Rate Corrections

RSPA Research and Special Programs Administration

RTCM Radio Technical Commission for Maritime Services

SA Selective Availability

SAR Search and Rescue

SEP Spherical Error Probable

SIS Signal in space

SLSDC Saint Lawrence Seaway Development Corporation

SPS Standard Positioning Service

SV Space Vehicle

TMC Traffic Management Center

TOC Traffic Operations Center

TVA Tennessee Valley Authority

UHF Ultra High Frequency

URE User Range Error

USAF United States Air Force

USCG United States Coast Guard

USDA United States Department of Agriculture

USGS United States Geological Survey

USNO United States Naval Observatory

UTC Coordinated Universal Time

VFR Visual Flight Rules

VHF Very High Frequency

VLF Very Low Frequency

VOR Very High Frequency Omnidirectional Range

VSAT Very‑Small Aperture Terminals

VTS Vessel Traffic Services

WAAS Wide Area Augmentation System

WADGPS Wide Area Differential GPS

WAS Wide Area System

WDGPS Wide Area Differential GPS

WGS World Geodetic System

WRC World Radio Conference

**APPENDIX B**

**DEFINITIONS**

**Accuracy** --- The degree of conformance between the estimated or
measured position and/or velocity of a platform at a given time and its
true position or velocity. Radionavigation system accuracy is usually
presented as a statistical measure of system error and is specified as:

> Predictable --- The accuracy of a radionavigation system\'s position
> solution with respect to the charted solution. Both the position
> solution and the chart must be based upon the same geodetic datum.
>
> Repeatable --- The accuracy with which a user can return to a position
> whose coordinates have been measured at a previous time with the same
> navigation system.
>
> Relative --- The accuracy with which a user can measure position
> relative to that of another user of the same navigation system at the
> same time.

**Air Traffic Control (ATC)** --- A service operated by appropriate
authority to promote the safe, orderly, and expeditious flow of air
traffic.

**Approach Reference Datum** --- A point at a specified height above the
runway centerline and the threshold. The height of the MLS approach
reference datum is 15 meters (50 ft). A tolerance of plus 3 meters (10
ft) is permitted.

**Area Navigation (RNAV)** --- A method of navigation that permits
aircraft operations on any desired course within the coverage of
station‑referenced navigation signals or within the limits of
self‑contained system capability.

**Automatic Dependent Surveillance** --- A function in which aircraft
automatically transmit navigation data derived from onboard navigation
systems via a datalink for use by air traffic control.

**Availability** --- The availability of a navigation system is the
percentage of time that the services of the system are usable.
Availability is an indication of the ability of the system to provide
usable service within the specified coverage area. Signal availability
is the percentage of time that navigational signals transmitted from
external sources are available for use. Availability is a function of
both the physical characteristics of the environment and the technical
capabilities of the transmitter facilities.

It is important to realize that the term \"availability\" has different
meanings for different systems. For example, the U.S. Coast Guard
defines availability as the percentage of time in a one month period
during which a DGPS Broadcast transmits healthy PRC\'s at its specified
output level (e.g., exceeding 75 uV/m for 100 bps broadcast). The
specification indicates HDOP \< 2.3 is assumed. This definition is also
called \"broadcast availability\" while other sub-definitions include
\"signal availability\" and \"user availability.\" Broadcast and signal
availabilities primarily refer to healthy PRC\'s at the specified output
level while user availability takes into account environmental effects
such as noise.

The FAA has a much broader definition of availability which is applied
to the WAAS. Availability is defined as the probability that the
navigation and fault detection functions are operational and that the
GPS/WAAS signal in space accuracy, integrity, and continuity of function
requirements are met.

For the purposes of this report, the FAA definition of availability
applies to aviation requirements and systems designed to meet aviation
requirements while the concept of broadcast availability applies to the
USCG and other systems. In some cases, the estimated availability may be
relative to a year instead of a month.

**Block II/IIA** --- The satellites that will form the GPS constellation
at FOC.

**Circular Error Probable (CEP)** --- In a circular normal distribution
(the magnitudes of the two one‑dimensional input errors are equal and
the angle of cut is 90°), circular error probable is the radius of the
circle containing 50% of the individual measurements being made, or the
radius of the circle inside of which there is a 50% probability of being
located.

**Coastal Confluence Zone (CCZ)** --- Harbor entrance to 93 km (50
nautical miles) offshore or the edge of the continental shelf (100
fathom curve), whichever is greater.

**Common-use Systems** --- Systems used by both civil and military
sectors.

**Conterminous U.S.** --- Forty‑eight adjoining states and the District
of Columbia.

**Coordinated Universal Time (UTC)** --- UTC, an atomic time scale, is
the basis for civil time. It is occasionally adjusted by one‑second
increments to ensure that the difference between the uniform time scale,
defined by atomic clocks, does not differ from the earth\'s rotation by
more than 0.9 seconds.

**Coverage** --- The coverage provided by a radionavigation system is
that surface area or space volume in which the signals are adequate to
permit the user to determine position to a specified level of accuracy.
Coverage is influenced by system geometry, signal power levels, receiver
sensitivity, atmospheric noise conditions, and other factors which
affect signal availability.

**Differential** --- A technique used to improve radionavigation system
accuracy by determining positioning error at a known location and
subsequently transmitting the determined error, or corrective factors,
to users of the same radionavigation system, operating in the same area.

**Distance Root Mean Square (drms)** --- The root‑mean‑square value of
the distances from the true location point of the position fixes in a
collection of measurements. As used in this document, 2 drms is the
radius of a circle that contains at least 95% of all possible fixes that
can be obtained with a system at any one place. Actually, the percentage
of fixes contained within 2 drms varies between approximately 95.5% and
98.2%, depending on the degree of ellipticity of the error distribution.

**En Route** --- A phase of navigation covering operations between a
point of departure and termination of a mission. For airborne missions,
the en route phase of navigation has two subcategories, en route
domestic and en route oceanic.

**En Route Domestic** --- The phase of flight between departure and
arrival terminal phases, with departure and arrival points within the
conterminous United States.

**En Route Oceanic** --- The phase of flight between the departure and
arrival terminal phases, with an extended flight path over an ocean.

**Flight Technical Error (FTE)** --- The contribution of the pilot in
using the presented information to control aircraft position.

**Full Operational Capability (FOC)** --- For GPS, this is defined as
the capability that will occur when 24 operational (Block II/IIA)
satellites are operating in their assigned orbits and have been tested
for military functionality and meet military requirements.

**Geocentric** --- Relative to the earth as a center, measured from the
center of mass of the earth.

**Geodesy** --- The science related to the determination of the size and
shape of the Earth (geoid) by such direct measurements as triangulation,
leveling, and gravimetric observations; which determines the external
gravitational field of the Earth and, to a limited degree, the internal
structure.

**Geometric Dilution Of Precision (GDOP)** --- All geometric factors
that degrade the accuracy of position fixes derived from
externally‑referenced navigation systems.

**Inclination** --- One of the orbital elements (parameters) that
specifies the orientation of an orbit. Inclination is the angle between
the orbital plane and a reference plane, the plane of the celestial
equator for geocentric orbits and the ecliptic for heliocentric orbits.

**Initial Operational Capability (IOC)** --- For GPS, this is defined as
the capability that occurred when 24 GPS satellites (Block I/II/IIA)
were first operating in their assigned orbits and were available for
navigation use (December 1993).

**Integrity** --- Integrity is the ability of a system to provide timely
warnings to users when the system should not be used for navigation.

**Meaconing** --- A technique of manipulating radio frequency signals to
provide false navigation information.

**Mode S** --- An enhanced mode of secondary surveillance radar (SSR)
that permits the two‑way exchange of digital data between ground
facilities and aircraft. Ground‑to‑air Mode S signals are transmitted on
the 1030 MHz interrogation frequency channel. Air‑to‑ground Mode S
signals are transmitted on the 1090 MHz reply frequency channel.

**Nanosecond (ns)** --- One billionth of a second.

**National Airspace System (NAS)** --- The NAS includes U.S. airspace;
air navigation facilities, equipment and services; airports or landing
areas; aeronautical charts, information and service; rules, regulations
and procedures; technical information; and labor and material used to
control and/or manage flight activities in airspace under U.S.
jurisdiction. System components shared with the military are included.

**National Command Authority (NCA)** --- The NCA is the President, or
the Secretary of Defense with the approval of the President. The term
NCA is used to signify constitutional authority to direct the Armed
Forces in their execution of military action. Both movement of troops
and execution of military action must be directed by the NCA; by law, no
one else in the chain of command has the authority to take such action.

**Nautical Mile (nm)** --- A unit of distance used principally in
navigation. The International Nautical Mile is 1,852 meters long.

**Navigation** --- The process of planning, recording, and controlling
the movement of a craft or vehicle from one place to another.

**Nonprecision Approach** --- A standard instrument approach procedure
in which no electronic glide slope is provided (e.g., VOR, TACAN,
Loran‑C, or NDB).

**Precise Time** --- A time requirement accurate to within 10
milliseconds.

**Precision Approach** --- A standard instrument approach procedure in
which an electronic glide scope is provided; e.g., the Instrument
Landing System (ILS).

> ILS Category I (CAT I) --- An ILS approach procedure that provides for
> approach to a height above touchdown of not less than 200 feet and
> with runway visual range of not less than 1,800 feet.
>
> ILS Category II (CAT II) --- An ILS approach procedure that provides
> for approach to a height above touchdown of not less than 100 feet and
> a runway visual range of not less than 1,200 feet.

ILS Category III (CAT III) ---

> IIIA --- An ILS approach procedure that provides for approach without
> a decision height minimum and with runway visual range of not less
> than 700 feet.
>
> IIIB --- An ILS approach procedure that provides for approach without
> a decision height minimum and with runway visual range of not less
> than 150 feet.
>
> IIIC --- An ILS approach procedure that provides for approach without
> a decision height minimum and without runway visual range minimum.

GPS Special Category I --- A special issuance instrument approach
procedure with minima not lower than 200 feet height above touchdown
zone or runway visual range of not less than 1,800 feet. Special
instrument approach procedures are approved by the FAA for individual
operators, but are not published in Federal aviation regulations for
public use.

**Radiodetermination** --- The determination of position, or the
obtaining of information relating to positions, by means of the
propagation properties of radio waves.

**Radiolocation** --- Radiodetermination used for purposes other than
those of radionavigation.

**Radionavigation** --- The determination of position, or the obtaining
of information relating to position, for the purposes of navigation by
means of the propagation properties of radio waves.

**Reliability** --- The probability of performing a specified function
without failure under given conditions for a specified period of time.

**Required Navigation Performance** --- A statement of the navigation
performance accuracy necessary for operation within a defined airspace,
including the operating parameters of the navigation systems used within
that airspace.

**RHO (Ranging Mode)** --- A mode of operation of a radionavigation
system in which the times for the radio signals to travel from each
transmitting station to the receiver are measured rather than their
differences (as in the hyperbolic mode).

**RINEX** **(Receiver-Independent Exchange)** --- RINEX is a data format
based upon a set of standard definitions for GPS observables (time,
phase, range). Use of RINEX allows appropriate software to process RINEX
formatted GPS data, even though it is collected using different vendor
receivers. Most GPS manufacturers use their own proprietary formats for
the data collected using their equipment. Before the advent of RINEX,
users had no way to post-process GPS data collected using different
vendor equipment, unless they had access to the restricted knowledge
about the manufacturer\'s proprietary format. RINEX removes this
restriction on the user community by providing a standard format which
can be used for the post-processing and analysis of GPS data.

**Roadside Beacons** --- A system using infrared or radio waves to
communicate between transceivers placed at roadsides and the in‑vehicle
transceivers for navigation and route guidance functions.

**Sigma** --- See Standard Deviation.

**Spherical Error Probable (SEP)** --- The radius of a sphere within
which there is a 50 percent probability of locating a point or being
located. SEP is the three‑dimensional analogue of CEP.

**Standard Deviation (sigma)** --- A measure of the dispersion of random
errors about the mean value. If a large number of measurements or
observations of the same quantity are made, the standard deviation is
the square root of the sum of the squares of deviations from the mean
value divided by the number of observations less one.

**Supplemental Air Navigation System** --- An approved navigation system
that can be used in controlled airspace of the National Airspace System
in conjunction with a primary means of navigation.

**Surveillance** --- The observation of an area or space for the purpose
of determining the position and movements of craft or vehicles in that
area or space.

**Survey** --- The act of making measurements to determine the relative
position of points on, above, or beneath the earth\'s surface.

**Surveying** --- That branch of applied mathematics which teaches the
art of accurately determining the area of any part of the earth\'s
surface, the lengths and directions of the bounding lines, the contour
of the surface, etc., and accurately delineating the whole on a map or
chart for a specified datum.

**Terminal** --- A phase of navigation covering operations required to
initiate or terminate a planned mission or function at appropriate
facilities. For airborne missions, the terminal phase is used to
describe airspace in which approach control service or airport traffic
control service is provided.

**Terminal Area** --- A general term used to describe airspace in which
approach control service or airport traffic control service is provided.

**Time Interval** --- The duration of a segment of time without
reference to where the time interval begins or ends.

**Universal Transverse Mercator (UTM) Grid** --- A military grid system
based on the Transverse Mercator projection applied to maps of the
Earth\'s surface extending to 84°N and 80°S latitudes.

**Vehicle Location Monitoring** --- A service provided to maintain the
orderly and safe movement of platforms or vehicles. It encompasses the
systematic observation of airspace, surface, and subsurface areas by
electronic, visual or other means to locate, identify, and control the
movement of platforms or vehicles.

**World Geodetic System (WGS)** --- A consistent set of parameters
describing the size and shape of the earth, the positions of a network
of points with respect to the center of mass of the earth,
transformations from major geodetic datums, and the potential of the
earth (usually in terms of harmonic coefficients).

**APPENDIX C**

**GPS USER\'S WORKSHOP AND USER SURVEY**

Listed below are the Federal agencies and organizations invited to
attend the GPS User\'s Workshop conducted in March 1994 by the U.S. Army
Topographic Engineering Center and the Institute for Telecommunication
Sciences:

> Advisory Commission on Intergovernmental Relations
>
> Agency for International Development
>
> Arms Control & Disarmament Agency
>
> Bureau of Census
>
> Bureau of Indian Affairs
>
> Central Intelligence Agency
>
> Defense Mapping Agency
>
> Department of Agriculture
>
> Department of Energy
>
> Department of Housing & Urban Development
>
> Department of Justice
>
> Department of Labor
>
> Department of State
>
> Environmental Photographic Interpretation Center
>
> Federal Aviation Administration
>
> Federal Bureau of Investigation
>
> Federal Communications Commission
>
> Federal Emergency Management Agency
>
> Federal Highway Administration
>
> Federal Railroad Administration
>
> Federal Transit Administration
>
> Fish and Wildlife Service
>
> General Services Administration
>
> Geographic Data Service Center
>
> Immigration and Naturalization Service
>
> International Boundary Commission
>
> International Boundary and Water Commission, U.S. & Mexico
>
> Internal Revenue Service
>
> Interstate Commerce Commission
>
> Marine Corps Operational Test and Evaluation Activity
>
> Maritime Administration
>
> Minerals Management Service
>
> National Park Service/National Biological Survey
>
> National Aeronautics and Space Administration

National Geodetic Survey

National Institute of Standards and Technology

National Capital Planning Commission

National Railroad Passenger Corp.(AMTRAK)

National Oceanic and Atmospheric Administration

National Science Foundation

National Marine Fisheries Service

National Transportation Safety Board

National Telecommunications and Information Administration

Naval Oceanographic & Meteorological Command

Naval Operational Test and Evaluation Force

Nuclear Regulatory Commission

Office of Engineering and Technology

Office of Technology Management

Office of Management and Budget

Office of Science & Technology

Office of the Federal Coordinator for Meteorological Service and Support
in Research

Panama Canal Commission

Peace Corps

St. Lawrence Seaway Development Corporation

Soil Conservation Service

Tennessee Valley Authority

U.S. Customs

U.S. Geological Survey

U.S. Air Force Operational Test and Evaluation Command

U.S. Army Corps of Engineers

U.S. Army Test and Evaluation Command

U.S. Army Transportation School

U.S. Environmental Protection Agency

U.S. Coast Guard

U.S. Postal Service

U.S. Naval Observatory

U.S.D.A. Forest Service

These agencies and organizations were also asked to complete a survey
intended to help the study team identify requirements for augmented GPS
services. A copy of the survey begins on the following page.

**FEDERAL REQUIREMENTS SURVEY FOR**

**AUGMENTED GPS SERVICES**

1.  **[INTRODUCTION]{.underline}**: A survey is being performed to
    determine the requirements for augmented Global Positioning System
    (GPS) services. Many Federal Organizations have requirements to
    provide or use augmented GPS services and/or support state and local
    governments or private citizens needing augmented GPS services. It
    is requested that organizations having or projecting needs to
    provide or use augmented GPS services for the next 20 years, or
    which have constituents having such needs, complete the following
    questionnaire.

> If there are multiple classes or phases of service required, please
> identify the differing requirements for each. If an organization is
> cognizant of widely divergent requirements, a separate questionnaire
> should be completed for each.
>
> Definitions for minimum performance requirements are consistent with
> those in the Global Positioning System Standard Positioning Service
> Signal Specification. Unless otherwise requested, please provide
> requirements for the service, not individual user equipments.

2.  **[ORGANIZATION DATA]{.underline}**:

    1.  Organization:

    2.  Address:

    3.  Point of Contact/Title:

    4.  Voice Phone: FAX:

    5.  Electronic mail address:

3.  **[DESCRIPTION]{.underline}**: Provide a brief description of your
    functional requirements for augmented GPS service.

4.  **[COVERAGE AREA]{.underline}**: Specify the geographic area(s)
    which must be covered by the augmented GPS service. If there are
    requirements for different levels of service (e.g. en route
    navigation and landing approach), provide the coverage areas for
    each. If multiple, specific sites must be covered, indicate the
    number of sites as well as coverage area. Stand-alone GPS provides
    global coverage.

5.  **[COVERAGE]{.underline}**: Coverage is the probability the system
    will provide adequate signal coverage of the coverage area assuming
    the complete system is operating within specification limits. The
    GPS coverage standards are predicated on having 4 or more satellites
    in view, above a 5 degree elevation mask, with no local obscura,
    with 4 satellites providing a Position Dilution of Precision (PDOP)
    ≤ 6, and the constellation having 24 operational satellites located
    in accordance with the almanac. The standard is that coverage will
    be ≥ 99.9% over any 24 hour period when averaged over the globe.
    Coverage may be ≥ 96.9% at the worst location over any 24 hour
    period. Systems requiring greater levels of coverage must be
    augmented. Augmented systems may have different constraints (e.g.
    redundant satellites, different geometric limits, etc.) and coverage
    requirements than GPS.

Specify coverage requirements and constraints.

6.  **[LOCAL COVERAGE LIMITATIONS]{.underline}**: GPS coverage is
    predicated on having a clear view of the satellites, with no local
    signal degradation, and optimal operation of the user\'s receiver.
    Specify the spatial and temporal characteristics of local
    conditions, such as obstructions and heavy foliage, which may reduce
    coverage of the augmented system. Include conditions which may
    affect other segments of the system (e.g. terrestrial
    communications) as well as GPS.

7.  **[AVAILABILITY]{.underline}**: Availability is the probability that
    service, meeting the coverage constraints, will be available to the
    user. Availability is reduced when some portion of the system is
    removed from service for maintenance or through malfunction. GPS
    service availability standards are: ≥ 99.85% for a typical 24 hour
    period, averaged over the globe; ≥ 99.16% for a typical 24 hour
    period, at the worst case point on the globe; ≥ 95.87% for the worst
    case 24 hour period, averaged over the globe; and ≥ 83.92% for the
    worst case 24 hour period, at the worst case point on the globe.

Specify service availability requirements and constraints.

8.  **[RELIABILITY]{.underline}**: Reliability is the probability that
    the service error is less than or equal to a threshold value,
    assuming the coverage and availability criteria are satisfied. The
    GPS SPS service reliability threshold is not to exceed 500 meters
    horizontal error. The service reliability standards are: ≥ 99.7%,
    based on a measurement interval of a year and average of daily
    values over the globe; and ≥ 99.79% based on the yearly average of
    daily values for the worst case point on the globe.

Specify service reliability requirements and constraints.

9.  **[FAILURE NOTIFICATION RESPONSE TIME]{.underline}**: Failure
    notification response time is the time between the time a service
    element fails (becomes unreliable) and the time a user is notified
    the element has failed (i.e. made unavailable). GPS failure
    notification response time may be several hours.

Specify maximum allowable and statistical failure notification response
times.

10. **[OTHER INTEGRITY REQUIREMENTS]{.underline}**: Specify any service
    integrity requirements not covered above.

11. **[ACCURACY]{.underline}**: Accuracy is a statistical measure of how
    consistently the solution conforms to the expected value. Different
    users may view accuracy in different ways. GPS SPS accuracy
    standards have been established for predictable accuracy, repeatable
    accuracy, relative accuracy, and time transfer accuracy. Accuracy
    standards are predicated on the coverage, availability and
    reliability constraints having been met. The GPS accuracy standards
    also assume optimum user receiver operation with no signal
    degradation by local multipath, foliage attenuation, etc.

> Predictable accuracy represents how well the position solution
> conforms to \"truth.\" Truth is defined as any location accurately
> surveyed with respect to the WGS 84 coordinate system. GPS SPS
> predictable accuracy standards are: ≤ 100 meters horizontal error, 95%
> of the time; ≤ 156 meters vertical error, 95% of the time; ≤ 300
> meters horizontal error, 99.9% of the time; and ≤ 500 meters vertical
> error, 99.9% of the time.
>
> Repeatable accuracy represents how well a user can return to a
> position previously established with the same system. GPS SPS
> repeatable accuracy standards are: ≤ 141 meters horizontal error, 95%
> of the time: and ≤ 221 meters vertical error, 95% of the time.
>
> Relative accuracy represents how well a user position solution relates
> to a position solution obtained at another location using the same
> system at approximately the same time. For GPS, an additional
> constraint is that the solutions at both locations employ the same
> signals from the same set of satellites. The GPS SPS relative accuracy
> standards are: ≤ 1.0 meter horizontal error, 95% of the time; and ≤
> 1.5 meters vertical error, 95% of the time.
>
> Time transfer accuracy represents how well a service user can relate
> receiver time to Universal Coordinated Time (UTC) as disseminated by
> the U.S. Naval Observatory. The GPS SPS time transfer accuracy
> standard is ≤ 340 nanoseconds time transfer error (95%).
>
> Specify type(s) of accuracy required (for position, velocity and
> time), quantitative accuracy requirements, and statistical basis for
> the requirements. (NOTE: The GPS SPS Signal Specification does not
> specify velocity performance standards.)

12. **[PROCESSING TIMELINESS (POST-PROCESSING, NEAR-REAL-TIME, OR
    REAL-TIME):]{.underline}** Describe how long after measurements are
    made that the positional result is required by the application.

13. **[GPS METHOD:]{.underline}** GPS methods include absolute point
    positioning, kinematic, real-time On-The-Fly, etc. What GPS method
    is involved in meeting this application?

14. **[OBSERVATIONS TYPES:]{.underline}** Describe whether this
    application requires carrier or code observations.

15. **[FREQUENCY of OBSERVATIONS:]{.underline}** Describe whether this
    application requires single or dual frequency (i.e., L1, L1/ L2).

16. **[OTHER MEASUREMENT CRITERIA:]{.underline}** For example, is full
    wavelength L2 required or is L2 squaring sufficient?

17. **[DATA TYPES]{.underline}**: Specify the data types which must be
    provided by the augmented GPS service. Include data requirements for
    ancillary functions as well as for the primary service.

18. **[DATA ARCHIVING]{.underline}**: Specify any requirements for data
    archiving. Include: purpose (e.g. post-processing survey, liability
    records, system performance evaluation, etc.); types of data
    required; frequency of data recording; and retention time.

19. **[DATA COMMUNICATIONS]{.underline}**: Specify any preferred
    communications methods, frequency bands, modulation methods, etc.
    for communicating augmented GPS service data. Provide the rationale
    for any preferences. Include requirements for communication of
    auxiliary data as well as primary positioning service data. Identify
    any unacceptable communications methods. Include any requirements
    for allowable error rates which aren\'t covered by the service
    reliability requirements.

20. **[UPDATE RATE AND LATENCY]{.underline}**: Update rate is the
    frequency of transmission of similar sets of data (e.g. pseudo-range
    corrections for nominally the same set of satellites) needed to
    provide the minimal acceptable level of service. It is not
    necessarily the required solution output rate for the user
    equipment. Latency is the time between the time of applicability of
    the data and the time the data is actually received by the user and
    is available for use. Specify any requirements for data update rates
    and latency.

21. **[SAMPLING RATE:]{.underline}** What is the time period between raw
    measurement recordings that is required for this application? (Not
    to be confused with the output rate of position fixes).

22. **[COMMAND AND CONTROL]{.underline}**: Specify any system command
    and control requirements.

23. **[SECURITY/LIMITED ACCESS]{.underline}**: Identify and provide
    rationale for any security requirements or needs to limit access.

24. **[COST RECOVERY:]{.underline}** Identify any cost recovery
    requirements or funding constraints for providing augmented GPS
    services.

25. **[USER EQUIPMENT CONSTRAINTS]{.underline}**: Identify and provide
    rationale for any user equipment constraints, such as size, weight,
    power consumption, cost, performance certification, specific
    integration requirements, etc.

26. **[STANDARDS/INTEROPERABILITY]{.underline}**: Identify and provide
    rationale for any Government and/or industry standards with which
    the augmented GPS service must comply or be compatible or other
    systems with which it must be interoperable.

27. **[DEPLOYMENT SCHEDULE]{.underline}**: Provide the desired
    deployment schedule for the augmented GPS service. Identify any
    legal or regulatory requirements which impose schedule constraints.

28. **[ADDITIONAL USERS]{.underline}**: The potential user base for the
    augmented GPS service is large and varied. This study is focusing on
    the Federal users. List Federal user(s) that your organization
    interfaces with that is not represented today but should be
    contacted to be surveyed. Due to the limitations of time, this study
    is limited to focus on the Federal user. If your organization
    interfaces with state and/or local government(s) that would be
    affected by or benefit by the implementation of an augmented
    service, list those. Given time, these may also be surveyed.

29. **[ADDITIONAL COMMENTS:]{.underline}**

**APPENDIX D**

**GPS BACKGROUND**

The Global Positioning System (GPS) is a spaced-based radionavigation
system which is managed for the Government of the United States by the
U.S. Air Force, the system operator. GPS was originally developed as a
military force enhancement system and will continue to play this role.
However, GPS also has significant potential to benefit the civilian
community in an increasingly large number and variety of applications.
In an effort to make GPS service available to the greatest number of
users while ensuring that national security interests of the United
States are protected, two GPS services are provided. The Precise
Positioning Service (PPS) provides full system accuracy primarily to
U.S. and allied military users. The Standard Positioning Service (SPS)
is designed to provide a less accurate positioning capability than the
PPS for civilian and all other users throughout the world.

**D.1  System Description**

GPS has three major segments: Space, Control, and User.

The GPS Space Segment is composed of 24 satellites in six orbital
planes. The satellites operate in circular 20,200 km (10,900 nautical
mile) orbits at an inclination angle of 55 degrees and with a 12-hour
period. The satellites are arranged in orbit so that a minimum of 5
satellites are in view at any point on the earth\'s surface.

The GPS Control Segment has five monitor stations and three ground
antennas with uplink capabilities. The monitor stations use a GPS
receiver to passively track all satellites in view and accumulate
ranging data from the satellite signals. The information from the
monitor stations is processed at the Master Control Station (MCS) to
determine satellite clock and orbit states and to update the navigation
message of each satellite. This updated information is transmitted to
the satellites via the ground antennas, which are also used for
transmitting and receiving satellite health and control information.

The GPS User Segment consists of user equipment which can be applied in
a variety of configurations and integration architectures. User
equipment includes an antenna and receiver-processor to receive and
compute navigation solutions to provide positioning, velocity, and
precise timing to the user.

**D.2  Data Link Characteristics**

Each satellite transmits three separate spread spectrum signals on two
L-band frequencies, Ll (1575.42 MHz) and L2 (1227.6 MHz). Ll carries a
Precise P(Y) Pseudo-Random Noise (PRN) code and a Coarse/Acquisition
(C/A) PRN code; L2 carries the P(Y) PRN code. (The Precise code is
denoted as P(Y) to identify that this PRN code can be operated as either
an unencrypted "P" or an encrypted "Y" code configuration.) Both PRN
codes carried on the L1 and L2 frequencies are phase-synchronized to the
satellite clock and modulated (using modulo two addition) with a common
50 Hz navigation data message containing satellite clock and ephemeris
information. Bandwidth and received power characteristics for each of
the signals are summarized in Table D-1 below.

Table D-1.  Bandwidth and Received Power Characteristics for GPS Signals

  ---------- ---------------- ---------------- ---------------------------
  Channel    Center Frequency Bandwidth        Minimum Received Power

  L1 C/A\*   1575.42 MHz      2.046 MHz        -160.0 dBW

  L1 P(Y)    1575.42 MHz      20.46 MHz        -163.0 dBW

  L2 P(Y)    1227.6 MHz       20.46 MHz        -166.0 dBW
  ---------- ---------------- ---------------- ---------------------------

\*SPS signal

In order to support civilian GPS applications, the SPS user is
guaranteed system access through the use of the L1 C/A signal while the
P(Y) code on L1 and L2 is reserved for PPS requirements. System accuracy
for the SPS user is maintained through the use of Selective Availability
(SA). SA is the means by which the U.S. intentionally degrades full
system accuracy to an unauthorized user (i.e., SPS users) by corrupting
satellite clock and ephemeris data. SA was developed by the U.S. to
ensure that an adversary does not use GPS as a military force enhancer
against the U.S. and its allies.

The navigation data contained in the signal is composed of satellite
clock and ephemeris data for the transmitting satellite plus GPS
constellation almanac data, GPS to UTC time offset information, and
ionospheric propagation delay correction parameters for single frequency
users. The entire navigation message repeats every 12.5 minutes. Within
this 12.5-minute repeat cycle, satellite clock and ephemeris data for
the transmitting satellite is sent 25 separate times so that the minimal
data required to perform navigation fixes repeats every 30 seconds.

**D.3  Acquisition Time**

Receiver acquisition time from a cold start varies between receiver
manufacture designs and surrounding environmental conditions (i.e.,
dynamics, terrain masking). Nominally, a receiver\'s time to first fix
is 1 to 3 minutes. Once a position fix is established, the receiver fix
rate is continuous with nominal 1 Hz update rates.

**D.4  Computational Requirements**

The concept of GPS position determination is based on the intersection
of four separate vectors each with a known origin and a known magnitude.
Vector origins for each satellite are computed based on satellite
ephemeris data that are continuously transmitted by the satellite (every
30 seconds). Vector magnitudes are calculated based on signal
propagation time delay as measured from the transmitting satellite\'s
PRN code phase delay. Given that the satellite signal travels at nearly
the speed of light, the receiver is able to perform ranging measurements
between the individual satellite and the user by multiplying the
satellite signal propagation time by the speed of light.

These measurements are combined to yield system time and the user\'s
three-dimensional position and velocity with respect to World Geodetic
System, 1984 (WGS-84) Earth Centered-Earth Fixed (ECEF) coordinates.
Standard coordinate transformations are then performed within the
receiver to provide user position and velocity in local coordinates
(e.g., North American Datum 1987 latitude, longitude, and altitude
coordinates).

A receiver requires four simultaneous measurements from four separate
satellites to determine position in three dimensions and time. The
receiver uses the four simultaneous measurements to yield four
mathematically linearized equations with four unknowns from which the
four unknowns can be solved (e.g., latitude, longitude, altitude, and
time). If the user needs only two-dimensional positioning and time
determination, only three simultaneous satellite measurements are
required for three equations and three unknowns (latitude, longitude,
and time). If the user needs only time determination, only one satellite
measurement is required for one equation and one unknown (time).

**D.5  GPS SPS Performance**

SPS is the standard specified level of positioning and timing accuracy
that is available, without restrictions, to any user on a continuous
worldwide basis. The accuracy of this service is established by the DOD
and DOT based on U.S. security interests. SPS performance levels are
documented in the *Global Positioning System Standard Positioning
Service Signal Specification* \[1\]. This specification states that at a
minimum, the SPS user is guaranteed performance as follows:

> **Coverage:**  The probability that four or more GPS satellites are in
> view over any 24-hour interval, with a PDOP of 6 or less, with at
> least a 5 degree elevation mask angle is at least 99.9% (global
> average).

**Availability:**  Provided there is coverage as defined above, the SPS
will be available at least 99.85% of the time (global average).
Availability of the GPS signals is subject to accidental failure of one
of the satellites and to regularly scheduled maintenance periods. It is
estimated that there will be an average of 1 accidental failure per year
with a maximum of perhaps 3. Resolution might be a simple remote
reprogramming of the system, but it also might require replacement by
spare satellites that have been parked in orbit or that must be newly
launched. Clearly such replacements could take quite a lot of time, but
the purpose of having 24 satellites in the first place is that even with
one or two out of service the remainder should still supply adequate
signals. When a failure occurs, the satellite software will usually
respond immediately to take that signal out of service. On occasion,
however, this may require manual operation and that in turn may require
as much as 6 hours. Regular maintenance should take one satellite out of
service about every 10 days. Maintenance operations may require up to 24
hours.

**Reliability:**  Conditioned on coverage and service availability, the
probability that the horizontal positioning error will not exceed 500
meters at any time is at least 99.97% (global average).

**Accuracy:**  SPS provides a predictable positioning accuracy of 100
meters (95%) horizontally and 156 meters (95%) vertically and time
transfer accuracy to UTC within 340 nanoseconds (95%).In reality,
however, accuracy is partially dependent on the design of the GPS
receiver and some manufacturers have achieved considerably better
results through the use of predictive filters, carrier-phase reception,
and (L1/L2) comparisons. Such steps make the receivers more complicated
(and more expensive) but they point out the fact that their development
is an ongoing process with a promising future.

**D.6  GPS PPS Performance**

PPS is the most accurate direct positioning, velocity, and timing
information continuously available, worldwide, from the basic GPS. This
service is limited to users specifically authorized by the U.S. PPS
coverage, availability, and reliability performance is identical to the
SPS. PPS provides a predictable positioning accuracy of at least 22
meters (95%) horizontally and 27.7 meters (95%) vertically with a time
transfer accuracy to UTC within 200 nanoseconds (95%).

**D.7  References**

\[1\] U.S. Department of Defense, *Global Positioning System Standard
Positioning Service Signal Specification*, Washington, DC, November
1993.

**APPENDIX E**

**JAMMING AND SPOOFING**

**OF AUGMENTED GPS**

The inherent precision, coverage, and availability provided by a
Federally-operated Augmented GPS (AGPS) architecture will potentially
make it a national asset that is quickly embedded into the U.S.
infrastructure. Since GPS Augmentations will provide accuracies of 1-5
meters (95%), versus GPS SPS accuracies of 100 meters (95%),
applications employing GPS augmentations will be much more sensitive to
system perturbations than those applications using the basic GPS SPS.

Currently identified AGPS applications encompass very large and diverse
user populations such as precision landing systems, air traffic control,
railway management, inland waterway navigation, harbor/harbor approach
navigation, and telecommunication systems. Service disruptions or
undetected errors in such applications can result in risk to life,
property, and/or U.S. commerce. Consequently, consideration needs to be
afforded the following in fielding and operation of Federal
augmentations:

> • Service Disruption: What risk is there to disruptions to the U.S.
> infrastructure and its ability to conduct normal commerce as a result
> of a service failure or interruption? How severe and what additional
> risks are incurred due to service failures or interruptions?
>
> • Environmental Impact: What risk is there for ecological disasters
> occurring due to a service failure or interruption?
>
> • Property Damage: What risk is there for property damage occurring
> due to a service failure or interruption?
>
> • Human Life: What risk is there to human life due to a service
> failure or interruption?
>
> • Liability: What are the liability implications for providing a
> radionavigation and positioning service?

Vulnerabilities must be recognized and quantified so that appropriate
countermeasures can be developed. Foremost of these is the vulnerability
of GPS and its augmentations to jamming and spoofing.

**E.1 Jamming and Spoofing**

The term "jamming" refers to intentional and unintentional radio
frequency (RF) interference of transmitted signals received by a user.
The term \"spoofing\" refers to the transmission of counterfeit signals
to provide undetectable falsification of service.

Unintentional jamming includes known RF sources that coincidentally
interfere with the GPS or AGPS signal. Typical sources that can
unintentionally interfere with GPS or AGPS systems include mobile
communication systems and television station transmitters.

Intentional jamming and spoofing sources include signals deliberately
transmitted to interfere with the GPS or AGPS signal. The objective of
an intentional jammer or spoofer is to cause havoc in system
applications resulting in total denial or mistrust of the system.
Jamming and spoofing can be accomplished using information from open
literature which defines signal format and data structure and
off-the-shelf hardware and software. Persons or groups who might want to
intentionally jam or spoof GPS or AGPS systems would include hackers,
extortionists, and terrorists.

**E.1.1 GPS Jamming**

The GPS uses a spread spectrum signal design which provides some
inherent resistance to jamming. Spread spectrum signals provide a means
for a receiver to enhance the power of a GPS signal spread over a given
frequency band, while conversely dispersing a high power jamming signal
transmitted at a given frequency. Several GPS augmentations have
identified a spread spectrum signal structure transmitted on L1 similar
to that used by GPS.

However, the GPS signal is vulnerable to jamming. The ability to jam a
GPS signal is predominately a function of a jammer's radiated power and
the distance between the receiver and jamming source. Since GPS received
power levels are very low, radiated power from the jamming source can be
fairly low and still affect fairly large areas.

Upon entering a jammer's sphere of influence, a typical GPS receiver
will initially loose carrier lock, but maintain code lock, which may
result in aberrant position solutions. Once a receiver is totally within
a jammer's sphere of influence, the GPS receiver will loose code lock
resulting in total loss of GPS positioning capability. Even if an AGPS
system is not using GPS's L1 frequency, all AGPS services will be
disrupted since they all rely on GPS signal availability.

As GPS receivers become more numerous, concerns over identifying and
mitigating RF interference sources continue to increase. Tests conducted
in England have demonstrated that GPS users can be jammed to a range of
95 kilometers by a 1 Watt jammer. Field tests have demonstrated that
FCC-compliant television transmitters output signal harmonics that can
unintentionally jam GPS signals. Test results indicate that, depending
on the television channel and emitted power, a television station can
interfere with GPS receivers within a 16 kilometer radius for land users
and even greater distances for airborne users.

**E.1.2 GPS SPS Spoofing**

A spoofer must emulate a GPS signal and "capture" users within a
specific target area. To "capture" a user, the spoofer must manage
signal levels received at the user location. Spoofer power must be high
enough to ensure that the receiver will lock and track on the spoofed
signal and yet low enough so as not to be detectable as a spoofer or act
like a jammer. Additionally, "capturing" a GPS receiver requires that
the spoofer\'s code phase coincide with the time of arrival of the code
phase of the real GPS satellite at the user location. Due to this
time-of-arrival constraint, normal expectations are that a spoofer would
spoof only one satellite at a time rather than managing complicated
time-of-arrival constraints for two or more satellites.

Once \"captured,\" the spoofer introduces errors into the user receiver
with either falsified data contained within the spoofer's navigation
message, slewing of the code phase, or both. Slewing the code phase also
increases the number of potential \"captured\" user sets as the signal's
code phase is swept back and forth to coincide with GPS signals over a
given area.

Provided that a spoofer is able to \"capture\" a user receiver, errors
introduced by the spoofer may or may not affect the receiver\'s
navigation solution. A spoofer\'s ability to introduce errors in the
user navigation processing is dependent on whether the spoofed satellite
was selected within the receiver as one of the satellites used in
computing the navigation solution. Since most receiver manufacturers use
common logic for satellite selection, a spoofer using the same satellite
selection logic has a high probability of selecting a satellite being
used in the GPS receiver's navigation solution. However, assuming that a
spoofer is transmitting corrupted data for one satellite at a time, GPS
receivers using integrity checking algorithms, such as Receiver
Autonomous Integrity Monitoring (RAIM), would most likely detect the
spoofed signal as a satellite integrity failure and reject it from
inclusion in the navigation solution.

**E.1.3 AGPS Spoofing**

Since GPS Augmentations rely on some type of a Differential GPS (DGPS)
link, spoofing GPS Augmentations may be more effective than spoofing GPS
SPS. For local area DGPS (LADGPS) systems, the spoofer would replicate
and transmit a \"LADGPS\" signal with falsified data to users in the
surrounding area. \"Capturing\" LADGPS sets would entail that the
spoofing signal be at high enough power to mask out and override the
true LADGPS signal level at the receiver. Unlike GPS SPS, no
time-of-arrival complexities are involved since the LADGPS signal used
does not require code phase synchronization. For GPS Augmentations that
provide a ranging capability (e.g., pseudolites and WAAS), the same
time-of-arrival constraints as those identified for GPS SPS would apply.

The spoofer introduces errors into the AGPS receiver by transmitting
false pseudorange corrections for all satellites in view using the
appropriate AGPS format and signal structure. Unlike a GPS SPS spoofer
that imitates only one GPS satellite, an AGPS spoofer can corrupt data
for every satellite visible. Doing so ensures that corrupt navigation
solutions will result regardless of which satellites the receiver uses
in its navigation solution. In addition, spoofing all satellites in view
may bypass commonly used integrity detection algorithms used within AGPS
receivers, hence the spoofer is able to falsify service and remain
undetected.

**E.2 Conclusion**

DOT's January 1994 Strategic Plan has established the goal to "Promote
Safe and Secure Transportation." To meet this objective, the plan
specifies that DOT will "Identify and implement new measures to enhance
security on all modes of transportation to achieve personal security and
national security goals."

DOT should continue to evaluate system risks and appropriate measures
needed to ensure safe and reliable augmentation services. Further, DOT,
with the assistance of DOD, should test and evaluate measures to
mitigate the susceptibility of Federally provided augmentation systems
to all forms of interference including jamming and spoofing.

**APPENDIX F**

**EVALUATION OF DGPS DATA FORMATS**

The purpose of this appendix is to examine existing Radio Technical
Commission for Maritime Services (RTCM) and RTCA, Inc. data formats and
determine if a common data format can and should be developed which
would meet the requirements of users as well as provide an efficient
means of transmitting augmented GPS data.

Differential GPS service providers must address four issues regarding
the transmission of differential corrections:

> 1\) Select an appropriate communications link.
>
> 2\) Interface the link with the GPS receivers at the reference and
> user stations.
>
> 3\) Choose a modulation technique.
>
> 4\) Choose the signal and data format.

The following discussion addresses the fourth issue of this list.

**F.1 Background**

In selecting a data format, several factors must be considered. These
include limitations imposed upon the format by the data link chosen,
such as:

> 1\) Bandwidth --- Information rate and data content define the
> bandwidth required.
>
> 2\) Range of coverage --- Correction data required varies as a
> function of the size of the area covered. A local area system usually
> has a single reference station and reports on all satellites it can
> view. Typically such systems assume that ephemeris and atmospheric
> errors in their service area are effectively the same for the user and
> reference station. A wide area system, however, will have to report on
> those satellites that can be seen by any user within its wide service
> area. This may be all GPS satellites plus geostationary satellites. In
> addition, since some error components are spatially and temporally
> decorrelated, a wide area system will need to provide corrections for
> error components such as ionospheric decorrelation, ephemeris error,
> and clock errors.
>
> 3\) Update rate --- Update rate is a function of the length of time
> that correction data is considered valid, the dynamics of the user
> platform, and the level of accuracy the user requires.

4\) Noise characteristics --- Noise characteristics and effects are a
function of frequency. A low frequency transmission (say below 30 MHz)
requires a different message structure to accommodate lower data rates
and noise characteristics. For communication frequencies above 30 MHz,
the noise is relatively low and is white Gaussian in nature. At the
lower frequencies the noise, such as that caused by lightning, is
impulsive and non-Gaussian. The effects of noise are an important
consideration in developing coding techniques to optimize reception.

**F.2 Current Standards**

There are currently two primary data format standards available for the
transmission of differential corrections, RTCM SC-104 and RTCA, Inc.
SC-159.

**F.2.1 RTCM**

RTCM historically has taken the lead in developing standards for use in
the maritime community. RTCM developed the initial draft of the RTCM
SC-104 format in 1985 to meet marine user requirements for augmentation
of GPS. Version 1.0 was published in 1988. The most recent revision,
version 2.1, was published in January 1994 \[1\]. Major factors in the
development and ongoing evolution of RTCM have been the desire to
maintain a \"GPS-like\" format data structure and to capitalize on the
existing radiobeacon infrastructure.

**F.2.2 RTCA, Inc.**

RTCA, Inc. performs a similar function for the aviation community that
RTCM does for the marine community. RTCA, Inc. is developing formats for
FAA\'s planned Wide Area Augmentation System (WAAS) and FAA LADGPS
systems. A draft specification for the WAAS format was published in 1994
\[2\]. The RTCA, Inc. Special Category (SCAT) I format for LADGPS
systems was published in April 1993 \[3\].

In contrast with LADGPS systems which primarily provide pseudorange
corrections from a single reference station, the WAAS also contains
information from an integrity and reference monitoring and processing
network. Data is collected from reference and integrity monitor sites
which are widely dispersed geographically. Measured data is processed to
determine integrity, differential corrections, residual errors, and
ionospheric delay information for each monitored satellite. The stations
also provide timing references for the establishment of WAAS system
time. This information is superimposed on a GPS-like signal and
broadcast over a wide area from geostationary satellites.

The WAAS Minimum Operational Performance Standard (MOPS) specifies a 250
bit block which is transmitted in one second. Each block contains an
8-bit part of a distributed preamble, a 6-bit message type, a 212-bit
data field and 24-bit Cyclic Redundancy Check (CRC) parity. The block
length is consistent with the required time to alarm and any message
type can occur in any given one-second interval. The start of the first
8-bit part of every other 24-bit distributed preamble will be
synchronous with the 6-second GPS subframe epoch to within the overall
WAAS performance requirements. The minimum message set to be decoded by
the WAAS receiver for en route and terminal operations is shown in Table
F-1 below. Each message type occupies an integral number of 250 bit
blocks.

Table F-1. Minimum Message Set Based on RTCA, Inc. MOPS

  -------------- --------------------------------------------------------
  Type           Contents

  0              Don\'t use this GEO for anything; for WAAS testing.

  1              PRN mask assignments, set up to 52 of 210 bits.

  2              Fast corrections (clock corrections).

  9              GEO ephemeris message (X, Y, Z, time, etc.).

  12             WAAS network/UTC offset parameters.

  17             GEO satellite almanacs.

  18 to 23       Ionospheric grid point mask numbers 1 to 5.

  24             Mixed fast corrections/long-term satellite error
                 corrections (clock/ephemeris corrections).

  25             Long-term satellite error corrections.

  26             Ionospheric error corrections.
  -------------- --------------------------------------------------------

An important difference between the WAAS and LADGPS is the fact that the
WAAS must provide information on all navigation satellites in the
footprint of the geostationary satellite broadcast. This could be most
all GPS and GLONASS satellites plus geostationary satellites; there are
52 slots provided for this, 32 for GPS PRNs. To reduce the overhead
required, a Type 1 message (PRN Mask assignments) is used to define the
\"position\" of the corrections for each satellite in the following Type
2, 24, and 25 messages. Although this mask assignment requires a full
block, it is only broadcast as needed, which is every two to five
minutes or after changes. This reduces the overhead required for message
headers, since satellite ID\'s need not be given for pseudorange and
ephemeris corrections. Message blocks are timed so that the correction
time stamp used in LADGPS formats is not needed, thus reducing the
required data by 13 bits.

Another important difference is that errors resulting from spatial
decorrelation become significant, necessitating the broadcast of
\"slow\" corrections for atmospheric delays and ephemeris errors.
Ionospheric delay corrections are broadcast as vertical delay estimates
at specified ionospheric grid points. The Message Types 18 through 23
are masks for predefined grid points. Message Type 26 contains
ionospheric delays at the Ionospheric Grid points. Using this scheme,
ionospheric corrections require 7 blocks. Ephemeris corrections (Type 24
or 25) require 1 block for 2 satellites. The messages are designed so
that error corrections for satellites with faster changing long term
errors can be repeated at a higher rate than ones with slower changing
long term errors. Corrections for spatial decorrelation require a
significant amount of information, however these are slow corrections
and it is anticipated that they will be broadcast at the rate of once
per 2 to 5 minutes. RTCA, Inc. proposed rules are that long term
satellite error corrections, which are ionospheric delay corrections and
GEO navigation messages shall all be broadcast at a rate sufficient not
to degrade the user\'s first fix capability. It should also be noted
that broadcast messages will not include any explicit tropospheric
corrections.

**F.3 Comparison of RTCM and RTCA-LADGPS Data Formats**

RTCA, Inc. examined the RTCM format several years ago to determine if
the RTCM format could be used to support aviation applications. RTCA,
Inc. determined that the RTCM format could not satisfy all aviation
requirements and that aviation applications would be better served by a
different message format. Specifically, the following information
required by aviation users is not supported by the RTCM format:

> • RTCM does not support an estimator for Selective Availability (SA).
>
> • RTCM was incompatible with ICAO airport identification standards.
>
> • RTCM did not support aviation integrity requirements. RTCM had only
> a 30 bit word for integrity, which was considered insufficient given
> the noise environment on-board an aircraft.
>
> • The RTCM format did not support waypoints for the final approach
> path.

Two other message types unique to RTCA and not represented by the RTCM
format are message types that handle differential corrections during
periods of extremely large range corrections and range-rate corrections
(Message Types 5 and 6).

Other data format differences between RTCM and RTCA, Inc. are shown in
Table F-2.

Table F-2. RTCM/RTCA, Inc. Specifications

  --------------- ------------------------- ------------------------------
                  RTCM                      RTCA

  Station ID      10 bits.                  24 bits to provide
                                            compatibility with ICAO stds.

  Sequence No.    3 bits.                   Not used.

  Acceleration    Not used.                 Replaces RTCM Station Health
  Error Bound                               and can be used by avionics to
                                            estimate error growth (3
                                            bits).

  Station Health  3 bits.                   Not used.

  Scale Factor    1 bit.                    Replaced by Type 5 message.

  Large Range     Provided by scale change  RTCA Type 5 message. In lieu
  Differential    in the Type 1 message.    of RTCA Type 1 message for
  Corrections                               large PRC\'s and RRC\'s.

  Large Range     RTCM Type 5 message       RTCA Type 6 message. Used for
  Differential    specifies IOD. Delta PRCs delta PRC and RRC during
  Corrections     provided by a Type 2      periods of large scale
  when IOD        message.                  corrections.
  changes                                   

  SCAT I Waypoint Not used.                 Replaces RTCM Type 4 message.
  message                                   
  --------------- ------------------------- ------------------------------

**F.4 Summary and Conclusions**

GPS differential corrections, both local and wide area, are broadcast at
many frequencies. The question addressed here has been whether the RTCA,
Inc. SC-159 format and the RTCM SC-104 format could move towards one
single format that could be used by both user communities. Overall,
there seems to be no compelling reasons why in the near term this should
occur. It must be mentioned, however, that due to the similarity between
RTCM SC-104 and the RTCA SC-159 LADGPS formats, there may be some
utility for both user and vendor communities, in devising a single
format at some point in the future. If the systems that transmit a
particular format are used by those outside the community for which that
format was created, there may be cause to revisit this subject. If there
is a move towards a single format, it will most likely come from the
user community.

**F.5 Recommendations**

The development of a data link format is a technically challenging
effort and requires coordination of users and policy makers. This effort
may require several years to complete. For this reason, this study does
not recommend that a common data link format be developed for the
augmented GPS architecture recommended in this study. The time required
for such an effort would significantly impact the scheduled development
and deployment of the recommended architecture, thereby delaying the
delivery of benefits to users.

This study recommends that a working group within an existing
international committee be assigned the responsibility of providing a
forum for any future data link format discussions that may arise in the
user communities.

This working group should address the following three issues:

> 1\) the information content needed to meet user requirements.
>
> 2\) the amount of parity protection to be provided.
>
> 3\) the interface required between the DGPS receivers and the GPS
> receivers.

**F.6 References**

\[1\] Radio Technical Commission for Maritime Services (RTCM) Special
Committee No. 104, *RTCM Recommended Standards for Differential Navstar
GPS Service, Version 2.1*, Washington, DC, January 1994.

\[2\] RTCA Inc., *Minimum Operation Performance Standards for Sensors
Using Global Positioning System/Wide Area Augmentation System, Draft 1*,
Washington, DC, July 1994.

\[3\] RTCA, Inc. Special Committee No. 159, *Minimum Aviation System
Performance Standards DGNSS Instrument Approach System: Special Category
I (SCAT-I)*, Document No. RTCA/DO-217, Washington, DC, August 1993.

**APPENDIX G**

**AUGMENTATION DESCRIPTIONS**

**G.1  Advanced Communications Technology Satellite (ACTS)**

The Advanced Communications Technology Satellite (ACTS) is an
experimental telecommunications satellite which was built for NASA and
launched in 1993. The satellite is a test bed for high gain hopping spot
beams, on-board processing, and Ka-band technologies. These technologies
provide many different capabilities, including the ability to transmit
digital data with a data latency of less than one second at rates up to
hundreds of megabytes per second. The major technology developments of
ACTS include the use of Ka-band frequencies, multiple spot beams,
on-board switching and processing, time division multiple access, and
adaptive forward error correction coding.

**G.1.1 Ka-band**

As data transmission requirements have grown and the geosynchronous arc
has begun to fill with C- and Ka-band satellites, it has become apparent
there is a need for satellite transmissions to move to higher frequency
bands, where more bandwidth is available. The Ka-band (30/20 Ghz) is a
candidate for future use. The Ka-band\'s allotted frequency bandwidth is
twice the size of the combined bandwidths of the C- and Ka-bands
presently used by commercial satellites. It has been predicted that use
of the Ka-band, combined with other technologies used in ACTS could
increase the communications capacity of future commercial satellites by
as much as five times over current technology.

The Ka-band also has the advantages of smaller antenna size for the same
gain and smaller electronic components in general. A drawback of Ka-band
for communications systems has been the high susceptibility to fading in
rain or snow. ACTS dynamically compensates for this fading with Forward
Error Correction coding. Testing underway will show the effectiveness of
this method.

**G.1.2 Spot Beams**

Conventional satellites have antenna patterns which make a footprint on
the surface of the earth which concentrates the satellite power on the
desired area of coverage, for example the Continental United States
(CONUS). However, this beam contouring spreads the satellite signal over
the entire continent, while users may actually be concentrated in a few
densely populated areas. The ACTS uses high gain spot beams, which focus
the satellite signal power only in those areas where it is required, on
demand. The high gain provided by the spot beams allows smaller earth
terminals and frequency reuse, in the manner of cellular systems.

**G.1.3 On-board Processing**

Unlike conventional communications satellites, ACTS has the ability to
downconvert and demodulate the uplink signal down to baseband digital,
then remodulate and upconvert it to 20 Ghz before retransmission down to
earth. This means that the satellite performs as a *regenerative*
repeater, isolating the uplink from the downlink. Thus a degradation on
the uplink may appear as bit errors in the satellite and be
retransmitted, but it does not appear as a weak signal-to-noise ratio
which can be further degraded on the downlink. On a link in which uplink
and downlink carrier to noise ratios are equal, for example, this
results in a 3 dB improvement in the overall link.

Compared to alternative commercial satellite frequency allocations,
Ka-band\'s larger bandwidth allows for higher data transmission rates.
In addition to DGPS data, the anticipated capacity of the ACTS will
support additional data without any negative impact on the performance
of the DGPS. Some examples of additional data that could be supported
include corrections and data from multiple DGPS reference stations,
digital mapping and terrain data, voice communications, FAX, etc. The
satellite\'s on-board processing and on-board switching should reduce
the data latency from the satellite link to a level competing with
digital RF radios, resulting in a higher message update rate than
conventional satellites. True mobile satellite antennas are also
possible through the combined gains of a higher operating frequency and
the higher received signal power achieved by focusing the radiated
signal into the smaller footprints of the hopping spot beams.

**G.2  Global Orbiting Navigation Satellite System (GLONASS)**

The Russian Federation is in the process of developing and implementing
GLONASS to provide signals from space for accurate determination of
position, velocity, and time for properly equipped users. GLONASS will
provide high accuracy and availability to users. Navigation coverage
will be continuous, worldwide, and all-weather. Three-dimensional
position and velocity determinations are based upon the measurement of
transit time and Doppler shift of RF signals transmitted by GLONASS
satellites.

When fully operational, the GLONASS space segment will consist of 24
satellites (21 operational and 3 spares). GLONASS satellites will orbit
at an altitude of 19,100 kilometers with an orbital period of 11 hours
and 15 minutes. Eight evenly spaced satellites are to be arranged in
each of three orbital planes, inclined 64.8 degrees and spaced 120
degrees apart.

The GLONASS ground segment performs satellite monitoring and control
functions and determines the navigation data to be modulated on the
coded satellite navigation signals. The ground segment includes
monitoring stations, a Master Control Station, and an upload station.

Measurement data from each monitoring station is processed at the Master
Control Station and used to compute the navigation data that is uploaded
to the satellites via the upload station. Operation of the system
requires precise synchronization of satellite clocks with GLONASS system
time. To accomplish the necessary synchronization, clock correction
parameters are provided by the Master Control Station.

A navigation message transmitted from each satellite consists of
satellite coordinates, velocity vector components, corrections to
GLONASS system time, and satellite health information. To obtain a
system fix, a user\'s receiver tracks at least four satellite signals,
either simultaneously or sequentially, and solves four simultaneous
equations for the three components of position and time. A position
solution may be derived from three satellites if an external source of
time or altitude is provided.

GLONASS satellites broadcast in two L-band portions of the RF spectrum
and have two binary codes, the C/A code and the P code, and the data
message. GLONASS is based upon a frequency division multiple access
concept. GLONASS satellites transmit carrier signals in different L-band
channels, i.e., at different frequencies. A GLONASS receiver separates
the total incoming signal from all visible satellites by assigning
different frequencies to its tracking channels. The use of frequency
division permits each GLONASS satellite to transmit identical P and C/A
codes.

In GLONASS, the C/A code is modulated onto the L1 carrier only. The P
code is transmitted on both L1 and L2. Receivers designed to operate
with only the C/A code can use only the L1 signal for ranging.
P-code-capable receivers can use both frequencies to measure range. The
use of both frequencies provides a means of correcting for ionospheric
refraction.

The frequency of the GLONASS P code, 5.11 Mhz, is ten times higher than
the frequency of the C/A code, 0.511 Mhz. Since the higher code
frequencies generally provide a better range measuring accuracy than
lower frequencies, GLONASS has a precise mode of operation with the P
code and a less accurate mode using the C/A code. GLONASS is expected to
provide accuracies of 100 meters in horizontal position, 150 meters in
vertical position, 15 centimeters per second in velocity, and 1
microsecond in time.

Each GLONASS satellite transmits navigation data at a rate of 50 bits
per second. The navigation data message provides information regarding
the status of the individual transmitting satellite along with
information on the remainder of the satellite constellation. From a
user\'s perspective, the primary elements of information in a GLONASS
satellite transmission are the clock correction parameters and the
satellite position (ephemeris). GLONASS clock corrections provide data
detailing the difference between the individual satellite\'s time and
GLONASS system time, which is related to UTC.

To provide ephemeris information, GLONASS satellites broadcast their
three-dimensional Earth Centered Earth Fixed (ECEF) position, velocity,
and acceleration for every half-hour epoch. For a measurement time
somewhere between the half-hour epochs, a user interpolates the
satellites\'s coordinates using position, velocity, and acceleration
from the half-hour marks before and after the measurement time. The
resulting ECEF coordinates are referenced to the Soviet Geocentric
System 1985.

**G.3  Inertial Navigation Systems (INS)**

Inertial Navigation Systems (INS) determine change in position by
double‑integration of specific‑force measured by accelerometers.
Gyroscopes are used to track changes in the orientation of the INS
coordinate frame relative to a fixed, non‑rotating coordinate system
known as the inertial coordinate frame. The INS reference frame can be
aligned to local level and north by sensing the direction of gravity and
the earth\'s spin vector or by comparing inertial velocities to external
sources of velocity.

A typical, 3‑axis, INS consists of a cluster of three accelerometers and
three gyroscopes, orthogonally mounted on a stable element, and
associated electronics. There are two generic INS implementations:
gimballed and strapdown. In gimballed systems, the inertial sensor
assembly (ISA) is isolated from vehicle rotations by a set of motor
driven gimbals. The gyroscopically sensed rotation (rate) information is
fed back to the gimbal drive motors to maintain a constant ISA
orientation in space. Additional gimbal torquing may be applied to
orient the ISA in some other desired reference frame (e.g. local level,
north pointing.) In strapdown systems, the ISA is mounted directly to
the vehicle. Changes in orientation of the ISA, sensed by the
gyroscopes, are used to computationally rotate the accelerometer
reference frame to the desired output frame.

While the concept of strapdown INS has been understood for a long time,
advances in computer and gyro technology were required before strapdown
systems became practical. For most applications, modern strapdown
systems are mechanically simpler, lighter weight, smaller, more
reliable, and less expensive than gimballed systems. Gimballed systems
have performance advantages for a few, high accuracy applications
because the gyros must track only the gimbal servo‑loop errors rather
than the total dynamic range of vehicle rotation rates. Angular
accelerations, sensed by the accelerometers, also are minimized by a
gimballed implementation.

An INS may be mechanized with more than three gyros and accelerometers
for redundancy and error checking. Non‑orthogonal mounting or incomplete
implementations (e.g. 2‑axis systems) may be used to meet specific
requirements.

Inertial navigation error sources include: instrument biases, instrument
noise, instrument and platform misalignments, initial position and
velocity errors, and unmodeled gravitational disturbances. Inertial
sensor errors vary greatly depending on instrument quality and basic
technology. Often, external data sources (e.g. altimeters, doppler
radars, and radio navigation aids in aircraft, and odometers and
zero‑velocity stops in ground vehicles) are used to aid INS. Unaided INS
position errors tend to grow with time. High quality INS positions
typically have low latency and small high‑frequency error components.
The low INS high-frequency and bounded GPS low-frequency error
characteristics complement each other.

There are two basic approaches for integrating GPS and INS which are
known as loosely‑coupled and tightly‑coupled. In the loosely-coupled
mechanization, the GPS receiver and the INS maintain separate position
and velocity solutions. Here, GPS positions and velocities are sent to
the INS\'s Kalman filter for error bounding and instrument calibration
(cascading the two navigation filters). Alternately, the outputs of GPS
and INS filters can be combined in a third filter. INS positions and
velocities can be sent to the GPS receiver to aid tracking loops and
satellite acquisition. In a tightly‑coupled system, GPS receiver raw
data are used directly as measurements in a Kalman integration filter
for controlling error in the inertial navigation process, and the
compensated INS velocity is used in the receiver to allow narrower
tracking loops. Estimated system errors include: errors in the INS
nominal position and velocity solution, INS misalignments, gyroscope and
accelerometer errors, GPS receiver clock bias and drift, and, possibly,
external sensor errors such as barometric altimeter bias.

The loosely coupled approach is, in general, less robust under
conditions of multiple satellite obscurations and when high dynamics
occur during periods of jamming. Careful tuning of cascaded filters is
required to prevent stability problems when INS data is fed back to the
GPS receiver. Data latency must be carefully handled when integrating
separate boxes. The industry trend seems to be tightly coupling GPS and
INS within the same box.

GPS provides several benefits to INS:

> • Three-dimensional position and velocity information for position
> initialization, dynamic alignment, and initializing velocities.
>
> • Bounds on INS position error growth.
>
> • Estimation of residual accelerometer and gyroscope instrument biases
> (assuming sufficient satellite availability). During subsequent
> periods of reduced satellite availability, the calibrated performance
> of the INS will be superior to its nominal performance characteristics
> until such time as the random errors and bias drifts exceed the
> nominal bias errors. This may reduce costs by allowing use of
> instruments with less stable bias errors.

INS also provides several benefits to GPS:

> • In cases of total loss of lock (GPS signal) followed by a
> high‑dynamic maneuver, the frequency uncertainty (due to Doppler
> shift) can be large which may preclude timely signal reacquisition.
> INS velocity-aiding data can reduce the frequency uncertainty thus
> increasing the probability of a timely reacquisition.

• The autonomy and rapid response characteristics of INS should enable
detection and isolation of many classes of signal‑in‑space failures that
could not otherwise be corrected in a timely fashion by the control
segment, RAIM or other receiver processing techniques. In addition, the
integration of GPS/INS should prove useful in combatting spoofing.

• The GPS receiver tracking loops must have sufficient bandwidth to
account for phase and frequency changes induced by vehicle maneuvers. At
the same time, they must be narrow enough to limit the level of
interfering noise (e.g. jamming) seen by the phase detector. INS
velocities can be used to \"steer\" the tracking loops for frequency
changes caused by vehicle maneuvers, allowing tracking loop bandwidth
reductions.

• INS can be used to reduce GPS velocity errors resulting from tracking
loop bandwidth limitations and other effects.

The DOD has several embedded GPS/INS systems under development or in
procurement. Commercial GPS/INS integrations are still in a relatively
early stage of development. Recent advances in inertial component and
GPS circuit technology will provide cost reductions currently limiting
this expansion.

**G.4  Sign Posts**

Sign posts are electronic check points at known positions which
dynamically update a moving platform\'s position whenever a sign post is
passed. The updated position can be used either by the user or by a
remote tracking facility. The sign post transmits a signal which is a
formatted message containing the sign post\'s position and other
pertinent information. It is not a ranging signal.

**G.5 Dead Reckoning Systems**

There are many instances where GPS signals will be blocked or become
unusable for the automobile user. This is especially true in the urban
environment or where there is a canopy of trees or in tunnels. In these
cases, dead reckoning can help maintain a continuous fix for the user.
Examples of devices used for dead reckoning include: solid state gyro,
differential odometry, magnetic compasses, magnetic flux gates, and
accelerometers. Dead reckoning has the problem of accumulated distance
error. GPS and dead reckoning can work synergistically to provide a
low-cost navigation system particularly suited for land-based vehicles.
Map matching could be added to both systems which would be integrated
using algorithms which implement Kalman filtering.

The dead reckoning system helps to provide real-time to near real-time
solutions in cases where stand-alone GPS may not be usable for periods
lasting several minutes in \"canyons\" due to terrain, vegetation, and
urban environments. With these two systems, integrity of the navigation
solution is improved because they can check each other for gross errors.

**G.6  Map Matching**

Positions refer to actual mathematical coordinates in some reference
system. Locations refer to a reference relative to land features such as
roads and intersections. Map matching refers to matching the position or
path of a vehicle derived by positioning sensors to a corresponding
position of path in a digital database. The database must be
positionally accurate, geometrically correct, topologically correct,
current, and complete.

**G.6.1  Horizontal Features**

For land vehicles, horizontal features would comprise a digital road
network. With a dead reckoning system, map matching would use previous
position and heading and current position and heading to match its
computed position with the most likely location on the digital road
network. Map matching ensures that if a vehicle is physically on a road
network, it is displayed on the corresponding digital road network.

**G.6.2  Vertical Features**

Map matching using vertical features matches vertical profiles obtained
from sensors with a vertical profile from a database. Sensors measure
the actual terrain profile; a processor \"compares\" what is being
measured with what is stored in the digital database and then makes any
necessary steering adjustments to maintain the proper course.

**G.7  Continuously Operating Reference Stations (CORS)**

**G.7.1  Purpose of CORS**

The purpose of the GPS Continuously Operating Reference Station(s)
(CORS) is to provide code range and carrier phase measurements from
reference stations to users to support after‑the‑fact (often called
post-processing or post-mission) differential positioning of both
stationary receivers and receivers on moving platforms. Currently,
after‑the‑fact differential positioning is the primary operating mode in
the survey and positioning communities. This section summarizes CORS
compatibility requirements. An approved standard defining CORS
requirements will be available in 1995.

GPS range observations from reference stations are used to compute
corrections that allow positioning of stationary receivers at the 1 to
10 meter accuracy level. This is the dominant mode of positioning of
objects and events for input to Geographic Information Systems (GIS).
Almost all high‑accuracy GPS geodetic positioning at the subdecimeter
level is differential positioning relative to permanent or temporary
reference stations using GPS carrier phase measurements and
after‑the‑fact computation of positions. With respect to moving
vehicles, after‑the‑fact differential positioning at the meter level
using code ranges and at the subdecimeter level using carrier phase
ranges are currently employed in such applications as positioning
aircraft in aerial photogrammetry, remote sensing, positioning of ships
in support of bathymetric and geophysical surveys and positioning of
land vehicles to determine road location or the location of objects in
digital imagery.

The CORS network is designed to provide a single network of GPS
reference stations to overcome problems of duplication, inefficiency,
availability, and access. CORS will provide all GPS data types to all
positioning users in a single common format, Receiver Independent
Exchange (RINEX), with continuous monitoring of station position.
Furthermore, sampling rates will be sufficient to satisfy essentially
all users.

**G.7.2  Definition of CORS --- Standards**

The CORS concept includes individual GPS reference stations, located
nationwide. A standardized set of observations are made at these
stations. Included is centralized administration, management, storage,
and distribution of GPS observations. CORS supply these reference
station measurements for all private, academic, and government users in
support of moving and static forms of survey.

The standardized observation set is characterized by:

> • Permanent: 24 hours per day; every day.
>
> • L1 C/A code and carrier measurements.
>
> • Full‑wavelength L2 carrier when L2 available.
>
> • L2 code when L2 available.
>
> • \"All‑in‑View\" GPS satellite tracking.
>
> • 10.0‑degree horizon visibility.
>
> • 5 second sample rate or faster; 1 second desirable.
>
> • Receiver manufacturers\' raw formats.
>
> • 1‑meter L1 code range double differences at epoch.
>
> • GPS observations and Broadcast Message Parameters.
>
> • Weather data desired (Pressure, Temperature, Humidity).
>
> • 15‑days on‑site data holding or central facility transfer.
>
> • 95% hourly measurement sets received (availability).
>
> • 95% hourly sets received have 95% of data (continuity).

The standardized station is characterized by the following parameters:

> • L1 phase center location is official position.
>
> • L2 phase center is desirable.
>
> • NAD‑83 geodetic coordinates (latitude, longitude, ellipsoidal
> height).
>
> • NAVD‑88 orthometric height.
>
> • Accuracies (95%):
>
> latitude - 2 cm.
>
> longitude - 2 cm.
>
> ellipsoidal height - 5 cm.
>
> orthometric height - 10 cm.
>
> • Physical antenna meets wind load guidelines.

**G.7.3  The CORS Central Facility (CCF)**

The CORS Central Facility will accept the data, actively or passively,
from the many CORS facilities. These data will be stored, converted to
additional formats, processed, archived, and distributed.

The observations would be placed online for 20 days, nominally within
one hour of the observations, on direct access hard disk storage. The
original provided data would be in manufacturers\' raw formats. The data
will be converted to RINEX for distribution. Possibly RTCM and RTCA
messages will also be provided, but not in real time. The present method
of user access is via the Internet.

These data will be post-processed by NOAA/NGS. In this way definitive
geodetic vectors will be computed. These daily vectors will be stored
and compared. Should an individual CORS antenna location significantly
change for whatever reason this should be quickly detected. Daily
processing of these vectors will provide an important baseline for
repeatability.

These observational data will be archived in off‑line storage (CD‑ROM)
for a period of time which has not been finalized; one year has been
proposed. After one year, these data may be reduced, filtered, and/or
compressed for long‑term storage. Post-processing solutions will be
stored indefinitely.

**G.7.4  Status and Plans**

The National Geodetic Survey currently operates five prototype CORS
which meet the standards presented here. The differential reference
stations being installed by the U.S. Coast Guard and the U.S. Army Corps
of Engineers will have a CORS capability. The FAA plans to install a
Wide Area Augmentation System (WAAS); the WAAS reference stations are
planned to comply with the CORS standard.

**APPENDIX H**

**COVERAGE AND AVAILABILITY**

**OF LF/MF RADIOBEACONS**

It has been suggested that the U.S. Coast Guard LF/MF Radiobeacon system
be expanded to provide DGPS corrections for CONUS. An important question
to be considered is how many radiobeacons will be required to provide
adequate coverage for DGPS users. To answer this question, from a
technical standpoint, four important issues must be considered:

> 1\) Atmospheric (and man-made) radio noise.
>
> 2\) The ability of minimum shift keying (MSK) receivers to mitigate
> the effects of the noise (i.e., signal to noise ratio required to
> achieve an acceptable bit error ratio).
>
> 3\) LF/MF propagation over ground with varying conductivities.
>
> 4\) Skywave self interference.

In the LF/MF band, the background noise is primarily due to distant
lightning and can be predicted using the methods specified in CCIR
Report 332-3 \[1\]. This does not include effects of nearby electrical
storms (which may add perhaps 20 dB to the noise power) and man-made
impulsive noise which may be expected in large urban areas.

Issues regarding the ability of MSK receivers to mitigate the effects of
impulsive noise are more difficult to quantify. In addition, advances in
MSK receivers will likely reduce bit error ratios (BER) for a given
signal to noise ratio (SNR). Several authors have published measured and
simulated results. For example, data collected at a test bed in Durham,
New Hampshire indicate that for a receiver using \"hard limiting,\" an
SNR exceeding 10 dB is required to provide a 10^-3^ probability of a
\"channel error\" \[2\]. It is further reported that forward error
correction can reduce the required SNR by one half. Published results of
receiver simulations using combinations of nonlinear receiver front ends
(hole puncher, floating envelope clipper) and filters indicate that
BER\'s of less than 10^-3^ may be achieved for SNR\'s near 0 dB \[3\].
Currently, the Broadcast Standard for the USCG DGPS Navigation Service
\[4\] specifies that an MSK Beacon Receiver should achieve a bit error
rate of less than 10^-3^ for an SNR of 7 dB in the 99% power containment
bandwidth of the MSK signal.

Table H-1 shows atmospheric radio noise levels exceeded 5%, 1.0%, and
0.1% of the year at a variety of locations throughout CONUS. Major
cities are used as a convenient method to specify the geographic region
(it should be noted that these values do not include urban noise). For
the purposes of this analysis a receiver bandwidth of 120 Hz is assumed,
which corresponds to the bandwidth containing 99% of the modulation
spectrum for MSK at 100 bps. The actual noise bandwidth to be considered
will, of course, depend on receiver design.

Table H-1. Atmospheric Noise Levels Near Various Cities in CONUS

  ----------------- ----------------- ----------------- -----------------
                    E (dB μV/m)       E (dB μV/m)       E (dB μV/m)
                    exceeded 0.1% of  exceeded 1.0% of  exceeded 5% of
                    the year          the year          the year

  Albuquerque       53.8              41.3              30.8

  Atlanta           52                40.6              31.9

  Boise             43.2              31.9              22

  Chicago           51.5              40.8              32

  Denver            53.9              41.1              30.1

  Fargo             52.6              41.3              30.3

  Houston           52.3              40.3              30.3

  Los Angeles       40.5              39.1              20.2

  Miami             51.5              40.1              30.8

  New York City     40                31                24

  Oklahoma City     55                42.5              31.6

  Phoenix           44.9              32.9              23.2

  Pittsburgh        45                38                28.3

  San Francisco     38.1              27                18.6

  Seattle           37.5              25.6              16.2

  Washington D.C.   42.9              34.2              26.8
  ----------------- ----------------- ----------------- -----------------

The values in the table clearly show that the coastal regions of the
northeast and west are significantly quieter than the southeast and
central/mountain areas. Currently, the USCG standards specify that
radiobeacon coverage extends to the point that the electric field
strength drops to 37.5 dB μV/m (for 100 bps transmission). From the
predicted levels in Table H-1, we can conclude that this does not
provide the required SNR (7 dB) at the fringe of the coverage area if
the desired availability exceeds 99%.

Ideally, we would like to estimate the number of radiobeacons required
to provide satisfactory DGPS service to users in CONUS. This of course
would require an engineering/administrative analysis to determine
optimal beacon locations (tempered by relevant legal and practical
considerations). Such an analysis needs to address the fact that beacons
should be located such that they provide the \"best\" service (in terms
of availability, accuracy, and integrity) to the largest population of
users. In the absence of such an analysis, only very crude estimates can
be made. Such estimates, however, are useful to planners as they
indicate potential problem areas which must be considered and allow one
to get at least a loose grip on potential costs.

Signal levels as a function of range from a given radiobeacon may be
predicted using groundwave propagation models developed by ITS. The
signal level depends on the ground conductivity and radiated antenna
power. For the purposes of this study it is assumed that the radiated
power for a 1 kilowatt transmitter is 150 watts. Using the results of
Table H-1, and ITS LF/MF propagation models, the ranges for a single
beacon in the vicinity of various cities as a function of the annual
availability of a 0 or 7 dB SNR are tabulated in Table H-2. An
alternative view of the situation is shown in Figures H-1 and H-2. From
these plots one can find how SNR requirements affect availability or,
more generally, how signal quality will vary with time at various
distances from the transmitter.

The conductivities specified for a given city are estimates based on
conductivities in the region surrounding the city (FCC § 73.190 Figure
R3). The conductivities used are shown (in parenthesis by the city) in
units of mS/m. The calculations indicate that atmospheric noise
dominates range predictions when a high annual availability is desired
(i.e., 99.9%), while ground conductivity becomes more important as the
desired annual availability decreases.

Table H-2. Range of Individual Beacons (in km) Near Various Cities

for 99.9%, 99%, and 95% Annual Availability

+-------------+--------+--------+--------+--------+--------+--------+
|             | SNR \> | SNR \> | SNR \> | SNR \> | SNR \> | SNR \> |
|             | 7      | 0      | 7 99%  | 0 99%  | 7 95%  | 0 95%  |
|             | 99.9%  | 99.9%  | of     | of     | of     | of     |
|             | of the | of the |        |        |        |        |
|             | year   | year   | the    | the    | the    | the    |
|             |        |        | year   | year   | year   | year   |
+-------------+--------+--------+--------+--------+--------+--------+
| Albuquerque | 82     | 148    | 219    | 329    | 391    | 525    |
|             |        |        |        |        |        |        |
| (10 mS/m)   |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Atlanta     | 77     | 127    | 166    | 239    | 259    | 349    |
|             |        |        |        |        |        |        |
| \(4\)       |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Boise       | 166    | 250    | 310    | 418    | 466    | 587    |
|             |        |        |        |        |        |        |
| \(6\)       |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Chicago     | 97     | 166    | 212    | 314    | 344    | 465    |
|             |        |        |        |        |        |        |
| \(8\)       |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Denver      | 82     | 147    | 222    | 332    | 404    | 539    |
|             |        |        |        |        |        |        |
| \(10\)      |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Fargo       | 99     | 181    | 248    | 379    | 463    | 620    |
|             |        |        |        |        |        |        |
| \(18\)      |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Houston     | 94     | 166    | 233    | 346    | 400    | 535    |
|             |        |        |        |        |        |        |
| \(10\)      |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Los Angeles | 196    | 287    | 213    | 307    | 496    | 619    |
|             |        |        |        |        |        |        |
| \(6\)       |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Miami       | 86     | 143    | 187    | 271    | 302    | 403    |
|             |        |        |        |        |        |        |
| \(5\)       |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| New York    | 150    | 214    | 234    | 313    | 313    | 403    |
| City (3)    |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Oklahoma    | 80     | 153    | 235    | 367    | 451    | 612    |
| City (22)   |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Phoenix     | 171    | 270    | 353    | 484    | 537    | 680    |
|             |        |        |        |        |        |        |
| \(10\)      |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Pittsburgh  | 169    | 268    | 268    | 387    | 438    | 575    |
|             |        |        |        |        |        |        |
| \(10\)      |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| San         | 267    | 386    | 462    | 601    | 630    | 777    |
| Francisco   |        |        |        |        |        |        |
| (10)        |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Seattle     | 172    | 240    | 294    | 381    | 414    | 513    |
|             |        |        |        |        |        |        |
| \(3\)       |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+
| Washington  | 128    | 186    | 202    | 276    | 280    | 366    |
| D.C. (3)    |        |        |        |        |        |        |
+-------------+--------+--------+--------+--------+--------+--------+

![](media/image14.png){width="6.227777777777778in" height="3.625in"}

![](media/image15.png){width="6.227777777777778in" height="3.625in"}

One way of predicting the necessary number of radiobeacons (when
atmospheric noise dominates) is to assume:

> 1\) Due to overlap, each beacon has a coverage area of 70% of a
> circle.
>
> 2\) The mountain/central/southeast noise statistics are relevant to
> 66% of the total area of the U.S. --- (0.66×8×10^6^ km^2^ ).

Using these assumptions, a very rough prediction based on Table H-2 is:

> 1\) For 99.9% availability and 7 dB SNR, 66% of CONUS would be covered
> by beacons with a range of roughly 87 km and 34% of CONUS would be
> covered by beacons with a range of roughly 177 km resulting in an
> estimated 354 beacons (for 0 dB only 118 beacons are required).
>
> 2\) For 99% availability and 7 dB SNR, 66 % of CONUS would be covered
> by beacons with a range of roughly 215 km and 34% of CONUS would be
> covered by beacons with a range of roughly 292 km resulting in an
> estimated 65 beacons (for 0 dB only 31 beacons are required).
>
> 3\) For 95% availability and 7 dB SNR, 66% of CONUS would be covered
> by beacons with a range of roughly 325 km and 34% of CONUS would be
> covered by beacons with a range of roughly 402 km resulting in an
> estimated 23 beacons (for 0 dB only 13 beacons are required).

While the estimates provided above may vary significantly from the
results of a detailed analysis, the predictions do show some important
trends, namely that increasing the availability throughout the coverage
area (particularly on the fringe) has a serious impact on the number of
beacons required, and the more beacons, the more the potential for
interference problems. Also, improvements in receiver technology which
lower the required SNR have a significant impact on the coverage. It
would seem that a judicious placement of beacons would be to have them
relatively close to large population centers (i.e., largest number of
users) where availability is greater at the expense of the fringes where
the number of users is expected to be small.

It should be noted that these results are based on the following
assumptions:

> 1\) a 100 bps broadcast.
>
> 2\) an antenna efficiency of 15%.
>
> 3\) the desired availability is annual availability (vs. worst case 6
> hour time block).

The effects resulting from changes in any of these factors can easily be
estimated by shifting the distance curves in Figures H-1 and H-2. For
example, referring to Figure H-1, in Denver, a 3 dB increase in
bandwidth which corresponds to a 200 bps broadcast reduces the range by
18% (7 dB SNR, 99% availability). The noise field strength statistics
during the worst case time block can exceed annual estimates by 10 dB or
more which in Denver reduces the range by 40% (7 dB SNR, 95%
availability). In both cases, the number of beacons required would
increase substantially.

Another important consideration is the effect skywave propagation might
have on the received signal. If the skywave and the ground wave have
approximately equal amplitudes, then one might easily observe a classic
example of multipath fading in which the signal strength varies between
wide limits. In such a situation, the signal from a radiobeacon would
probably be unreadable. During the daytime the skywave is heavily
attenuated in the lower part of the ionosphere and one does not expect
to observe it. But during the night the absorbing layer disappears and
the skywave can become important. Figure H-3 shows field strengths for
both the ground wave and the skywave --- the ground wave varies with
ground conductivity but is otherwise fairly constant, while the skywave
varies in time and can only be represented here in statistical form. We
note that over land, the two waves are approximately equal at distances
between 200 and 300 km. It therefore follows that it is probably
inadvisable to expect ranges of more than about 200 or 250 km.

![](media/image16.png){width="6.227777777777778in"
height="3.970138888888889in"}

Essentially, self interference produces an additional limit on the
useful range of a radiobeacon. For example, if 95% availability is
acceptable at the fringe of coverage, the range, based on noise
calculations alone, will exceed 300 km; however, skywave interference
will limit the useful range to say 200-250 km. Assuming a 200 km range
and using the methods described previously, 91 beacons are required to
provide coverage of CONUS which effectively provides a lower bound for
the number of beacons required. Even if 99% availability is acceptable
on the fringes of coverage for each beacon, it appears that skywave
interference would be a limiting factor in many cases. It is interesting
to note that the skywave places a practical limit on the use of
increased power to increase the range (or availability).

It is apparent that the factors described above will have an impact on
the successful extension of the USCG system to cover CONUS. It is
important that planning include a careful analysis of the numbers and
locations of beacons so that users will be provided with the information
they require. Other important issues which should be examined are the
effect of man-made impulsive noise in urban areas and effects of nearby
electrical storms. Ignition noise may have a pronounced effect on the
use of radiobeacon broadcast of DGPS on crowded highways. Data losses
due to nearby electrical storms will likely increase latency and
exacerbate bit synchronization problems which have been recently
reported by Gloeckler (private communication). Beacon placement will
also require that close attention be paid to the issue of skywave
interference from other beacons.

**H.1  References**

\[1\] CCIR XVIth Penary Assembly, *Characteristics and Applications of
Atmospheric Radio Noise Data*, Dubrovnik, 1986.

\[2\] P.K. Enge and K.E. Olson, \"Medium Frequency Broadcast of
Differential GPS,\" *IEEE Transactions on Aerospace and Electronic
Systems*, Vol. 26, No.4, July 1990.

\[3\] T.A. Schonhoff, \"A Differential GPS Receiver System Using
Atmospheric Noise Mitigation Techniques,\" in *Proc. Institute of
Navigation (ION) GPS \'91*, Albuquerque, NM, Sept. 1991.

\[4\] U.S. Coast Guard, U.S. Department of Transportation, *Broadcast
Standard for the USCG DGPS Navigation Service, COMDTINST M16577.1*,
Washington, DC, April 1993.

**APPENDIX I**

**CAPABILITIES TABLE VALUES**

This appendix is provided in support of Table 4-1, \"Capabilities
Table,\" and provides the rationale for the assignments of system
capabilities.

**I.1  USCG LF/MF Radiobeacon System**

**Coverage Area, Nationwide:**  No --- the Coast Guard System has been
designed and is currently planned for installation as primarily a
coastal system. Coverage will also include Midwestern rivers and the
Great Lakes. Analysis shows that this system covers approximately 30% of
the contiguous land area of CONUS and the coastal regions of Alaska,
Hawaii, and the U.S. protectorates and territories.

**Coverage Area, Ocean:**  No --- this system does not provide augmented
coverage in the ocean.

**Coverage Area, Coastal:**  Yes --- this system is designed to provide
coverage in coastal areas of the United States and protectorates and
territories. Radiobeacons have a maximum range of approximately 250
nautical miles. This implies by definition that the system also covers
harbor and harbor approach areas of the country.

**Coverage Area, NAS:**  No --- this system is not designed to provide a
specified capability throughout the National Airspace System.

**Availability:**  The USCG reports that the beacon system currently
achieves 99.97% availability.

**Failure Notification Time:**  Based upon the RTCM format, Type 9
messages, and the data rate of 200 bps, failure notification time is 4.2
seconds.

**Predictable Accuracy, Horizontal:**  USCG reports that achievable
accuracy for users with \"high end equipment\" within 300 km of the
radiobeacon is better than 3.0 meters.

**Predictable Accuracy, Vertical:**  Data shows that achievable vertical
accuracies are 1.5 times horizontal accuracies. Thus, vertical accuracy
is expected to be 4.5 meters.

**Probability of Accuracy and Integrity:**  Not defined for this system.

**Time Frame of Availability, Initial Operating Capability:**  The USCG
beacon system will be fully installed in 1995. A number of beacons will
be installed in 1994. The time frame for availability is, therefore,
1994.

**I.2  USCG Expanded LF/MF Radiobeacon System**

**Coverage Area, Nationwide:**  Yes --- the USCG System can be expanded
to provide nationwide coverage with the addition of between 20 to 50
stations.

**Time Frame of Availability, Initial Operating
Capability:**  Nationwide deployment of USCG beacons could begin in 1997
and be completed by 1998. The Time Frame for Availability is therefore
1997.

All other capabilities are identical to System I.1 above.

**I.3  FM Subcarrier System**

**Coverage Area, Nationwide:**  Yes --- these systems can provide
nationwide coverage with an adequate number of FM stations under
contract. The owners/managers do intend to provide nationwide coverage.
It should be understood that FM subcarrier systems provide limited
coverage in mountainous areas where terrain shadowing can impact
coverage.

**Coverage Area, Ocean:**  No --- this system is not designed or
intended to provide coverage in ocean areas. Many FM stations
incorporate directional antennas to avoid coverage in areas of low
population density such as oceans.

**Coverage Area, Coastal:**  No --- this system is not designed or
intended to provide coverage in coastal areas (as defined in the FRP).
FM station coverage has not been demonstrated to cover coastal and
harbor/harbor approach areas of the country with any consistency.

**Coverage Area, NAS:**  No --- this system is not designed to provide a
specified capability in the National Airspace System. It may be capable
of doing so with additional stations, but there is no intention to do so
at this time. FM stations generally design their antennas so as not to
waste energy in the direction above the horizon.

**Availability:**  These systems contract with well established, full
service, FM broadcast stations. Availability then concerns the
maintenance schedule or the failure of these stations, the reference
stations, and the various data links involved. The broadcast stations
used are those that operate 24 hours a day and have redundant equipment
including backup power/generators and alternate transmitters in which
case scheduled maintenance does not in general result in an outage.

The National Association of Broadcasters does not have statistics
regarding FM station availability, however, they believe that most
stations do much better than a one hour outage per year (99.988%). FM
stations have a strong financial incentive to remain up and many
stations are on the air continuously for years. A conservative estimate
would have the system down for one day every 10 years, resulting in an
availability of 99.97%.

**Failure Notification Time:**  Message data comprises an update for a
single satellite, and therefore may be very short. These updates are
assembled at the user\'s receiver and passed on in an RTCM message. Type
1 messages can be supplied every 3 seconds depending upon the amount of
data sharing the subcarrier with DGPS. Thus the time to alarm should be
within 3 seconds but can be much less.

**Predictable Accuracy, Horizontal:**  Industry reports that given the
correct GPS receiver, constellation and environment, FM systems provide
horizontal accuracy in the range of 1 meter 95% of the time. The value
of 1 meter is assigned.

**Predictable Accuracy, Vertical:**  1.5 meters is assumed if horizontal
accuracy of 1 meter is achievable.

**Probability of Accuracy and Integrity:**  Not defined for this system.

**Time Frame of Availability, Initial Operating Capability:**  FM
subcarrier systems are currently operating and therefore have a time
frame of availability of 1994.

**I.4 WAS-1 (WAAS for Integrity, Availability and Accuracy; LADGPS
Systems for Category II/III Approach)**

**Coverage Area, Nationwide:**  Yes --- this system will provide
nationwide augmented coverage. It should be understood that
geosynchronous satellite-based systems provide limited coverage in
mountainous areas or urban canyons where terrain shadowing can impact
coverage. This is particularly true in high latitudes.

**Coverage Area, Ocean:**  Yes --- this system is designed and intended
for use in ocean en route navigation.

**Coverage Area, Coastal:**  No --- geosynchronous satellites will not
cover all coastal areas due to terrain shadowing. There are many coastal
and harbor areas that will be covered by the geosynchronous WAAS system,
however, no geostationary satellite system can ensure complete coastal
coverage.

**Coverage Area, NAS:**  Yes --- this system is designed and intended
for use throughout the National Airspace System.

**Availability:**  This system is specified to provide 99.999 percent
availability.

**Failure Notification Time:**  This system is specified to provide a 2
second failure notification time.

**Predictable Accuracy, Horizontal:**  This system is specified to meet
FAA requirements for all phases of flight. The WAAS portion is specified
to provide an accuracy of 7.6 meters nationwide. The LADGPS portion will
be specified to provide an accuracy of 4.1 meters, depending upon the
type of precision approach.

**Predictable Accuracy, Vertical:**  This system is specified to meet
FAA requirements for all phases of flight. The WAAS portion is specified
to provide an accuracy of 7.6 meters nationwide. The LADGPS portion will
be specified to provide an accuracy of 0.6 meters, depending upon the
type of precision approach.

**Probability of Accuracy and Integrity:**  This system is specified to
provide a probability of accuracy and integrity of 1 x 10^-8^ failures
per hour during Category III approaches as defined in FAA requirements.

**Time Frame of Availability, Initial Operating Capability:**  This
system is specified to have a time frame of availability of 1997.

**I.5 WAS-2 (WAAS for Integrity and Availability; LADGPS Systems for All
Accuracy Requirements for Category I/II/III Approaches)**

**Coverage Area, Nationwide**:  No --- this system will provide
integrity and availability augmentation only. Accuracy augmentation will
not be provided nationwide. LADGPS systems will provide coverage only in
areas around the LADGPS stations.

**Time Frame of Availability, Initial Operating Capability:**  This
system is specified to have a time frame of availability of 1997,
although more time will be required to install additional LADGPS
stations for Category I precision approach requirements.

All other capabilities are identical to System I.4 above.

**I.6 WAS-3 (WAAS for Integrity and Availability, Frequency Other Than
L1; LADGPS Systems for all accuracy requirements for Category II/III
approaches)**

**Time Frame of Availability, Initial Operating Capability:**  This
system is a conceptual system only. It could not be implemented sooner
than 1999.

All other capabilities are identical to System I.4 above.

**I.7  WAS-4 (Encrypted Data Link System)**

**Time Frame of Availability, Initial Operating Capability:**  This
system is a conceptual system only. It could not be implemented sooner
than 1999.

All other capabilities are identical to System I.4 above.

**I.8  WAS-5 (Private GEO Satellite System)**

**Coverage Area, Nationwide:**  Yes --- this system will provide
nationwide augmented coverage. It should be understood that
geosynchronous satellite-based systems provide limited coverage in
mountainous areas or urban canyons where terrain shadowing can impact
coverage. This is particularly true in high latitudes.

**Coverage Area, Ocean:**  Yes --- this system is capable of providing
ocean coverage.

**Coverage Area, Coastal:**  No --- Geosynchronous satellites will not
cover all coastal areas due to terrain shadowing. There are many coastal
and harbor areas that will be covered by geosynchronous systems,
however, no geostationary satellite system can ensure complete coastal
coverage.

**Coverage Area, NAS:**  Yes --- this system is capable of providing
coverage in the National Airspace System, but is not intended for use as
a navigation system.

**Availability:**  Private systems of this type have been in operation
for several years and have demonstrated an availability of up to 99.99
percent.

**Failure Notification Time:**  These systems are capable of providing a
2 second time to alarm depending upon system implementation
characteristics.

**Predictable Accuracy, Horizontal:**  These systems are capable of
providing a horizontal accuracy of 0.6 m (2 drms).

**Predictable Accuracy, Vertical:**  Data shows that achievable vertical
accuracies are 1.5 times horizontal accuracies. Therefore, these systems
can provide 1.0 meter vertical accuracy based upon a horizontal accuracy
of 0.6 meter.

**Probability of Accuracy and Integrity:**  Not defined for this system.

**Time Frame of Availability, Initial Operating Capability:**  These
systems are currently in operation. Therefore, their time frame of
availability is 1994.

**I.9  WAS-6 (Private LEO Systems)**

**Coverage Area, Nationwide:**  Yes --- this system will provide
nationwide augmented coverage. It should be understood that low earth
orbit satellite-based systems are not subject to the same coverage
limitations as geosynchronous systems.

**Coverage Area, Ocean:**  Yes --- this system can provide ocean
coverage.

**Coverage Area, Coastal:**  Yes --- LEO satellites can cover all
coastal areas.

**Coverage Area, NAS:**  Yes --- this type of system can provide
coverage throughout the National Airspace System, but is not intended
for use as a navigation system.

**Availability:**  Analyses have shown that with a sufficient number of
satellites, an availability of 99.999 percent can be achieved.

**Failure Notification Time:**  Potential system providers have
indicated that a 6 second time to alarm is achievable.

**Predictable Accuracy, Horizontal:**  Potential system providers have
indicated that 1 meter accuracy will be possible with this system.

**Predictable Accuracy, Vertical:**  Potential system providers have
indicated that 3 meter vertical accuracy will be possible with this
system.

**Probability of Accuracy and Integrity:**  Not defined for this system.

**Time Frame of Availability, Initial Operating Capability:**  This type
of system will not be available before 1999.

**I.10  Continuously Operating Reference Station (CORS) System**

This system is intended to meet post-processing requirements for survey
and other applications and to provide a cost effective means of
developing and maintaining a national spacial reference system.

**Coverage Area, Nationwide:**  Yes --- this system will be designed to
provide a nationwide post- processing capability.

**Coverage Area, Ocean:**  No --- this system will not provide oceanic
augmented coverage.

**Coverage Area, Coastal:**  No --- CORS does not meet any real time
augmentation requirement. Post-processing coastal requirements would be
met by CORS.

**Coverage Area, NAS:**  No --- this system is not planned to provide
service in the National Airspace System since it is not a real time
system.

**Availability:**  CORS stations will be designed to provide better than
99.0 percent availability. A greater availability is possible but not
planned at this time.

**Failure Notification Time:**  Only real time systems define Failure
Notification Time.

**Predictable Accuracy, Horizontal:**  This system will provide 1
centimeter accuracy to survey users. The accuracy is not provided in
real time.

**Predictable Accuracy, Vertical:**  This system will provide 1
centimeter accuracy to survey users. The accuracy is not provided in
real time.

**Probability of Accuracy and Integrity:**  Not defined for this system.

**Time Frame of Availability, Initial Operating Capability:**  Some CORS
sites are currently operational. Therefore, the time frame of
availability is 1994.

**I.11  Loran-C System**

**Coverage Area, Nationwide:**  Yes --- this system could provide
nationwide augmented coverage.

**Coverage Area, Ocean:**  No --- this system could not provide complete
oceanic augmented coverage.

**Coverage Area, Coastal:**  Yes --- Loran-C could provide augmented
coverage for all coastal areas.

**Coverage Area, NAS:**  No --- this system could not provide augmented
coverage throughout the National Airspace System since the coverage does
not include a portion of the NAS which extends over the ocean.

**Availability:**  The availability of Loran-C is 99.9%.

**Failure Notification Time:**  Using an asynchronous message structure,
a failure notification time of 2 seconds is possible.

**Predictable Accuracy, Horizontal:**  Using Loran-C as a data link to
carry DGPS messages and re-calibrating the Loran-C system can provide
accuracies of 5 meters.

**Predictable Accuracy, Vertical:**  7.5 meters is assumed if horizontal
accuracy of 5.0 meters is achievable.

**Time Frame of Availability, Initial Operating Capability:**  A Loran-C
augmentation could not be available before 1999.

**APPENDIX J**

**DEVELOPMENT OF THE WEIGHTED**

**ANALYTICAL DECISION MATRIX**

The weighted analytical decision matrix was developed for use as a tool
that would assist in determining the final recommendations of this
study. The matrix serves as a guide in evaluating the augmented GPS
architectures that were considered, and does not provide an absolute
solution to determining the most capable augmented GPS architecture.

**J.1 Matrix Organization**

The decision matrix consists of two stages. The first stage contains
spreadsheets that provide a method of organizing and presenting the
large amount of data collected for user requirements and augmented GPS
system performance specifications. This stage is where the Technical
Capabilities Evaluation is performed. The second stage is the Weighted
Analytical Decision Matrix that is used to apply weights to each
evaluation factor and arrive at a weighted score for each architecture
evaluated.

**J.2 Technical Capabilities Evaluation**

Under subtask one of this study, a Federal workshop was conducted which
developed a list of user requirements. Some of these requirements were
removed from further consideration because the suppliers of systems did
not provide performance specifications in terms of these requirements.
Other requirements were not included because performance specifications
were common to all systems and therefore did not provide discrimination
between systems. The remaining requirements provided the basis for the
capabilities depicted in Table 4-1, entitled \"Augmented GPS System
Capabilities.\"

Tables 4-2 through 4-17, entitled \"Augmented GPS System Evaluation,\"
display the results of comparing requirements to system specifications.
There is a separate table for each mode and phase of operation that was
identified. Each block on these spreadsheets indicates a \"YES\" if the
architecture specification meets or exceeds the required value, and a
\"NO\" if the specification does not meet the requirement. These tables
provide an evaluation of the technical capabilities of each system, for
each mode and phase of operation.

Tables 4-18 through 4-21, entitled \"Augmented GPS System Evaluation
Summary,\" display a summary of the results obtained in the technical
capabilities evaluation for each mode of operation.

Table 4-22, entitled \"Augmented GPS System Mode Summary,\" summarizes
the technical capability evaluation results for all modes of operation.
Any system that receives a \"NO\" indication in the technical
evaluation, indicating that it does not meet a stated requirement, is
[not]{.underline} eliminated from further consideration in the final
stage of evaluation, the Weighted Analytical Decision Matrix. This
technical capabilities evaluation is used as a tool in the selection of
systems for evaluation in the Weighted Analytical Decision Matrix.

**J.3 Weighted Analytical Decision Matrix**

The second stage of the decision matrix is the \"Weighted Analytical
Decision Matrix,\" Table 5-1. This table evaluates the architectures
selected against three important parameters: Performance, Cost, and
Security. Each of these parameters was scored separately. No weights
were assigned to the Performance, Cost, and Security parameters to
obtain a total score for each architecture. The assignment of weights to
these parameters would have required value judgements that were beyond
the scope of this study.

**J.4 Scoring Guidelines**

Through a series of meetings, the study team identified evaluation
factors for each parameter. A scoring scale which ranged between 0 and
100 was developed for each factor. The minimum acceptable level was
scored zero. The maximum useful capability was scored 100. Intermediate
levels were established to provide the evaluator guidance on relative
importance of architecture capabilities.

Ground rules for selecting the evaluation factors were:

> **Quantifiable**.  The factor had to be quantifiable.
>
> **Discrimination**. The factor must provide meaningful discrimination
> between architectures.
>
> **Adequate Data**.  Sufficient data had to be available to permit
> evaluation of the factor.
>
> **Independence**.  To prevent redundant weighing, evaluation factors
> and criteria had to be considered only once.

**J.5 Evaluation Parameters**

The scoring factors identified for each Performance, Cost, and Security
parameter were generated to achieve consistency in scoring. The stated
scoring levels were a consensus of the study team and the Working Group.

**J.6 Performance Factors**

The working group considered a number of factors. Several were discarded
because they did not comply with established ground rules. The remaining
factors that were included as part of the performance evaluation are
described in the following sections.

**J.6.1 Real Time Accuracy**

Real time accuracy includes predictable, repeatable, and relative
accuracy. Predictable accuracy is the accuracy of a radionavigation
system\'s position solution with respect to the charted solution. Both
the position solution and the chart must be based upon the same geodetic
datum. Repeatable accuracy is the accuracy with which a user can return
to a position whose coordinates have been measured at a previous time
with the same navigation system. Relative accuracy is the accuracy with
which a user can measure position relative to that of another user of
the same navigation system at the same time.

Table J-1. Real Time Accuracy Scoring Scale

  -----------------------------------------------------------------------
  **LEVEL**                                                 **SCORING
                                                            SCALE**
  --------------------------------------------------------- -------------
  Deformation analysis 1 mm\*                               100

  Surveyors 1 cm                                            99

  FAA Category III .6 m                                     90

  Railroad 1 m                                              85

  General requirements 3 m                                  80

  General requirements 5 m                                  70

  USCG 10 m                                                 60

  SPS 100 m                                                 0
  -----------------------------------------------------------------------

\*Real Time Accuracy scores are based on 2 drms accuracy, at 95%
confidence level.

**J.6.2  Integrity (Time to Alarm)**

Integrity is the ability of a system to provide timely warnings to users
when the system should not be used for navigation. Each architecture\'s
integrity was determined considering methods of integrity determination,
system dynamics, data latency, data update rate, failure notification
time, and criteria for rejection of specific satellite correction data.

Table J-2.  Integrity (Time to Alarm) Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  2 seconds notification time                               100

  6 seconds notification time                               80

  10 seconds notification time                              0
  --------------------------------------------------------- -------------

**J.6.3  Time Frame of Availability, Initial Operating Capability
(IOC)**

These scores were determined with the assumption that 1996 was the
earliest that IOC could be obtained, and 1998 was the latest acceptable
IOC. IOC is defined as when the architecture is sufficiently deployed to
permit beneficial use.

Table J-3.  Time Frame of Availability (IOC) Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  1996 IOC                                                  100

  1997 IOC                                                  90

  1998 IOC or later                                         0
  --------------------------------------------------------- -------------

**J.6.4 Availability**

Availability is the probability that service, meeting the coverage
constraints, will be available to the user. Availability is reduced when
some portion of the architecture is removed from service for maintenance
or through malfunction.

Table J-4.  Availability Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  100%                                                      100

  99.999%                                                   90

  99.7%                                                     85

  95%                                                       0
  --------------------------------------------------------- -------------

**J.6.5 Coverage**

Coverage is a measure of the geographic area where the augmented GPS
service is available assuming the complete architecture is operating
within specification limits. Architecture coverage takes into
consideration signal blockage due to man-made and natural terrain
obstructions as well as meteorological and man-made electrical noise.

Table J-5.  Coverage Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  Worldwide coverage, total                                 100

  Minimum+ Continental U.S. + U.S. territories, Hawaii,     90
  Alaska                                                    

  Minimum+ Continental U.S. (all roads), adjacent waters,   75
  ground up                                                 

  Minimum: All major interstates, U.S. highways and state   0
  routes, all cities, all U.S.-controlled airspace, all     
  harbors and harbor approaches, all inland waterways       
  --------------------------------------------------------- -------------

**J.6.6 International Compatibility**

Internationally compatibility is a measure of the ability of an
architecture to conform to international standards and the ease with
which it can be incorporated into a seamless worldwide infrastructure.

Table J-6. International Compatibility Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  Conforms to international standards                       100

  Does not conform or conflicts with international          80
  standards                                                 

  Major technical obstacle                                  0
  --------------------------------------------------------- -------------

**J.7 Cost Factors**

The cost parameters considered infrastructure cost and user equipment
cost.

**J.7.1 Infrastructure Cost**

Infrastructure cost included initial acquisition cost and a 20 year life
cycle cost expressed in 1994 dollars. A score of 100 is defined as being
a architecture with zero cost to the Federal Government. The highest
cost architecture receives a 0 score. The other architectures are scored
as a percentage of this scale.

Table J-7.  Infrastructure Cost Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  Zero Cost                                                 100

  Highest Cost Architecture                                 0
  --------------------------------------------------------- -------------

**J.7.2 User Equipment Cost**

User equipment costs were estimated considering current cost and
excursions from this cost due to architectural variations. A score of
100 is defined as being a architecture with zero cost. The highest cost
architecture receives a 0 score. The other architectures are scored as a
percentage of this scale.

Table J-8.  User Equipment Cost Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  Zero Cost                                                 100

  Highest Cost Architecture                                 0
  --------------------------------------------------------- -------------

**J.8 Security Factors**

The two major National security concerns are susceptibility to
exploitation and deniability. An additional user concern is
susceptibility to disruption through jamming and spoofing.

**J.8.1 Susceptibility to Exploitation**

Susceptibility to exploitation is a measure of the desirability and cost
for a hostile user to exploit a U.S. provided AGPS service. The
following susceptibility factors were examined:

> **Accuracy**. All viable AGPS architectures are expected to contain a
> differential GPS (DGPS) component providing levels of accuracy having
> hostile utility. Furthermore, civil users require as high accuracy
> DGPS service as can be economically supported. The trend is to provide
> more accurate performance. It was felt that accuracy doesn\'t provide
> significant discrimination for security.
>
> **Update Rate**. The update rate affects DGPS accuracy, response time,
> and warning time. DGPS architectures, which meet civil requirements,
> will provide update rates having hostile utility. While differences in
> update rates can be qualified, no significant discrimination factors
> for security were identified.

**Cost, Size, & Complexity**. An architecture which is too expensive.
too large, or difficult to integrate may have limited hostile utility.
However, the civil thrust is towards low cost, small size and easy
integration. The history of GPS technology indicates cost, size and
integration complexity will reduce over time. It is felt that AGPS user
equipment meeting civil needs will be affordable for hostile use. With
the expected technology growth, cost discrimination criteria for
security couldn\'t be accurately projected.

**Temporal Restrictions**. An architecture which is available only part
of the time may have less hostile utility than one available full time.
Civil navigation requires coverage 24 hours per day. Therefore, it was
felt that there would be no temporal discrimination between viable AGPS
architectures.

**Applicant Screening**. If access to the architecture could be
restricted to friendly users, it would be less subject to hostile
exploitation. However, it may be required that anyone legitimately
operating in U.S. airspace or waters use the AGPS, regardless of our
political relationships. Political relationships change over time.
Discriminating evaluation criteria for applicant screening were not
identified. The converse of applicant screening is covered in the
\"Access Control\" evaluation factor for \"Deniability.\"

**Geographic Restrictions**. An architecture which has limited
geographic coverage is less subject to hostile exploitation. The trend
is expected to be towards greater coverage. Near global coverage, by
AGPS architectures meeting international standards, is likely to evolve,
even though the architectures probably will be operated by different
service providers. Also, geographic restrictions are considered in the
\"Access Control\" evaluation factor for \"Deniability.\" Because of
likely global application of the selected AGPS architecture and to
prevent double weighing, a \"Geographic Restrictions\" evaluation factor
was not included for \"Susceptibility to Exploitation.\"

Even though a number of evaluation factors were identified for
\"Susceptibility to Exploitation,\" none were retained for the decision
matrix. Either they didn\'t provide significant discrimination between
competing architectures or equivalents were covered under
\"Deniability.\"

**J.8.2 Susceptibility to Disruption**

From a user\'s perspective, the AGPS service should have a high immunity
to disruption from jamming, spoofing, atmospheric interference, and
radio frequency interference (RFI). These characteristics should be
addressed in the evaluation of the AGPS service data links. Depending on
AGPS architecture implementation, user desires for resistance to jamming
and spoofing may be inverse deniability requirements. This factor was
not retained for the decision matrix.

**J.8.3 Deniability**

Evaluation of the characteristics of the architecture that affect the
potential to deny access, including signal structure, message content,
transmission frequency, and the area coverage of DGPS transmissions.
Evaluation of any features provided by the architecture to deny access.

The factors defined below were retained for the decision matrix.

**J.8.3.1 Access Control**

Access control is the technical capability to deny use of the AGPS
architecture to hostile users. A architecture which does not permit
denial of access is unacceptable. Architectures which allow denial to be
pinpointed to specific hostile users are rated higher than those which
negatively impact groups of friendly users.

Table J-9.  Access Control Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  Deny by individual subscriber                             100

  Deny by subscriber group                                  80

  Deny by geographic area                                   50

  Turn off entire system                                    0
  --------------------------------------------------------- -------------

**J.8.3.2 Level of Influence**

The level of influence is a measure of the political and managerial
control the U.S. has over denying use of the AGPS architecture. It is
assumed the selected AGPS architecture will proliferate globally. This
will be considered under the \"International Acceptability\" factor
elsewhere in the decision matrix. Unimpeded U.S. control is the most
desirable from a security viewpoint. Even though no U.S. control of a
globally used AGPS architecture is not acceptable to some, the political
reality is that the U.S. may not have control of some portion of a
globally implemented AGPS architecture. Therefore, the minimal
acceptable level was established at \"No U.S. Control.\"

Table J-10.  Level of Influence Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  Total U.S. control                                        100

  Shared control with friendly nations                      80

  Shared control with both friendly and unfriendly nations  10

  No U.S. control                                           0
  --------------------------------------------------------- -------------

**J.8.3.3 Interdiction**

Should the U.S. military be required to engage hostile forces in
regional conflict, any DGPS operating as a threat is assumed to be
operated by the adversary and contained within the region. Interdiction
by U.S. and allied military forces would be to deny adversary military
advantage of precise positioning capability within the region.

Table J-11.  Interdiction Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  Interdictable, no impact on friendly use of architecture  100
  or other valued services by authorized users              

  Interdictable, but impacts other valued services          30

  Interdictable, but interferes with authorized users       0
  --------------------------------------------------------- -------------

**J.8.3.4 Post-Decision Response Time**

Post-decision response time is the time required to implement denial
once the decision to deny access to the AGPS service has been made by
the appropriate authority. If denial activation is delayed, hostile
users may have use of the AGPS service for a militarily significant
period of time.

Table J-12.  Post-Decision Response Time Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  Seconds                                                   100

  Minutes                                                   95

  Hours                                                     80

  Days                                                      0
  --------------------------------------------------------- -------------

**J.8.3.5 Jammability**

Jammability is a measure of the ease of denying use of the AGPS service
and impact on other desirable services using jamming. Jamming is a
technique available to deny use of the AGPS service when the U.S. level
of influence and/or the technical access control features are inadequate
to provide security. The evaluation criteria address jamming from the
perspective of preventing hostile use of the AGPS architecture. The
desire is to be able to use jamming to prevent hostile use without
disrupting friendly use of the AGPS architecture or other services in
the same frequency band. Having the capability to deny use of the AGPS
architecture using jamming may conflict with users desires to minimize
the possibility of service disruption by intentional or unintentional
jamming.

Table J-13.  Jammability Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  Jammable, no impact on friendly use of architecture or    100
  other valued services by authorized users                 

  Jammable, but impacts other valued services               30

  Jammable, but interferes with authorized users            5

  Cannot be jammed                                          0
  --------------------------------------------------------- -------------

**J.8.3.6 Vulnerability of Denial**

Vulnerability of the denial capability is an assessment of how easily
the access control features of the AGPS architecture can be
circumvented. If access control can be easily circumvented, it is almost
the same as having no access control. No redundancy or security of
access control features is unacceptable.

Table J-14.  Vulnerability of Denial Scores

  --------------------------------------------------------- -------------
  **CHARACTERISTIC**                                        **SCORE**

  Secure facilities and data links on U.S. soil             100

  Encrypted data links or secure facilities                 50

  Redundant, but unsecured command and control facilities   0
  and data links                                            
  --------------------------------------------------------- -------------

**J.9 Factor Weighting**

The study team and Working Group assigned weights to the factors
associated with each parameter. Factor weights were determined by the
application of two decision analysis guidelines: "swing weights" and
"additive weights.\" "Swing weights" reflect the relative importance of
the difference between scores of 0 and 100 on one factor as compared
with 0 to 100 on each of the other factors. "Additive weights" reflect
the fact that the weights are on a ratio scale; a single factor with a
weight of 100 is equally important as the sum of any two other factors
that each have weights of 50.

**J.10 Scoring**

The study team and Working Group assigned scores to each architecture
for all the factors included in the decision matrix. The assigned scores
were based upon the scoring scales described above and reflected the
collective subjective judgment of the study team and working group.

Factor scores for each architecture were then multiplied by the relative
importance weights assigned to the respective factor to arrive at a
weighted score. Individual weighted scores for each factor contained
within each parameter were summed to provide an aggregate score for that
parameter for each architecture.

**APPENDIX K**

**ARCHITECTURE EVALUATION**

This appendix is provided in support of Tables 5-1, 5-2, and 5-3, and
provides the rationale for the assignments of architecture scores.

**K.1 ARCHITECTURE 1 --- USCG system deployed as currently planned,
WAS-1 (FAA WAAS for integrity, availability, and accuracy; LADGPS
systems for Category II/III precision approach requirements), all
stations compliant with CORS standard.**

**K.1.1 Performance Factor Scores**

**Accuracy: 80.**  The accuracy of this architecture is based upon
extensive testing by USCG and independent test results by USACE, NOAA
and others. Based on the testing that has been performed, the accuracy
of the system is 3 meters 2 drms within the coverage area (based on the
USCG system). Because this accuracy dominates, the architecture receives
a score of 80.

**Integrity (Time to Alarm): 100.**  The time to alarm for the USCG
system is 4.2 seconds, the time to alarm for the WAAS is 6 seconds, and
the time to alarm for the LADGPS portion of the FAA system is 2 seconds.
This meets all user requirements for time to alarm and receives a 100
score.

**Availability: 90.**  This system will meet FAA availability
requirements (99.999%) as well as all other user requirements for
availability except the railroad control requirement of 100% in the
coverage region.

**Time Frame of Availability, Initial Operating Capability: 95.**  IOC
for the USCG system will be December, 1995. The WAS-1 portion of the
architecture has an IOC of 1997.

**Coverage: 0.**  This system does not meet the minimum requirements as
specified. The minimum requirements are all major interstates, U.S.
highways and state routes, all cities, all U.S. controlled air space,
all harbors and harbor approaches, and all inland waterways. The USCG
system does not provide inland coverage and the WAS-1 system does not
provide coverage in higher latitudes and many harbor and harbor
approaches or inland waterways.

**International Compatibility: 95.** The USCG system conforms to
International Telecommunication Union (ITU) Standard 823, \"Recommended
Standard for Maritime Differential Global Navigation Satellite
Systems.\"

At the present time, there are no international aviation standards for
augmented GPS. Ongoing discussions within the international aviation
community indicate that the WAAS, as currently specified by FAA, will be
accepted internationally. Various nations throughout the world are
currently experimenting with LADGPS systems to support precision
approach and landing. There is also reason to expect, therefore, that
LADGPS systems as ultimately specified and adopted by FAA will also be
accepted internationally.

The score is 95 since it can be said that this system would meet or
likely meet international standards when they are developed.

**K.1.2 Cost Factor Scores**

**Infrastructure Cost: 24.**[^5]  The 20 year life cycle cost for the
existing USCG system of 61 stations will be: \$14.2M +20(\$4.2M) =
\$98.2M.

The cost of 61 USCG CORS-compliant sites is estimated at \$0.6M. The FAA
WAAS sites are already specified to be CORS-compliant and require no
additional funding. The cost to establish the central facility is
\$1.0M. Thus, the total CORS system will cost an estimated \$1.6M.

The WAAS life cycle cost is estimated to be on the order of \$1,139M.
The LADGPS systems life cycle cost is estimated to be on the order of
\$195M. These costs include the cost of airport lighting and procedures
for use of the WAAS and LADGPS systems within the NAS. The total life
cycle cost of this portion of the architecture, therefore, is estimated
at approximately \$1,334M.

The total life cycle cost of this architecture is estimated to be:

\$98.2M + \$1.6M + \$1,334M = \$1,433.8M.

Therefore, the infrastructure cost score for this architecture is 20.

**User Equipment Cost: 14.**[^6]  Marine user equipment costs range from
\$2,000 for general marine equipment to \$22,500 for high precision
on-the-fly kinematic navigation.

Aviation user equipment costs range from \$4,000 for general aviation
equipment to \$90,000 for more sophisticated commercial aircraft.

Land user equipment costs range from \$500 for recreational user
equipment to \$22,500 for high precision geodetic survey equipment.

The maximum total user cost for this architecture is estimated to be:

\$22,500 + \$90,000 + \$22,500 = \$135,000.

Therefore, the user equipment cost score for this architecture is 14.

**K.1.3 Security Factor Scores**

If adopted by the U.S. and replicated worldwide, this architecture would
present a potential threat to U.S. and allied forces in combat areas.
Precise position, time, and velocity data transmitted on the GPS Ll
frequency from geosynchronous satellites could provide military utility.
It negates selective availability, the basic GPS security protection;
impairs U.S. efforts to restrict the export of precise guidance systems;
and limits countermeasure efforts. The countermeasures that are
available could disrupt the peaceful use of GPS on a worldwide basis or
at the least on a near-hemispheric basis.

**Access Control: 0.**  The WAAS differential broadcast coverage from a
geosynchronous satellite is nearly hemispheric. Should the U.S. be
required to deny GPS augmentation within a particular region covered by
the WAAS, the WAAS must be turned off. In effect, this may not be a
realistic option since significantly more non­-combatants than combatants
would be denied service.

**Level of Influence: 80.**  It is assumed that in a seamless WAAS
architecture, some level of U.S. control would be maintained as a result
of U.S. technology transfer and required configuration control. In
addition, nations with the economic infrastructure capable of sustaining
a WAAS are assumed to be friendly to U.S. interests.

**Interdictability: 0.**  It is assumed that future U.S. military
conflicts will be limited to a region. Any WAAS operation considered a
threat is assumed to be operated by another country outside the region
and not involved with hostilities. Therefore, military interdiction of
the WAAS is not considered as a viable option.

**Post-Decision Response Time: 80.**  If the DGPS control station is in
a country cooperative to the U.S. and the decision is made to exercise
access control, it could require hours to identify and select
appropriate transmission sites, coordinate operations, and terminate
service.

**Jammability: 5.**  The designated RF downlink for the WAAS is L1.
Jamming of the WAAS L1 will also jam the GPS Ll, thereby jamming all GPS
users within the vicinity.

**Vulnerability of Denial: 50.**  It is assumed that WAAS and DGPS
stations would be operated and maintained within secure facilities.

**K.2 ARCHITECTURE 2 --- USCG(E) system deployed nationwide, WAS-1 (FAA
WAAS for integrity, availability, accuracy; LADGPS systems for Category
II/III precision approach requirements), all stations compliant with the
CORS standard.**

**K.2.1 Performance Factor Scores**

**Accuracy: 80.**  The accuracy of this architecture is based upon
extensive testing by USCG and independent test results by USACE, NOAA
and others. Based on the testing that has been performed, the accuracy
of the system is 3 meters 2 drms within the coverage area (based on the
USCG system). This accuracy dominates and the architecture receives a
score of 80.

**Integrity (Time to Alarm): 100.**  The time to alarm for the USCG
system is 4.2 seconds, the time to alarm for the WAAS is 6 seconds, and
the time to alarm for the LADGPS portion of the FAA system is 2 seconds.
All user requirements are met, therefore this architecture receives a
score of 100.

**Availability: 90.**  This system will meet FAA availability
requirements (99.999%) as well as all other user requirements for
availability except the railroad control requirement of 100% in the
coverage region. It therefore receives a score of 90.

**Time Frame of Availability, Initial Operating Capability: 90.**  IOC
for the USCG(E) system could be December, 1997. The WAS-1 portion of the
architecture also has an IOC of 1997. The architecture therefore
receives a score of 90.

**Coverage: 90.**  The USCG(E) portion of this architecture provides
coverage for all major interstates, all highways and state routes, all
cities, all harbor and harbor approaches and inland waterways in the
U.S. and its territories. The WAS-1 portion of this architecture
provides coverage for the NAS. Therefore this architecture receives a
score of 90.

**International Compatibility: 95.** The USCG(E) system conforms to
International Telecommunication Union (ITU) Standard 823, \"Recommended
Standard for Maritime Differential Global Navigation Satellite
Systems.\"

At the present time, there are no international aviation standards for
augmented GPS. Ongoing discussions within the international aviation
community indicate that the WAAS, as currently specified by FAA will be
accepted internationally. Various nations throughout the world are
currently experimenting with LADGPS systems to support precision
approach and landing. There is also reason to expect, therefore, that
LADGPS systems as ultimately specified and adopted by FAA will also be
accepted internationally.

The score is 95 since it can be said that this system would meet or
likely meet international standards when they are developed.

**K.2.2 Cost Factor Scores**

**Infrastructure Cost: 23.**  The total life cycle cost over 20 years
for the existing USCG system of 61 stations will be: \$14.2M +20(\$4.2M)
= \$98.2M. The additional 20-50 stations required for CONUS coverage
would cost \$3-8 million. The annual operating cost would be \$1-2
million for the additional stations. The maximum total life cycle cost
over 20 years for the USCG(E) system would be \$146M.

The cost of 110 USCG(E) CORS-compliant sites is estimated at \$1.1M. The
FAA WAAS sites are already specified to be CORS-compliant and require no
additional funding. The cost to establish the central facility is
\$1.0M. Thus, the total nationwide CORS system will cost an estimated
\$2.1M. It is anticipated that the USCG(E) and WAAS sites will provide
adequate coverage.

The WAAS life cycle cost is estimated to be on the order of \$1139M. The
LADGPS systems life cycle cost is estimated to be on the order of
\$195M. These costs include the cost of airport lighting and procedures
for use of the WAAS and LADGPS systems within the NAS. The total life
cycle cost of this portion of the architecture, therefore, is estimated
at approximately \$1,334M.

The total life cycle cost of this architecture is estimated to be:

\$146M + \$2.1M + \$1,334M = \$1,482.1M.

Therefore, the infrastructure cost score for this architecture is 17.

**User Equipment Cost: 14.**  Marine user equipment costs range from
\$2,000 for general marine equipment to \$22,500 for high precision
on-the-fly kinematic navigation.

Aviation user equipment costs range from \$4,000 for general aviation
equipment to \$90,000 for more sophisticated commercial aircraft.

Land user equipment costs range from \$500 for recreational user
equipment to \$22,500 for high precision geodetic survey equipment.

The maximum total user cost for this architecture is estimated to be:

\$22,500 + \$90,000 + \$22,500 = \$135,000.

Therefore, the user equipment cost score for this architecture is 14.

**K.2.3 Security Factor Scores**

If adopted by the U.S. and replicated worldwide, this architecture would
present a potential threat to U.S. and allied forces in combat areas.
Precise position, time, and velocity data transmitted on the GPS L‑l
frequency from geosynchronous satellites could provide military utility.
It negates selective availability, the basic GPS security protection;
impairs U.S. efforts to restrict the export of precise guidance systems;
and limits countermeasure efforts. The countermeasures that are
available could disrupt the peaceful use of GPS on a worldwide basis or
at the least on a hemispheric basis.

**Access Control: 0.**  The WAAS differential broadcast coverage from a
geosynchronous satellite is nearly hemispheric. Should the U.S. be
required to deny GPS augmentation within a particular region covered by
the WAAS, the WAAS must be turned off. In effect, this may not be a
realistic option since significantly more non­-combatants than combatants
would be denied service.

**Level of Influence: 80.**  It is assumed that in a seamless WAAS
architecture, some level of U.S. control would be maintained as a result
of U.S. technology transfer and required configuration control. In
addition, nations with the economic infrastructure capable of sustaining
a WAAS are assumed to be friendly to U.S. interests.

**Interdictability: 0.**  It is assumed that future U.S. military
conflicts will be limited to a region. Any WAAS operation considered a
threat is assumed to be operated by another country outside the region
and not involved with hostilities. Therefore, military interdiction of
the WAAS is not considered as a viable option.

**Post-Decision Response Time: 80.**  If the DGPS control station is in
a country cooperative to the U.S. and the decision is made to exercise
access control, it could require hours to identify and select
appropriate transmission sites, coordinate operations, and terminate
service.

**Jammability: 5.**  The designated RF downlink for the WAAS is L1.
Jamming of the WAAS L1 will also jam the GPS Ll, thereby jamming all GPS
users within the vicinity.

**Vulnerability of Denial: 50.**  It is assumed that WAAS and DGPS
stations would be operated and maintained within secure facilities.

**K.3 ARCHITECTURE 3 --- USCG(E) system deployed nationwide, WAS-2 (WAAS
for integrity and availability only; LADGPS systems for Category
I/II/III precision approach requirements), all stations compliant with
the CORS standard.**

**K.3.1 Performance Factor Scores**

**Accuracy: 80.**  The accuracy of this architecture is based upon
extensive testing by USCG and independent test results by USACE, NOAA
and others. Based on the testing that has been performed, the accuracy
of the system is 3 meters 2 drms within the coverage area (based on the
USCG system). This accuracy dominates and the architecture receives a
score of 80.

**Integrity (Time to Alarm): 100.**  The time to alarm for the USCG
system is 4.2 seconds, the time to alarm for the WAAS is 6 seconds, and
the time to alarm for the LADGPS portion of the FAA system is 2 seconds.
All user requirements are met, therefore this architecture receives a
score of 100.

**Availability: 90.**  This system will meet FAA availability
requirements (99.999%) as well as all other user requirements for
availability except the railroad control requirement of 100% in the
coverage region. It therefore receives a score of 90.

**Time Frame of Availability, Initial Operating Capability: 90.**  IOC
for the USCG(E) system could be December, 1997. The WAS-2 portion of the
architecture also has an IOC of 1997. The architecture therefore
receives a score of 90.

**Coverage: 90.**  The USCG(E) portion of this architecture provides
coverage for all major interstates, all highways and state routes, all
cities, all harbor and harbor approaches and inland waterways in the
U.S. and its territories. The WAS-2 portion of this architecture
provides coverage for the NAS. Therefore this architecture receives a
score of 90.

**International Compatibility: 85.** The USCG(E) system conforms to
International Telecommunication Union (ITU) Standard 823, \"Recommended
Standard for Maritime Differential Global Navigation Satellite
Systems.\"

At the present time, there are no international aviation standards for
augmented GPS. Ongoing discussions within the international aviation
community seem to indicate that the WAAS, as currently specified by FAA
will be accepted internationally. Various nations throughout the world
are currently experimenting with LADGPS systems to support precision
approach and landing. There is also reason to expect, therefore, that
LADGPS systems as ultimately specified and adopted by FAA will also be
accepted internationally. Since the international community does not
appear to share the U.S. reservations concerning the accuracy (Phase II)
component of the WAAS, a U.S. WAAS with only Phase I (integrity and
availability) components may be less acceptable internationally than the
full (Phase I and II) WAAS. The score is, therefore, 85.

**K.3.2 Cost Factor Scores**

**Infrastructure Cost: 17.**  The 20 year life cycle cost for the
existing USCG system of 61 stations will be: \$14.2M +20(\$4.2M) =
\$98.2M. The additional 20-50 stations required for CONUS coverage would
cost \$3-8 million. The annual operating cost would be \$1-2 million for
the additional stations. The maximum total life cycle cost over 20 years
for the USCG(E) system would be \$146M.

The cost of 110 USCG(E) CORS-compliant sites is estimated at \$1.1M. The
FAA WAAS sites are already specified to be CORS-compliant and require no
additional funding. The cost to establish the central facility is
\$1.0M. Thus, the total nationwide CORS system will cost an estimated
\$2.1M. It is anticipated that the USCG(E) and WAAS sites will provide
adequate coverage.

The WAAS component of this architecture will satisfy aviation
requirements for all phases of flight through non-precision approach,
WAAS Phase I as briefed at the TSARC. The WAAS Phase I life cycle cost
is estimated to be on the order of \$670M. Since the WAAS Phase I will
not satisfy Category I requirements, 620 Category I LADGPS systems will
be required under this architecture. The Category I LADGPS systems life
cycle cost is estimated to be on the order of \$560M. The Category
II/III LADGPS systems life cycle cost is estimated to be on the order of
\$195M. The total life cycle cost of this portion of the architecture,
therefore, is estimated at \$1,425M.

The total life cycle cost of this architecture is estimated to be:

\$146M + \$2.1M + \$1,425M = 1,573.1M.

Therefore the infrastructure cost score for this system is 12.

**User Equipment Cost: 8.**  Marine user equipment costs range from
\$2,000 for general marine equipment to \$22,500 for high precision
on-the-fly kinematic navigation.

Aviation user equipment costs range from \$4,400 for general aviation
equipment to \$99,000 for more sophisticated commercial aircraft.

Land user equipment costs range from \$500 for recreational user
equipment to \$22,500 for high precision geodetic survey equipment.

The maximum total user cost for this architecture is estimated to be:

\$22,500 + \$99,000 + \$22,500 = \$144,000.

Therefor, the user equipment cost score for this architecture is 9.

**K.3.3 Security Factor Scores**

The use of a geosynchronous satellite to transmit integrity data and
provide additional ranging is not considered a military threat. As in
other architectures, short range transmitters such as LADGPS stations
used to transmit accuracy corrections can be mitigated by conventional
means.

**Access Control: 50.**  Access control is achieved by terminating
correction transmissions at specified locations. This constitutes access
control by geographic location.

**Level of Influence: 80.**  It is assumed that in a seamless
architecture, some level of U.S. control would be maintained as a result
of U.S. technology transfer and required configuration control. In
addition, nations with the economic infrastructure capable of sustaining
such an architecture are assumed to be friendly to U.S. interests.

**Interdictability: 100.**  It is assumed that future U.S. military
conflicts will be limited to a region. Any DGPS not being operated by
U.S. or allied forces will be deemed hostile. Interdiction by U.S. and
allied forces would negate this threat.

**Post-Decision Response Time: 80.**  If the DGPS control station is in
a country cooperative to the U.S. and the decision is made to exercise
access control, it could require hours to identify and select
appropriate transmission sites, coordinate operations, and terminate
service.

**Jammability: 100.**  It is assumed that DGPS stations will have RF
links which will not interfere with other RF systems, including GPS Ll.
Therefore, jamming the correction portion of the architecture does not
impact friendly use of the overall architecture.

**Vulnerability of Denial: 50.**  It is assumed that WAAS and DGPS
stations would be operated and maintained within secure facilities.

**K.4 ARCHITECTURE 4 --- USCG(E) system deployed nationwide, WAS-3 (WAAS
for integrity and availability, accuracy at a frequency other than L1;
LADGPS systems for Category II/III precision approach requirements), all
stations compliant with CORS standard.**

**K.4.1 Performance Factor Scores**

**Accuracy: 80.**  The accuracy of this architecture is based upon
extensive testing by USCG and independent test results by USACE, NOAA
and others. Based on the testing that has been performed, the accuracy
of the system is 3 meters 2 drms within the coverage area (based on the
USCG system). This accuracy dominates and the architecture receives a
score of 80.

**Integrity (Time to Alarm): 100.**  The time to alarm for the USCG
system is 4.2 seconds, the time to alarm for the WAAS is 6 seconds, and
the time to alarm for the LADGPS portion of the FAA system is 2 seconds.
All user requirements are met, therefore this architecture receives a
score of 100.

**Availability: 90.**  This system will meet FAA availability
requirements (99.999%) as well as all other user requirements for
availability except the railroad control requirement of 100% in the
coverage region. Therefore, it receives a score of 90.

**Time Frame of Availability, Initial Operating Capability: 0.**  This
architecture exists only in conceptual form. Suitable alternative
communications satellites with the capability to provide correction
messages at other than the GPS L1 frequency are not readily available.
The current lack of definition virtually assures that this architecture
could not be operational prior to 1998. Consequently, this architecture
receives a score of 0.

**Coverage: 90.** The USCG(E) portion of this architecture provides
coverage for all major interstates, all highways and state routes, all
cities, all harbor and harbor approaches and inland waterways in the
U.S. and its territories. The WAS-3 portion of this architecture
provides coverage for the NAS. Therefore, this architecture receives a
score of 90.

**International Compatibility: 88.** The USCG system conforms to
International Telecommunication Union (ITU) Standard 823, \"Recommended
Standard for Maritime Differential Global Navigation Satellite
Systems.\"

At the present time, there are no international aviation standards for
augmented GPS. Ongoing discussions within the international aviation
community seem to indicate that the WAAS, as currently specified by FAA
will be accepted internationally. Various nations throughout the world
are currently experimenting with LADGPS systems to support precision
approach and landing. There is also reason to expect, therefore, that
LADGPS systems as ultimately specified and adopted by FAA will also be
accepted internationally. The international community does not appear to
share the U.S. reservations with the accuracy (Phase II) component of
the WAAS. A WAAS providing error corrections on the GPS L1 frequency
permits the use of a relatively simple avionics suite to receive
transmissions from the GPS satellites themselves as well as from the
differential station. Consequently, a U.S. WAAS providing differential
corrections, i.e., accuracy enhancements, at a completely different
frequency will likely be less acceptable internationally than the full
(Phase I and II) WAAS with accuracy corrections at the GPS L1 frequency,
but more acceptable than no accuracy component at all. Therefore, this
architecture receives a score of 88.

**K.4.2 Cost Factor Scores**

**Infrastructure Cost: 23.** The 20 year life cycle cost for the
existing USCG system of 61 stations will be: \$14.2M +20(\$4.2M) =
\$98.2M. The additional 20-50 stations required for CONUS coverage would
cost \$3-8 million. The annual operating cost would be \$1-2 million for
the additional stations. The maximum total life cycle cost over 20 years
for the USCG(E) system would be \$146M.

The cost of 110 USCG(E) CORS-compliant sites is estimated at \$1.1M. The
FAA WAAS sites are already specified to be CORS-compliant and require no
additional funding. The cost to establish the central facility is
\$1.0M. Thus, the total nationwide CORS system will cost an estimated
\$2.1M. It is anticipated that the USCG(E) and WAAS sites will provide
adequate coverage.

The WAAS life cycle cost is estimated to be on the order of \$1139M. The
LADGPS systems life cycle cost is estimated to be on the order of
\$195M. The total life cycle cost of this portion of the architecture,
therefore, is estimated at approximately \$1,334M.

The total life cycle cost of this architecture is estimated to be:

\$146M + \$2.1M + \$1,334M = \$1,482.1M.

Therefore, the infrastructure cost score for this architecture is 17.

**User Equipment Cost: 8.**  Marine user equipment costs range from
\$2,000 for general marine equipment to \$22,500 for high precision
on-the-fly kinematic navigation.

Aviation user equipment costs range from \$4,400 for general aviation
equipment to \$99,000 for more sophisticated commercial aircraft.

Land user equipment costs range from \$500 for recreational user
equipment to \$22,500 for high precision geodetic survey equipment.

The maximum total user cost for this architecture is estimated to be:

\$22,500 + \$99,000 + \$22,500 = \$144,000.

Therefor, the user equipment cost score for this architecture is 9.

**K.4.3 Security Factor Scores**

Transmitted data from geosynchronous satellites on frequencies other
than Ll will permit jamming that does not interfere with friendly GPS
use. The wide availability of the data, however, will increase the
countermeasure requirements. LADGPS stations, which transmit accuracy
corrections, can be mitigated by conventional means.

**Access Control: 0.**  The WAAS differential broadcast coverage from a
geosynchronous satellite is nearly hemispheric. Should the U.S. be
required to deny GPS augmentation within a particular region covered by
the WAAS, the WAAS must be turned off. In effect, this may not be a
realistic option since significantly more non­-combatants than combatants
would be denied service.

**Level of Influence: 80.**  It is assumed that in a seamless WAAS
architecture, some level of U.S. control would be maintained as a result
of U.S. technology transfer and required configuration control. In
addition, nations (or group of nations) with the economic infrastructure
capable of sustaining a WAAS are assumed to be friendly to U.S.
interests.

**Interdictability: 0.**  It is assumed that future U.S. military
conflicts will be limited to a region. Any WAAS operation considered a
threat is assumed to be operated by another country outside the region
and not involved with hostilities. Therefore, military interdiction of
the WAAS is not considered as a viable option.

**Post-Decision Response Time: 80.**  If the DGPS control station is in
a country cooperative to the U.S. and the decision is made to exercise
access control, it could require hours to identify and select
appropriate transmission sites, coordinate operations, and terminate
service.

**Jammability: 30.**  Jamming the differential correction frequency will
likely impact other valued services, but will not preclude the continued
use of integrity and availability capabilities on L1.

**Vulnerability of Denial: 50.**  It is assumed that WAAS and DGPS
stations would be operated and maintained within secure facilities.

**K.5 ARCHITECTURE 5 --- USCG(E) system deployed nationwide, WAS-4 (WAAS
encrypted for integrity, availability, and accuracy; LADGPS systems for
Category II/III precision approach requirements), all stations compliant
with CORS standard.**

**K.5.1 Performance Factor Scores**

**Accuracy: 80.**  The accuracy of this architecture is based upon
extensive testing by USCG and independent test results by USACE, NOAA
and others. Based on the testing that has been performed, the accuracy
of the system is 3 meters 2 drms within the coverage area (based on the
USCG system). This accuracy dominates and the architecture receives a
score of 80.

**Integrity (Time to Alarm): 100.**  The time to alarm for the USCG
system is 4.2 seconds, the time to alarm for the WAAS is 6 seconds, and
the time to alarm for the LADGPS portion of the FAA system is 2 seconds.
All user requirements are met, therefore this architecture receives a
score of 100.

**Availability: 90.**  This system will meet FAA availability
requirements (99.999%) as well as all other user requirements for
availability except the railroad control requirement of 100% in the
coverage region. Therefore, it receives a score of 90.

**Time Frame of Availability, Initial Operating Capability
(IOC): 0.**  IOC for the USCG(E) system could be December, 1997. IOC for
the WAS-4 portion of the architecture has the potential, from a
technical perspective, to meet a 1997 IOC date if the encryption
concepts in this architecture are incorporated into the currently
planned FAA WAAS. However, this would require an engineering change to
the current WAAS specifications. Based on procurement regulations,
funding, and the level of coordination required, it is unlikely that an
IOC date of earlier than 1999 could be achieved. The architecture,
therefore, receives a score of 0.

**Coverage: 90.**  The USCG(E) portion of this architecture provides
coverage for all major interstates, all highways and state routes, all
cities, all harbor and harbor approaches and inland waterways in the
U.S. and its territories. The WAS-4 portion of this architecture
provides coverage for the NAS. Therefore, this architecture receives a
score of 90.

**International Compatibility: 30.** The USCG(E) system conforms to
International Telecommunication Union (ITU) Standard 823, \"Recommended
Standard for Maritime Differential Global Navigation Satellite
Systems.\"

At the present time, there are no international aviation standards for
augmented GPS. Various nations throughout the world are currently
experimenting with LADGPS systems to support precision approach and
landing. There is also reason to expect, therefore, that LADGPS systems
as ultimately specified and adopted by FAA will also be accepted
internationally.

To date there is no precedent in the international community for an
encrypted aviation navigation aid. Therefore, this architecture receives
a score of 30.

**K.5.2 Cost Factor Scores**

**Infrastructure Cost: 0.**  The 20 year life cycle cost for the
existing USCG system of 61 stations will be: \$14.2M +20(\$4.2M) =
\$98.2M. The additional 20-50 stations required for CONUS coverage would
cost \$3-8 million. The annual operating cost would be \$1-2 million for
the additional stations. The maximum total life cycle cost over 20 years
for the USCG(E) system would be \$146M.

The cost of 110 USCG(E) CORS-compliant sites is estimated at \$1.1M. The
FAA WAAS sites are already specified to be CORS-compliant and require no
additional funding. The cost to establish the central facility is
\$1.0M. Thus, the total nationwide CORS system will cost an estimated
\$2.1M. It is anticipated that the USCG(E) and WAAS sites will provide
adequate coverage.

The WAAS life cycle cost is estimated to be on the order of \$1139M. The
estimated cost addition for the WAS-4 system enhancements is \$300M. The
LADGPS systems life cycle cost is estimated to be on the order of
\$195M. The total life cycle cost of this portion of the architecture,
therefore, is estimated at approximately \$1,634M.

The total life cycle cost of this architecture is estimated to be:

\$146M + \$2.1M + \$1,634M = \$1,782.1M.

This makes this architecture the most costly one proposed and it
receives an infrastructure cost score of 0.

**User Equipment Cost: 0.**  Marine user equipment costs range from
\$2,000 for general marine equipment to \$22,500 for high precision
on-the-fly kinematic navigation.

Aviation user equipment costs range from \$5,000 for general aviation
equipment to \$112,500 for more sophisticated commercial aircraft.

Land user equipment costs range from \$500 for recreational user
equipment to \$22,500 for high precision geodetic survey equipment.

The maximum total user cost for this architecture is estimated to be:

\$22,500 + \$112,500 + \$22,500 = \$157,500.

This makes this architecture the most costly one proposed and it
receives a user equipment cost score of 0.

**K.5.3 Security Factor Scores**

The WAAS portion of this architecture is an encrypted version of
Architecture K.2. If adopted by the U.S. and deployed worldwide, this
architecture would help mitigate the potential threats to U.S. and
allied forces in combat areas.

**Access Control: 75.**  Access to the USCG(E) portion of the
architecture would be denied by geographic region. The security factors
of the WAAS portion greatly improve the overall security of the
architecture since access control can be denied by subscriber groups or
possibly even by individual subscriber. The USCG(E) portion of this
architecture is not encrypted, resulting in a score of less than 100.

**Level of Influence: 90.**  It is assumed that the WAAS portion of this
architecture is under U.S. control. However, LADGPS systems could exist
outside direct U.S. control. Therefore, it can not be assumed that the
U.S. would be able to exert influence over the entire architecture.

**Interdictability: 100.**  The U.S. would have no need to interdict a
U.S. controlled system. As in other architectures, short range
transmitters such as LADGPS stations used to transmit accuracy
corrections can be mitigated by conventional means.

**Post-Decision Response Time: 80.**  If the DGPS control station is in
a country cooperative with the U.S. and the decision is made to exercise
access control, it could require hours to identify and select
appropriate transmission sites, coordinate operations, and terminate
service. A similar time would be required for control of the WAAS
portion of the architecture.

**Jammability: 100.**  The WAAS portion of this architecture is under
U.S. control and would not require jamming to deny service. For the
LADGPS portions, it is assumed that they will have RF links which will
not interfere with other RF systems, including GPS Ll. Therefore,
jamming this portion of the architecture does not impact friendly use of
the overall architecture.

**Vulnerability of Denial: 50.**  It is assumed that WAAS and DGPS
stations would be operated and maintained within secure facilities.

[^1]: These authors are with the Institute for Telecommunication
    Sciences, National Telecommunications and Information
    Administration, U.S. Department of Commerce, Boulder, Colorado
    80303.

[^2]: These authors are with the U.S. Army Topographic Engineering
    Center, Alexandria, Virginia 22315.

[^3]: This author is with the Volpe National Transportation Systems
    Center, Research and Special Programs Administration, U.S.
    Department of Transportation, Cambridge, Massachusetts 02142.

[^4]: These authors are with Overlook Systems Technologies, Inc.,
    Vienna, Virginia 22182.

[^5]: 1Infrastructure cost was scaled relative to the most costly
    system. The most costly system received a zero score and the other
    systems received a scaled score according to the following equation:

    *Score* = (100)(1-*a/b*)

    where

    *a* = cost of architecture

    *b* = cost of most expensive architecture.

    The most costly architecture is the encrypted architecture option
    (Architecture 5). This cost is \$1,782.1M. This is the value of b in
    the equation above.

[^6]: 2User cost was scaled relative to the system with the most costly
    user equipment. The system with the most costly user equipment
    received a zero score and the other systems received a scaled score
    according to the following equation:

    *Score* = (100)(1-*a/b*)

    where

    *a* = cost of user equipment

    *b* = cost of most expensive user equipment suite.

    The most costly user equipment suite is that for the encrypted
    architecture option (Architecture 5). This cost is \$157,500. This
    is the value of b in the equation above.