EVALUATION OF THE 5350-5470 MHZ AND 

5850-5925 MHZ BANDS PURSUANT TO SECTION 

6406(b) OF THE MIDDLE CLASS TAX RELIEF 

AND JOB CREATION ACT OF 2012

U.S. Department of Commerce

Rebecca Blank, Acting Secretary

Lawrence E. Strickling, Assistant Secretary

for Communications and Information

January 2013

i

EXECUTIVE SUMMARY

Through this report, the National Telecommunications and Information Administration 

(NTIA) presents the results of its initial study on the potential use of up to 195 megahertz of 

spectrum in the 5 gigahertz (GHz) band by Unlicensed-National Information Infrastructure (UNII) devices. Pursuant to Section 6406(b)(1) of the Middle Class Tax Relief and Job Creation Act of 

2012 (Tax Relief Act),1 NTIA, in consultation with the Department of Defense and other 

impacted agencies, assessed known and proposed spectrum-sharing technologies. This study 

also evaluated the risk to federal users if the Federal Communications Commission (FCC) allows

U-NII devices to operate in the 5350-5470 MHz and 5850-5925 MHz bands.2

 

Under current FCC regulations, U-NII devices are authorized to use 555 megahertz of 

spectrum in the 5150-5350 MHz and the 5470-5825 MHz bands subject to specific technical and 

operational restrictions to enable sharing with protected radar and satellite operations. U-NII 

devices provide short-range, high-speed unlicensed wireless connections in the 5 GHz band for, 

among other applications, Wi-Fi-enabled radio local area networks, cordless telephones, and 

fixed outdoor broadband transceivers used by wireless internet service providers. Unlicensed 

wireless broadband systems have become critical complements to licensed commercial mobile 

networks and to fixed wireline networks. For example, smart phones, tablets, net-books and 

laptops typically have inexpensive embedded Wi-Fi capabilities that enable high-speed 

broadband connectivity in a wide array of locations. 

International industry standards currently under development will enable the provision of 

significantly higher data throughput in the 5 GHz bands by using wider radiofrequency (RF) 

bandwidths, more data streams, and high-density signal modulation techniques. The wider RF 

bandwidth requirements may require larger blocks of contiguous frequencies and expanding the 

amount of spectrum authorized for U-NII device operation in the 5 GHz band will increase the 

contiguous spectrum that is available.

Several federal agencies currently use the two potential 5 GHz expansion bands that are 

the subject of this study. Federal systems in these bands include a variety of radar systems 

installed on airborne, ground-based, shipborne, and space-based platforms. In addition to radar 

operations, federal users operate a number of airborne RF communications systems at sites 

across the United States in these bands to conduct, for example, testing and training of unmanned 

 1

 Pub. Law No. 112-96, § 6406(b)(1), 126 Stat. 231 (Feb. 22, 2012). 

2

 Section 6406(b)(2) of Tax Relief Act requires the Assistant Secretary of Commerce for Communications and 

Information to submit to the FCC and the Committee on Energy and Commerce of the House of Representatives and 

the Committee on Commerce, Science, and Transportation of the Senate a report on the portion of the study with 

respect to the 120 megahertz in the 5350-5470 MHz band not later than eight months after the date of enactment 

(i.e., by October 22, 2012). It further requires the Assistant Secretary to submit a report on the portion of the study 

with respect to the 75 megahertz in the 5850-5925 MHz band not later than 18 months after the date of enactment 

(i.e., by August 22, 2013). NTIA, in consultation with the affected agencies, has conducted a qualitative study of 

both bands identified in the legislation and has combined the results into this single report. 
ii

aircraft systems (UAS) data and command links for intelligence, surveillance, reconnaissance 

and combat search and rescue missions. The Department of Homeland Security also operates 

UAS in the 5350-5470 MHz band for drug interdiction and border surveillance operations. In 

the 5850-5925 MHz band, additional allocated and authorized uses include non-federal fixedsatellite uplinks (Earth-to-space) and federal and non-federal mobile services. The non-federal 

mobile service allocation is limited to Dedicated Short Range Communications Service 

(DSRCS) systems operating in the Intelligent Transportation System radio service.

For this study, NTIA assumed that the federal agencies will not alter their systems or 

operations to accommodate U-NII devices on a shared basis in the potential 5 GHz expansion 

bands. NTIA also based its analysis on an assumption that the FCC’s existing requirements for 

situation-aware spectrum-sharing technologies that apply in some of the existing 5 GHz bands 

would be used to enable access to additional spectrum by new U-NII devices while preserving 

the mission capabilities of federal users. These current requirements that are implemented in 

certified and deployed equipment include transmitter power control (TPC) and dynamic 

frequency selection (DFS) approaches. However, as directed by Congress, in addition to these 

technical capabilities, NTIA also examined a range of known and proposed spectrum-sharing 

technologies and approaches, including sensing, geo-location database methods, and other 

potential co-existence measures and safeguards. 

Based on these known and proposed spectrum-sharing technologies and approaches, this 

report identifies a number of risk elements due to the likelihood of harmful interference from 

large numbers of U-NII devices to protected federal systems in the 5350-5470 MHz and 5850-

5925 MHz bands. The report discusses suggested mitigation strategies for each risk element. 

For example, the report identifies potential risks for federal airborne, ground-based, and 

shipborne radar systems related to changes in radar signal parameters or changes to U-NII device 

deployment and technical parameters, which current regulations may not be equipped to 

adequately address. Another risk element is that existing U-NII regulations were not developed 

to detect airborne signals. Suggested mitigation strategies include the development of 

representative technical parameters and sharing scenarios where the transmitters and receivers 

are not co-located to perform quantitative analysis to evaluate whether current regulations would 

protect airborne operations. The report also addresses risks and mitigation strategies to protect 

spaceborne receivers.

The report concludes that further analysis will be required to determine whether and how 

the identified risk factors can be mitigated through, for example, the promulgation of new 

safeguards in addition to the FCC’s existing requirements. Accordingly, NTIA, in collaboration 

with the federal and industry stakeholders and the FCC, will conduct quantitative analysis of 

potential mitigation requirements in connection with regulatory proceedings. In the next phase 

of its assessments, NTIA will lead detailed quantitative studies described more fully in this 

report, which will include additional analysis and measurements to evaluate the feasibility of 

existing, modified, proposed and new spectrum-sharing technologies and approaches. These 
iii

studies will be supported by and involve direct interaction between federal and non-federal

stakeholders, including representatives of the wireless industry and the intelligent transportation 

community. In addition, NTIA, the FCC, the State Department and the other affected federal 

agencies will continue to work cooperatively with industry representatives and international 

partners to fully assess various sharing scenarios in these bands and to address the international 

dimensions and ramifications of these issues.
iv
v

TABLE OF CONTENTS

EXECUTIVE SUMMARY ..........................................................................................................................................i

TABLE OF CONTENTS ........................................................................................................................................v

SECTION 1. INTRODUCTION ........................................................................................................................... 1-1

BACKGROUND...................................................................................................................................................... 1-1

OBJECTIVE............................................................................................................................................................ 1-1

APPROACH ............................................................................................................................................................ 1-2

SECTION 2. SPECTRUM-SHARING TECHNOLOGIES................................................................................ 2-1

INTRODUCTION ................................................................................................................................................... 2-1

SENSING-BASED SPECTRUM-SHARING TECHNOLOGIES....................................................................... 2-2

GEO-LOCATION-BASED SPECTRUM-SHARING TECHNOLOGIES......................................................... 2-6

BEACONING/PILOT CHANNEL SPECTRUM-SHARING APPROACHES ................................................. 2-7

U-NII DEVICE SPECTRUM-SHARING TECHNOLOGIES ............................................................................ 2-8

ADDITIONAL SAFEGUARDS TO FACILITATE SPECTRUM-SHARING ARRANGEMENTS................ 2-8

SECTION 3. U-NII DEVICE REGULATIONS AND STANDARDS ............................................................... 3-1

INTRODUCTION ................................................................................................................................................... 3-1

OVERVIEW OF FCC PART 15 REGULATIONS FOR THE 5 GHZ BAND.................................................... 3-1

INDUSTRY STANDARDS ..................................................................................................................................... 3-2

EXISTING RADAR INTERFERENCE ISSUES.................................................................................................. 3-4

SECTION 4. EVALUATION OF RISKS TO FEDERAL SYSTEMS OPERATING IN THE 5350-5470 MHZ 

BAND ........ ................................................................................................................................................... 4-1

INTRODUCTION ................................................................................................................................................... 4-1

OVERVIEW OF SYSTEMS OPERATING IN THE 5350-5470 MHZ BAND ................................................... 4-1

IDENTIFICATION OF RISKS TO SYSTEMS OPERATING IN THE 5350-5470 MHZ BAND..................... 4-3

DESCRIPTION OF RISKS TO RADAR OPERATIONS IN THE 5350-5470 MHZ BAND............................. 4-6

DESCRIPTION OF RISKS TO UAS OPERATIONS IN THE 5350-5470 MHZ BAND ................................. 4-12

DESCRIPTION OF RISKS TO SPACEBORNE SAR OPERATIONS IN THE 5350-5470 MHZ BAND ..... 4-15

ADDITIONAL SAFEGUARDS TO FACILITATE SPECTRUM-SHARING ARRANGEMENTS.............. 4-16

SECTION 5. EVALUATION OF RISKS TO FEDERAL SYSTEMS OPERATING IN THE 5850-5925 MHZ 

BAND ........ ................................................................................................................................................... 5-1

INTRODUCTION ................................................................................................................................................... 5-1

OVERVIEW OF SYSTEMS OPERATING IN THE 5850-5925 MHZ BAND ................................................... 5-1

IDENTIFICATION OF RISKS TO SYSTEMS OPERATING IN THE 5850-5925 MHZ BAND..................... 5-3

DESCRIPTION OF RISKS TO RADAR OPERATIONS IN THE 5850-5925 MHZ BAND............................. 5-6

DESCRIPTION OF RISKS TO DSRCS OPERATIONS IN THE 5850-5925 MHZ BAND ............................ 5-10

ADDITIONAL SAFEGUARDS TO FACILITATE SPECTRUM-SHARING ARRANGEMENTS.............. 5-12

SECTION 6. CONCLUSIONS .............................................................................................................................. 6-1

SCHEDULE AND MILESTONES FOR QUANTITATIVE STUDY ................................................................. 6-3

APPENDIX A: RADAR TEST WAVEFORMS................................................................................................ A-1

APPENDIX B: ASSESSMENT OF UNLICENSED-NATIONAL INFORMATION INFRASTRUCTURE 

DEVICE DEPLOYMENT AND TECHNICAL PARAMETERS .................................................................B-1

APPENDIX C: DETAILED DESCRIPTION OF DEPARTMENT OF DEFENSE 5 GHZ SYSTEMS ....... C-1

APPENDIX D: DESCRIPTION OF DEDICATED SHORT-RANGE COMMUNICATION SERVICE

SYSTEMS OPERATING IN THE 5850-5925 MHZ BAND ........................................................................... D-1

APPENDIX E: ACRONYMS AND ABBREVIATIONS ....................................................................................E-1

1-1

SECTION 1. INTRODUCTION

BACKGROUND

Section 6406(b)(1) of the Middle Class Tax Relief and Job Creation Act of 2012 (Tax 

Relief Act) requires the Assistant Secretary of Commerce for Communications and Information 

(Assistant Secretary), in consultation with the Department of Defense (DoD) and other impacted 

agencies, to conduct a study evaluating known and proposed spectrum-sharing technologies and 

the risk to federal users if the Federal Communications Commission (FCC) allowed UnlicensedNational Information Infrastructure (U-NII) devices to operate in the 5350-5470 MHz and 5850-

5925 MHz bands.

1 Under current FCC regulations, U-NII devices are authorized to use 555 

megahertz of spectrum in the 5150-5350 MHz and the 5470-5825 MHz bands subject to specific 

technical and operational restrictions to enable sharing with protected radar and satellite 

operations.2

U-NII devices provide short-range, high-speed unlicensed wireless connections in the 

5 GHz band for, among other applications, Wi-Fi-enabled radio local area networks, cordless 

telephones, and fixed outdoor broadband transceivers used by wireless internet service 

providers.3

 Unlicensed wireless broadband systems have become critical complements to 

licensed commercial mobile networks and to fixed wireline networks. For example, smart

phones, tablets, net-books and laptops typically have inexpensive Wi-Fi capabilities that enable 

high-speed broadband connectivity in a wide array of locations.

4

 

OBJECTIVE

The objective of this study was to evaluate known and proposed spectrum-sharing 

technologies and the risks to federal systems associated with allowing U-NII devices to operate 

in both the 5350-5470 MHz band and the 5850-5925 MHz band. Although the Tax Relief Act 

contemplates separate reports on both of the two potential 5 GHz expansion bands, this study 

 1

 Pub. Law No. 112-96, § 6406(b)(1), 126 Stat. 156 at 231 (Feb. 22, 2012). 

2

 See generally 47 C.F.R. Part 15, Subpart E; Revision of Parts 2 and 15 of the Commission’s Rules to permit 

Unlicensed National Information Infrastructure (U-NII) devices in the 5 GHz band, Report and Order in ET Docket 

No. 03-122, FCC 03-287 (2004), available at http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-03-287A1.pdf

(U-NII Report and Order); Memorandum and Opinion Order, ET Docket No. 03-122, FCC 06-96 (2006), available 

at http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-06-96A1.pdf (U-NII Reconsideration Order).

3

 The Wi-Fi suite of protocols includes IEEE 802.11b and 802.11g in the 2.4 GHz band, and IEEE 802.11a in the 

5.7 GHz band. See Kenneth Carter, Ahmed Lahjouji, and Neal McNeil, Unlicensed and Unshackled: A Joint OSPOET White Paper on Unlicensed Devices and Their Regulatory Issues, Office of Strategic Planning and Policy 

Analysis Working Paper Series 39 (May 2003), available at http://www.fcc.gov/working-papers/unlicensed-andunshackled-joint-osp-oet-white-paper-unlicensed-devices-and-their-regu.

4

 See FCC, Connecting America: The National Broadband Plan, Chapter 5 (Mar. 2010), available at

http://www.broadband.gov/plan/5-spectrum
combines them into a single report. Authorized incumbent systems other than those operated by 

the Federal Government are also evaluated.

5

APPROACH

NTIA, in consultation with the DoD and other impacted agencies, assessed known and 

proposed spectrum-sharing technologies and the risks to federal users associated with the 

potential introduction of U-NII devices in the 5350-5470 MHz and 5850-5925 MHz bands. The 

types of spectrum sharing technologies assessed include sensing-based approaches, geolocation/database approaches, and the use of beacons to signal the availability of frequencies to 

devices in a particular area. 

The risks identified in this report relate to the likelihood of harmful interference to 

systems operated by federal users and the study assumed that the FCC’s existing U-NII transmit 

power control (TPC) and dynamic frequency selection (DFS) regulations would be extended to 

the 5350-5470 MHz and 5850-5925 MHz bands.6 Another assumption was that the federal 

agencies will not have to alter their systems or operations to accommodate U-NII devices. The 

FCC authorizes U-NII devices under Part 15 of its rules, which provide that U-NII devices must 

operate on a non-interference basis.

7

 For each risk identified, the report discusses a suggested 

mitigation strategy and whether the strategy may adequately address the identified risk. 

NTIA developed, in collaboration with the federal agency members of the Policy and 

Plans Steering Group (PPSG), a work plan for evaluating the risks to federal systems operating 

in the 5350-5470 MHz and 5850-5925 MHz bands. The plan outlined and requested the 

technical and operational information necessary to perform the evaluation. Several federal 

agencies also conducted preliminary electromagnetic compatibility and interference analyses to 

begin to quantify risks to their systems.

 5

 Non-federal radar systems are authorized by the FCC to operate in the 5350-5470 MHz band. The military 

agencies lease capacity on commercial satellite systems authorized by the FCC operating in the 5850-5925 MHz 

band. In addition, any licensee authorized to operate DSRC roadside units may share their facilities with Federal 

Government entities and these entities may also deploy.

6

 The specific language in the Tax Relief Act referred to “risk to Federal users”. This study considered harmful 

interference to systems operated by federal users as well as systems that are used by non-federal users. “Harmful 

interference” is interference, which endangers the functioning of a radionavigation service or of other safety services 

or seriously degrades, obstructs, or repeatedly interrupts a radiocommunication service operating in accordance with 

these Regulations. “Interference” is the effect of unwanted energy due to one or a combination of emissions, 

radiations, or inductions upon reception in a radiocommunication system, manifested by any performance 

degradation, misinterpretation, or loss of information, which could be extracted in the absence of such unwanted 

energy. NTIA, Manual of Regulations and Procedures for Federal Radio Frequency Management at 6.1.1. 

7

 One of the principal operating conditions for equipment authorized under Part 15 is the operator must accept 

whatever interference is received and must correct whatever interference is caused. 47 C.F.R. Part 15, Subpart A 

(§§ 15.3(m) and 15.5); see also id. at Subpart E.
NTIA also received initial input from wireless industry stakeholders related to the projected 

technical and deployment parameters for U-NII devices,

8 and reviewed domestic and 

international technical studies used in the development of the existing U-NII regulations in 

performing this evaluation.9 NTIA is using the results of this evaluation to identify areas where 

direct interaction with wireless and transportation industry representatives is necessary and 

where more detailed quantitative analysis would be fruitful. These analyses and measurements 

could require iterative responses and constructive discussions by industry and government 

stakeholders.

 8

 See Letter from Mary L. Brown, Director, Government Affairs, Cisco Systems, Inc. to Karl Nebbia, Associate 

Administrator, Office of Spectrum Management, NTIA (Sept. 26, 2012) (Industry Input).

9

 There are several International Telecommunication Union-Radiocommunication (ITU-R) sector recommendations 

related to DFS referenced throughout this report.

2-1

SECTION 2. SPECTRUM-SHARING TECHNOLOGIES

INTRODUCTION

The Tax Relief Act requires NTIA, in consultation with DoD and other impacted 

agencies, to evaluate known and proposed spectrum-sharing technologies. This section provides 

an overview of spectrum-sharing approaches and technologies that have been recently 

authorized, identified, and addressed by the FCC as well as expert advisors to the President, 

NTIA, and the FCC. The President’s Council of Advisors on Science and Technology (PCAST) 

prepared a report that examined how advances in situation-aware spectrum-sharing technologies 

could facilitate commercial use while preserving the mission capabilities of federal users.12 The 

PCAST report notes that existing approaches to spectrum sharing can be augmented by a variety 

of means, including dynamic redirecting of devices to available frequencies and better 

prevention of harmful interference among signals in close proximity to one another. The 

Commerce Spectrum Management Advisory Committee (CSMAC) made recommendations on 

using dynamic spectrum access and geo-location/database approaches to offer new opportunities 

to increase spectrum sharing.13 Although spectrum-sharing technologies and methods have 

existed for decades, primary modern spectrum-sharing technologies use sensing-based 

approaches and geo-location/database approaches. Another new approach uses beacons or pilot 

channels to signal the availability of frequencies to devices in a particular area.

DFS, which is required by the FCC in certain bands authorized for U-NII devices, 

monitors the spectrum and selects for operation a frequency that is not already in use. For 

instance, prior to the start of any transmission, a U-NII device equipped with DFS capability 

must continually monitor the radio frequency environment for the presence of a radar signal. If a 

U-NII device determines that a radar signal is present, it must either select another channel or 

enter a “sleep mode” if no channels are available.14 

The FCC also adopted rules for Television Band Devices (TVBDs) that allow unlicensed 

devices to share unused television channels so long as the devices employ a geo-location 

database or sensing capability to determine if a channel is available.

15 The FCC initially relied

 12 President's Council of Advisors on Science and Technology (PCAST), Realizing the Full Potential of 

Government-Held Spectrum to Spur Economic Growth at 30 (July 20, 2012) (PCAST Report), available at 

http://www.whitehouse.gov/sites/default/files/microsites/ostp/pcast_spectrum_report_final_july_20_2012.pdf. 

13 NTIA, Commerce Spectrum Management Advisory Committee, Final Report of the Interference and Dynamic 

Spectrum Access Subcommittee (Nov. 8, 2010) (CSMAC Subcommittee Final Report), available at 

http://www.ntia.doc.gov/files/ntia/publications/interference-dynamic_spectrum_access_subcommittee.pdf. 

14 See U-NII Reconsideration Order at ¶ 3; U-NII Report and Order at 4.

15 See Unlicensed Operation in the TV Broadcast Bands, Second Report and Order and Memorandum Opinion and 

Order, ET Docket No. 04-186, FCC 08-260 (2008), available at

http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-08-260A1.pdf; Second Memorandum Opinion and Order, 

ET Docket No. 04-186, FCC 10-174 (2010), available at http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC10-174A1.pdf (TV White Space Second Reconsideration Order); Third Memorandum Opinion and Order, ET 
2-2

on spectrum sensing and geo-location combined with access to a database of existing spectrum 

use to determine if a channel is available. On reconsideration, the FCC eliminated the combined 

sensing/database requirement, and retained the geo-location database as the primary spectrum 

access approach, but authorized a sensing-only method based on certain criteria and conditions.16

The FCC has authorized a number of private database administrators and has begun the 

certification of TVBDs.17

The FCC’s rules governing operations in the 3650-3700 MHz band for licensed wireless 

broadband facilitate spectrum sharing through a flexible nationwide license, a database 

registration requirement for specific locations, and a requirement that operations employ 

contention-based protocols.18 The FCC relied on the wireless industry to develop standards for 

implementing this requirement, and equipment meeting this requirement is increasingly finding 

its way into the market. For example, the Institute for Electrical and Electronics Engineers

(IEEE) standard 802.11y-2008 is an amendment to the IEEE 802.11-2007 standard that enables 

high-powered Wi-Fi equipment to operate on a co-primary basis in the 3650-3700 MHz band in 

the United States.

19

SENSING-BASED SPECTRUM-SHARING TECHNOLOGIES

Sensing-based spectrum sharing approaches enable radio devices to identify unused 

spectrum by assessing and determining current use of a particular frequency through, for 

example, transmitter detection, cooperative sensing, or interference-based detection. Transmitter 

detection involves the capability of determining if a signal from another transmitter is using a 

frequency nearby by correlating a known signal with an unknown signal (matched filter 

detection), measuring signal energy (signal detection), or statistical means (cyclostationary 

feature detection or some other pattern recognition method). Cooperative sensing incorporates

information about the spectral environment from multiple sensing devices to more accurately 

 

Docket No. 04-186, FCC 12-36 (2012), available at http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-12-

36A1.pdf.

16 See TV White Space Second Reconsideration Order and 47 C.F.R. Part 15, Subpart H (§§ 15.711, 15.717).

17 See http://www.fcc.gov/encyclopedia/white-space-database-administration. 

18 See Wireless Operations in the 3650-3700 MHz Band, Report and Order, ET Docket No. 04-151, FCC 05-56 

(2005). The FCC rules define a contention-based protocol as follows: “A protocol that allows multiple users to 

share the same spectrum by defining the events that must occur when two or more transmitters attempt to 

simultaneously access the same channel and establishing rules by which a transmitter provides reasonable 

opportunities for other transmitters to operate. Such a protocol may consist of procedures for initiating new 

transmissions, procedures for determining the state of the channel (available or unavailable), and procedures for 

managing retransmissions in the event of a busy channel.” 47 C.F.R. § 90.7.

19 IEEE 802.11y-2008 - IEEE Standard for Information technology-- Local and metropolitan area networks --

Specific requirements-- Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) 

Specifications Amendment 3: 3650-3700 MHz Operation in USA, available at

http://standards.ieee.org/findstds/standard/802.11y-2008.html.
2-3

determine if spectrum is in use. Interference-based detection refers to sensing changes in the 

local noise floor to determine if additional traffic can be tolerated by primary users.20

Figure 2-1 provides an overview of sensing-based spectrum-sharing technologies.

Signal Sensing

Transmitter 

Detection

Cooperative 

Detection

Energy Detection Matched Filter 

Cyclostationary 

(Feature) Centralized Distributed

Figure 2-1. Overview of Sensing-Based Spectrum-Sharing Technologies

Energy Detection

Energy detection or threshold detection is the most common method to detect 

environmental signals because of the low computational complexity and implementation 

complexity.21 It compares energy received within a given bandwidth (BW) with a pre-defined

threshold. Observed energy less than the threshold implies that the frequency (or range of 

 20 Promoting More Efficient Use of Spectrum Through Dynamic Spectrum Use Technologies, Notice of Inquiry, ET 

Docket No. 10-237, FCC 10-198 at ¶ 20 (2010), available at 

http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-10-198A1.pdf.

21 Rawat, G. Yan and C. Bajracharya, Signal Processing Techniques for Spectrum Sensing in Cognitive Radio 

Networks, International Journal of Ultra Wideband Communications and Systems Vol. x, No, x/x (2010) 

(Techniques for Spectrum Sensing) at 4; Mansi Subhedar and Gajanan Birajdar, Spectrum Sensing Techniques in 

Cognitive Radio Networks: A Survey, International Journal of Next-Generation Networks, Vol. 3, No, 2 (June 2011) 

(Spectrum Sensing Techniques Survey) at 42; Rania Mokhtar, Rashid Saeed, and Sabira Khatun, Fifth International 

Conference: Sciences of Electronic Technologies of Information and Telecommunications, Spectrum Sensing and 

Sharing for Cognitive Radio and Advanced Spectrum Management, Tunisia (Mar 22-26, 2009) (SETIT 2009) at 6; 

Danijela Cabric, Shridhar Mubaraq Mishra, and Robert W. Brodersen, Institute for Electrical and Electronics 

Engineers, Signals, Systems and Computers 2004 Conference Record of the Thirty-Eighth Asilomar Conference, 

Implementation Issues in Spectrum Sensing for Cognitive Radios (Nov 7-10 2004) (Spectrum Sensing

Implementation Issues) at 774; Institute for Electrical and Electronics Engineers Communications Magazine, Stefan 

Geirhofer, Lang Tong, and Brian M. Sadler, Dynamic Spectrum Access in the Time Domain: Modeling and 

Exploiting White Space (DSA White Space) (May 2007) at 68.
2-4

frequencies) is not in use. This approach does not require any knowledge of the nature of the 

other transmitted signals. Under low signal-to-noise conditions, this technology may have 

difficulty differentiating environmental signals from background noise. The detection threshold 

is determined based on the operational scenario and technical parameters for the incumbent 

systems and technical and deployment characteristics of the new entrant. For example, the UNII regulations specify different detection thresholds depending on the output power of the UNII device.22

Matched Filter Detection

When the signal characteristics of other transmitted signals are known, the optimal 

detector in a stationary Gaussian noise environment is the matched filter because it maximizes 

the received signal-to-noise ratio.23 While the main advantage of the matched filter approach 

is that it requires less time to achieve high processing gain due to coherency, it requires a 

priori knowledge of the incumbent spectrum user signal such as the modulation type and 

order, the pulse shape, and the packet format. If the characteristics of the signals being 

detected are not accurately defined, matched filter detection performs poorly. Matched filters 

are often used in signal detection for radar and communication systems.24

Cyclostationary (Feature) Detection

The cyclostationary (feature) detection approach couples modulated signals with sine 

wave carriers, pulse trains, repeating spreading, hopping sequences, or cyclic prefixes, which 

result in built-in periodicity.25 These modulated signals are characterized as cyclostationary 

since their mean amplitude and autocorrelation exhibit periodicity. The mean amplitude of a 

modulated signal and the autocorrelation periodicity characteristics of a modulated signal are 

detected by analyzing a spectral correlation function. The main advantage of the spectral 

correlation function is that it differentiates the noise energy from modulated signal energy. A 

cyclostationary feature detector can perform better than an energy detector in discriminating 

 22 The existing U-NII detection thresholds were developed to protect ground-based and shipborne radar systems 

with specific operational scenarios and technical characteristics. NTIA performed a parametric analysis to 

determine the detection thresholds which considered combinations of the: number of U-NII devices, U-NII device 

antenna heights, and U-NII transmit bandwidths. Monte Carlo techniques were employed in the NTIA parametric 

analysis for the U-NII device locations, propagation losses, U-NII device antenna heights and other non-terrain 

specific losses. Changes in the operational scenarios and technical characteristics for the radar systems or the 

technical and deployment parameters for the U-NII devices would result in different detection thresholds.

23 Techniques for Spectrum Sensing at 5; Spectrum Sensing Techniques Survey at 43; SETIT 2009 at 6; Spectrum 

Sensing Implementation Issues at 774.

24 Merrill I. Skolink, Introduction to Radar Systems, Second Edition, at 369; Leon W. Couch II, Digital and Analog 

Communication Systems, Fourth Edition, at 547.

25 Institute for Electrical and Electronics Engineers Communications Society, Takeshi Ikuma and Mort NaraghiPour, A Comparison of Three Classes of Spectrum Sensing Techniques (2008) at 5; Techniques for Spectrum 

Sensing at 5; Spectrum Sensing Techniques Survey at 44; DSA White Space at 68.
2-5

against noise due to its robustness to the uncertainty in noise power. However, 

cyclostationary detection is computationally complex and can require significantly longer

observation times as compared to energy or matched filter detection approaches.

Cooperative Detection

Cooperative centralized detection collects sensing data from multiple, geographically 

dispersed devices and identifies potentially available spectrum within the area where the sensors 

were located.

26 In contrast to using a single sensor, this approach reduces the probability of 

missing information regarding local spectrum utilization; however, for a large number of devices

the sensing data collected may require larger bandwidth. Cooperative distributed detection 

devices share information with each other, but make their own estimations regarding spectrum 

use at a given location. Distributed sensing has the advantage that it does not need a backbone 

infrastructure. The network overhead information increases the requirement for more bandwidth

to share the sensing data among the cooperative nodes in the network. 

Summary of Sensing-Based Spectrum Sharing Technologies

Each approach presented has advantages and disadvantages in signal detection, which are 

summarized in Table 2-1, where the following performance parameters are compared:

- Execution Time. The ideal signal detector would work in real-time with an execution 

time is as short possible.

- Noise Rejection. The ability to be immune to Gaussian noise.

- Knowledge A-priori. How much transmitted signal information is necessary to detect 

the signal.

- Computational Complexity. Capacity calculation required to detect a signal.

- Interference Rejection. The ability to be immune to signals other than Gaussian 

noise.

Table 2-1. Summary of Sensing-Based Spectrum-Sharing Technologies

Approach Execution 

Time

Noise 

Rejection

Knowledge

A-Priori

Computational 

Complexity

Interference 

Rejection

Energy 

Detection

High Low None Low Low

Matched Filter Medium Medium High Low High

Cyclostationary Low High Medium High High

 26 Techniques for Spectrum Sensing at 6; Spectrum Sensing Techniques Survey at 45; SETIT 2009 at 7.
2-6

GEO-LOCATION-BASED SPECTRUM-SHARING TECHNOLOGIES

A database containing information about incumbent spectrum users, when combined 

with a geo-location system such as the Global Positioning System and an interference-free 

location-data communications link, provides a mechanism to facilitate spectrum sharing with 

incumbents operating at fixed or known locations with known technical parameters.

27 This 

approach requires the development of a database infrastructure, use of a management control 

system (e.g., with the ability to send timely and accurate information to remote devices), sharing 

of technical and deployment parameters for specific systems operating in the frequency bands, 

and an over-the-air system identification. Geo-location spectrum-sharing technologies can be 

used in conjunction with a well maintained, current database to define geographic areas where 

device operation will and will not be permitted, or where limitations should be placed on the 

operating parameters to enable spectrum sharing (e.g., reduction of power). 

The information needed for the database (specific technical parameters, usage contours, 

protection contours) would have to be pre-determined. A determination is needed as to whether 

the database can provide accurate information regarding spectrum use on a real-time basis or at 

specified time intervals. Questions related to building and administering the database and 

handling sensitive or classified system parameters would have to be addressed. Procedures for 

ensuring devices have appropriate authorization to access the database would also have to be 

developed. To date, geo-location based spectrum-sharing technology has primarily been used to 

facilitate sharing with fixed systems. This technology has not been deployed with mobile 

systems, such as the transportable ground-based, shipborne, and airborne radar systems that 

operate in the 5350-5470 MHz and 5850-5925 MHz bands. 

In examining new approaches to spectrum allocation, the PCAST recommended 

implementing a real-time or near real-time dynamic database, Spectrum Access System (SAS) to 

govern shared access to federal frequency bands.28 The PCAST believes that shared use can be 

coordinated primarily by registering and communicating with a management database, similar to 

the White Space Databases certified by the FCC. The SAS would serve as an information and 

control clearinghouse for band-by-band registrations and conditions of use that would apply to 

all users. The database would enable a number of distinct operational functions.

29 For example, 

devices would be certified for secondary and opportunistic access only if they could connect to 

the database and periodically seek renewed transmit permission and/or terms of use updates 

required for each band authorized. The SAS would require automatic connection to a database to

ensure that no devices are operating under out-of-date terms of use or without the capacity to be 

denied access to a particular band when necessary. The system of certification, registration, and 

 27 CSMAC Subcommittee Final Report at Section 3.3.

28 PCAST Report at 24.

29 Id. at 101.
2-7

authentication through a geo-location database would also facilitate enforcement, since the 

identity, manufacturer, and recent location(s) of errant devices could be readily determined from 

transactional data collected by the database.

BEACONING/PILOT CHANNEL SPECTRUM-SHARING APPROACHES

In a beacon spectrum-sharing approach, a new entrant’s transceiver must have the ability 

to receive a control signal sent continuously by the incumbent systems at times when 

transmissions by the new entrant are permitted. The new entrant may not commence 

transmissions if beacon signals are not received, and if any beacon signal is present but then 

stops while the new entrant is transmitting, transmissions must cease within a specified time 

interval. The beacons could be a radio frequency signal sent by incumbents on designated 

control frequencies, or they may be signals received over a physical connection such as fiber, 

copper, or coaxial cable. Transmission by the new entrant would cease if any beacon signal 

suffers from unfavorable propagation conditions or the physical connection is lost such that the 

beacon signals are not properly received by the new entrant. In other words, the incumbent has 

“fail-safe” protection against harmful interference, because if the new entrant cannot hear the 

beacon signal, it must cease transmission.

The Institute of Electrical and Electronics Engineers developed a standard that defines the 

air interface (protocol and data formats) for communication devices that form a beaconing 

network that offers an enhanced protection method to help prevent harmful interference with 

low-power, licensed devices operating in television broadcast bands.30 The beacons transmit 

identifiable synchronization bursts as well as, optionally, information about locations and 

operational parameters of the protected systems.

Several of the systems operating in the 5350-5470 MHz and 5850-5925 MHz bands 

operate in sensitive or classified locations, resulting in an operational security risk if this 

spectrum-sharing technology is employed. Additionally, the implementation of this sharing 

technique would require the modification of all incumbent systems to include the beacon 

transmitter. 

 30 IEEE Std 802.22.1-2010, IEEE Standard for Information Technology – Telecommunications and information 

exchange between systems Local and metropolitan area networks – Specific requirements Part 22.1: Standard to 

Enhance Harmful Interference Protection for Low-Power Licensed Devices Operating in the TV Broadcast Bands

(Nov. 1, 2010).
2-8

U-NII DEVICE SPECTRUM-SHARING TECHNOLOGIES

The U-NII devices currently authorized to operate in the 5250-5350 MHz and 5470-

5725 MHz bands employ TPC and DFS capabilities, which are discussed in the next section.

DFS is a form of sensing-based sharing technology that requires signal detection where 

knowledge of certain parameters of the radar signal such as pulsewidth, pulse repetition 

interval, and the number of pulses per burst are used to improve signal detection.31 This study 

considered both signal sensing and geo-location spectrum-sharing technologies in connection 

with the potential introduction of U-NII devices in the 5350-5470 MHz and 5850-5925 MHz 

bands. These spectrum-sharing technologies are already in use by unlicensed devices. On the 

other hand, even though cooperative sensing between U-NII access points and client devices is 

feasible, sharing sensing data among different unlicensed devices has not been addressed in the 

industry standards bodies for unlicensed devices. Beaconing and pilot channel approaches, while 

the subject of industry standards in connection with other frequency bands and applications, do 

not appear to be employed at this time. Accordingly, NTIA considered the spectrum-sharing

technologies shown in Table 2-2 in its qualitative evaluation.

Table 2-2. U-NII Device Spectrum-Sharing Technologies 

Spectrum-Sharing 

Technology Description

Energy Detection

A spectrum-sharing technology where the detection level is defined by detecting a 

received signal strength in a reference bandwidth that is greater than a specified 

threshold

Signal Detection A spectrum-sharing technology that employs a combination of threshold detection 

and signal parameter pattern recognition

Energy Detection 

and Geo-Location

A spectrum-sharing technology that employs a combination of threshold detection 

and geo-location/database capability

Signal Detection and 

Geo-Location

A spectrum-sharing technology that employs a combination of signal detection 

and geo-location/database capability

ADDITIONAL SAFEGUARDS TO FACILITATE SPECTRUM-SHARING 

ARRANGEMENTS

Where the spectrum-sharing technologies in Table 2-2 may not adequately address the 

identified risk to incumbent systems, NTIA, as part of its upcoming quantitative study, will 

identify additional regulatory or technical approaches that could facilitate sharing arrangements. 

These include assumptions or restrictions such as power limits, indoor/outdoor deployment, TPC 

requirements, and policy-based device management. 

 31 The IEEE Standard Dictionary of Electrical and Electronics Terms (ANSI/IEEE Std 100-1988) defines 

pulsewidth as the time interval between half-power points on the trailing and leading edges of the pulse and the 

pulse repetition interval as the time duration between successive pulses.
3-1

SECTION 3. U-NII DEVICE REGULATIONS AND STANDARDS

INTRODUCTION

This section provides an overview of FCC regulations and industry standards related to 

U-NII devices. The existing FCC regulations for U-NII DFS-enabled devices were developed 

jointly between NTIA, the FCC, the federal agencies, and industry representatives over an 

approximate five-year time period. During that time, the agencies and industry worked together 

on analysis and measurements (laboratory and field) in support of the final rules and the 

certification measurement procedures that the FCC adopted.

32

OVERVIEW OF FCC PART 15 REGULATIONS FOR THE 5 GHZ BAND

Under its Part 15 Rules, the FCC authorizes U-NII devices to operate in the 5150-

5350 MHz and 5470-5825 MHz bands.33 Table 3-1 summarizes the maximum allowable 

equivalent isotropically radiated power (EIRP), DFS requirements, and limitations on operational 

deployment for each frequency band authorized for U-NII device operation.

Table 3-1. Summary of U-NII DFS Technical and Operational Parameters

Frequency Band

(MHz)

U-NII Band 

Identifier

Maximum 

Allowable EIRP

(dBm)

DFS Required Operational 

Deployment

5150-5250 UNII-1 23 No Indoor Only

5250-5350 and

5470-572534 UNII-2 30 Yes Indoor and Outdoor

5725-582535 UNII-3 53 No Indoor and Outdoor

The Part 15 U-NII rules specify DFS detection thresholds based on the EIRP of the 

device: -64 dBm for devices with a maximum EIRP of greater than 23 dBm and -62 dBm for 

devices with a maximum EIRP of less than 23 dBm.36 These detection thresholds are applicable 

to the DFS channel availability check and in-service monitoring functions described below:

Channel Availability Check - a check where the U-NII device listens on a particular 

channel to identify whether there is a radar operating on that radio channel.

 32 The FCC U-NII regulations were developed over a five year timeframe which began in March 2002 and ended 

with the FCC issuing compliance measurement procedure in April 2007. See Office of Engineering and Technology 

Laboratory Division Knowledge Database, Publication Number: 905462 (Apr. 17, 2007), available at

https://apps.fcc.gov/kdb/GetAttachment.html?id=PIDuzGyOggplxY%2F09X8mgA%3D%3D.

33 See 47 C.F.R. Part 15, Subpart E.

34 U-NII devices operating in these bands at peak power are required to reduce by the amount in dB that the 

directional gain exceeds 6 dBi. See 47 C.F.R § 15.407(a)(1). 

35 U-NII devices operating in this band can employ a directional antenna with a maximum gain of 23 dBi without 

any reduction in the peak transmitter output power. See 47 C.F.R § 15.407(a)(3). 

36 See 47 C.F.R. § 15.407(h)(2).
3-2

In-Service Monitoring - a mechanism to check a channel in use by the U-NII device for 

the presence of a radar. 

The rules establish a 60-second time period for the channel availability check time. The 

radio frequency (RF) channel move time is defined as a period of 10 seconds during which all 

transmissions on a RF channel must cease. Transmissions during this period consist of normal 

traffic for typically less than 100 milliseconds and a maximum of 200 milliseconds after 

detection of a radar signal. Intermittent management and control signals can be sent during the 

remaining time to facilitate vacating the operating RF channel. The aggregate time of the 

intermittent management and control signals is typically less than 20 milliseconds. A RF 

channel on which a radar was detected either during the channel availability check or in-service 

monitoring is subject to a 30 minute non-occupancy period.37

The current regulations define two types of U-NII devices: access point devices and 

client devices. Access point devices can initiate a network and client devices cannot transmit 

until an enabling signal is received from an access point. In the current implementation, DFS 

functionality is delegated to access point devices. 

U-NII devices operating in the 5250-5350 MHz and 5470-5725 MHz bands with an EIRP 

of greater than 27 dBm must employ a TPC mechanism. The FCC also has certification 

measurement procedures for U-NII devices operating in the 5250-5350 MHz and 5470-5725 MHz 

bands, including test waveforms based on the characteristics of representative radar systems.38 

Appendix A provides an overview of the radar signal parameters used in FCC certification of UNII devices.

INDUSTRY STANDARDS

The IEEE 802.11h39 and 802.11n40 standards govern wireless networking transmission 

methods for unlicensed devices in the 5 GHz bands. IEEE 802.11ac is a standard under 

development, which will provide higher throughput in the 5 GHz bands. It will enable multistation throughput of at least 1 gigabit per second and a maximum single link throughput of at 

least 500 megabits per second, by using wider RF bandwidths (80 MHz or 160 MHz), more data 

streams (up to eight), and high-density modulation (up to 256 Quadrature Amplitude 

 37 Id.

38 See U-NII Reconsideration Order.

39 IEEE 802.11h, IEEE Standard for Information technology – Telecommunications and information exchange 

between systems – Local and metropolitan area networks – Specific requirements Part 11: Wireless LAN Medium 

Access Control (MAC) and Physical Layer (PHY) specifications Amendment 5: Spectrum and Transmit Power 

Management Extensions in the 5 GHz band in Europe (2003).

40 IEEE 802.11n, IEEE Standard for Information technology – Telecommunications and information exchange 

between systems – Local and metropolitan area networks – Specific requirements Part 11: Wireless LAN Medium 

Access Control (MAC) and Physical Layer (PHY) specifications Amendment 5: Enhancements for Higher 

Throughput (2009).
3-3

Modulation). U-NII devices developed on the 802.11h and 802.11n standards have RF 

bandwidths of 20 MHz and 40 MHz, respectively.

As shown in Figure 3-1 below, the wider RF bandwidths supported by the IEEE 802.11ac 

standard require large blocks of contiguous spectrum.41

UNII-1: 5150-5250 MHz band

UNII-2: 5250-5350 MHz and 5470-5725 MHz band

UNII-3: 5725-5825 MHz band

Figure 3-1. Currently Available and New 5 GHz Channels 

While the currently available channels support a number of combinations of these wider RF 

bandwidth channels, expanding the amount of spectrum authorized for U-NII device operation in 

the 5 GHz frequency range will increase the contiguous spectrum available to accommodate 

broadband applications. As shown in Figure 3-1, additional unlicensed use of 5.35-5.47 GHz 

and 5.85-5.925 GHz would allow nine 80 MHz channels and four 160 MHz channels (shown in 

red).

The FCC has provided guidance for testing of IEEE 802.11ac and pre-ac devices for 

compliance with Section 15.247 and 15 subpart E (Section 15.401 through Section 15.407) of 

their rules.42 All transmissions above 5.725 GHz must be under Section 15.407 whenever 

operating on a channel where the emission bandwidth crosses 5.725 GHz. The part of the 

transmission that is below 5.725 GHz is in a band that is permitted only under the Section 15.407 

rules. The part of the transmission that is above 5.725 GHz is in a band that could normally be 

permitted under either Section 15.247 or Section 15.407, but because part of the signal is covered 

only by Section 15.407, the entire signal must comply with Section 15.407.

 41 This figure was presented in https://mentor.ieee.org/802.11/dcn/12/11-12-1159-03-00ai-masers-slaves-andclients.pptx.

42 See Office of Engineering and Technology Laboratory Division Knowledge Database, Publication Number: 

644545 (June 7, 2012).
3-4

EXISTING RADAR INTERFERENCE ISSUES

In 2009, the Federal Aviation Administration (FAA) became aware of interference to its

Terminal Doppler Weather Radar (TDWR) systems that operate in the 5600-5650 MHz band. 

These radars provide quantitative measurements of gust fronts, wind shear, microbursts, and 

other weather hazards for improving the safety of operations in and around 45 major airports.

At the request of the FAA, NTIA and the FCC conducted an interference investigation

that concluded interference was being caused by U-NII devices and unlicensed devices operating 

in the 5725-5850 MHz band pursuant to Section 15.247 of the FCC’s rules with buildingmounted, high-gain antennas (unobstructed view to TDWR) for outdoor point-to-point 

communications links.43 There have not been any cases of TDWR interference identified for 

other unlicensed device applications. The investigation identified the following causes of 

interference:

- unlicensed device did not employ DFS and was modified to operate in the 5470-5725 

MHz band;

- U-NII device DFS functionality was available but was disabled by the operator;

- U-NII device DFS functionality performed properly, causing the device to move to an 

adjacent channel, but still caused interference; 

- unlicensed device was not certified by the FCC;

- unlicensed device was not certified by the FCC to operate in the bands authorized for 

U-NII devices (e.g., Section 15.247);

- unlicensed device and antenna combinations were not certified by the FCC;

- U-NII device complied with FCC DFS certification requirements but failed to detect 

TDWR; and 

- U-NII DFS compliance test waveforms did not accurately represent all of the TDWR 

modes of operation.

Results of this investigation led to the FCC to temporarily suspend granting new 

equipment authorizations for access point devices in mid-2009 while it worked on ways to 

mitigate these problems. On October 8, 2009, the FCC introduced interim measures that 

 43 NTIA Technical Report TR-11-473, Case Study: Investigation of Interference into 5 GHz Weather Radars from 

Unlicensed National Information Infrastructure Devices, Part I (Nov. 2010), available at

http://www.its.bldrdoc.gov/publications/2548.aspx (NTIA Case Study Part I); NTIA Technical Report TR-11-479, 

Case Study: Investigation of Interference into 5 GHz Weather Radars from Unlicensed National Information 

Infrastructure Devices, Part II (July 2011), available at http://www.its.bldrdoc.gov/publications/2554.aspx (NTIA

Case Study Part II); and NTIA Technical Report TR-12-486, Case Study: Investigation of Interference into 5 GHz 

Weather Radars from Unlicensed National Information Infrastructure Devices, Part III (June 2012) , available at

http://www.its.bldrdoc.gov/publications/2677.aspx (NTIA Case Study Part III).
3-5

restricted the approval of access points in the 5470-5725 MHz band to devices operating indoors

and placed restrictions on the approval of certain U-NII access point devices.

44

Subsequently, the FCC has allowed outside operation with the following restrictions: UNII devices must be professionally installed; operations are not allowed in the 5600–5650 MHz 

band (TDWR frequencies); and U-NII devices within 35 kilometers of a TDWR location shall be 

separated by at least 30 MHz (center frequency-to-center frequency) from the TDWR operating 

frequency.45 The Wireless Internet Service Provider Association created the U-NII Device

Interference Advisor (UDIA), an online database and registry containing detailed information 

about TDWR systems and registered U-NII devices.46 This tool allows a network operator or 

installer to search and confirm if their device is operating within 35 km proximity of TDWR 

site(s) and voluntarily register certain technical information into the online database.47 Federal 

government personnel can search this single resource to quickly identify registered network 

operators and determine which operators may be interfering with TDWR devices. Access to 

registration data is restricted to the FCC, the FAA, and to individual network operators.

The FCC has continued to work with industry, the FAA, and NTIA to address 

interference to TDWR systems. However, instances of interference to TDWRs continue. A 

majority of the fully documented interference cases have involved the operation of high-power 

systems deployed with high-gain antenna. A vast majority are due to unauthorized operation of 

devices rather than failure of a properly operating U-NII device. NTIA is not aware of any

documented cases of harmful interference from U-NII devices used for low power applications 

such as laptop computers, tablets, or smart phones. 

The interference to TDWR demonstrates the importance of the FCC certification and 

enforcement processes that must be taken into consideration to effectively preclude harmful 

interference if U-NII device operations are authorized in the 5350-5470 MHz and 5850-5925 MHz 

bands. NTIA anticipates that a forthcoming FCC proceeding will address certification and 

enforcement issues for U-NII devices that were identified as part of the TDWR interference 

investigation.

 44 As a result of the TDWR interference investigation the FCC has taken a number of enforcement actions where 

the operators had caused interference or used unauthorized equipment. A list of the FCC enforcement activities is 

publicly available at http://www.fcc.gov/encyclopedia/weather-radar-interference-enforcement.

45 FCC Office of Engineering and Technology, Approval of DFS U-NII Devices v01, KDB 443999 D01 (Oct. 14, 

2010), available at http://apps.fcc.gov/oetcf/kdb/forms/FTSSearchResultPage.cfm?switch=P&id=41732. 

46 The Wireless Internet Service Providers Association and Spectrum Bridge Inc. Press Release, Spectrum Database 

Solution Enables Access to 5GHz Spectrum Previously Unavailable Due to Interference Issues (July 27, 2010), 

available at

http://www.spectrumbridge.com/Libraries/Press_Releases/Spectrum_Database_Solution_Enables_Access_to_5GHz

_Spectrum_Previously_Unavailable_Due_to_Interference_Issues_July_27_2010.sflb.ashx. 

47 The UDIA database is available at http://www.spectrumbridge.com/udia/search.aspx.
3-6

In an earlier effort culminating with the publication of a Technical Report in 2006, NTIA 

examined critical questions regarding the robustness of radar receiver performance in the presence 

of RF interference, especially at low levels.

48 The report concluded that, based on wide-ranging 

interference measurements performed on many representative radar receivers, the loss of targets at 

low interference levels was “insidious” as there was no overt indication to the radar operators or 

even to sophisticated radar software that losses were occurring. According to this report, it was 

unlikely that such interference would be reported to spectrum management authorities, even when 

radars experienced serious performance degradation due to low-level interference, because the 

operators “would probably not be aware that targets that should otherwise have been detected were 

missing, nor that any interference was occurring.” The loss of targets due to interference was not 

directly related to the distance of the targets from the radar.

 48 NTIA Technical Report TR-06-444, Effects of RF Interference on Radar Receivers at 137 (Sept. 2006), available 

at http://www.its.bldrdoc.gov/publications/2481.aspx (Technical Report TR-06-444). 
4-1

SECTION 4. EVALUATION OF RISKS TO FEDERAL SYSTEMS 

OPERATING IN THE 5350-5470 MHZ BAND

INTRODUCTION

This section describes the risks to federal systems and possible mitigation strategies 

associated with allowing U-NII devices to operate in the 5350-5470 MHz band.

OVERVIEW OF SYSTEMS OPERATING IN THE 5350-5470 MHZ BAND

The 5350-5470 MHz band is allocated for both federal and non-federal use on a primary 

basis. The federal allocations on a primary basis are to the Earth exploration-satellite, space 

research, and radiolocation services. Additionally, federal and non-federal primary allocations 

include aeronautical radionavigation in the 5350-5460 MHz band and radionavigation in the 

5460-5470 MHz band. An overview of the federal systems operating in the 5350-5470 MHz 

band is provided below. Appendix C provides a more detailed description of DoD systems 

operating in the band.

Radar Systems

The DoD uses the 5350-5470 MHz band for a wide variety of applications. Range and 

tracking radar systems are the prime tracking system for range safety that is essential for 

protection of life and property when testing non-cooperative targets, which include many 

weapon systems tested or used in training on DoD test and training ranges. Tactical anti-air 

warfare radar systems are part of an advanced ground-based air defense missile system. Other 

tactical radars operating in this band include shipborne radars for surface search, navigation, and 

weapons fire control. Airborne weather navigation radars for storm avoidance also operate in 

this band. These military radars have the operational capability to tune across the entire 5250-

5725 MHz frequency range and can either operate on a fixed frequency or employ frequency 

hopping techniques. In the past, these radars have operated on or near military installations. 

However, situations may arise where these radars have to be used more widely in support of 

homeland security. One of the areas of concern in assessing interference to military radars stems 

from future radar deployments and the expanding role of military radars in support of homeland 

defense. This expanded role could result in a requirement to deploy military radars in cities and 

metropolitan areas where unlicensed devices will have their highest usage.

The Coast Guard also operates shipborne radars, which are used by National Security 

Cutters while performing the following missions: defense readiness; drug interdiction; other law 

enforcement actions such as patrolling fisheries, ports, waterways, and coastal areas; search and 

rescue; and marine environmental protection. Radar systems operating in this band provide ships 

with surface search and navigation capabilities and tracking services, particularly during 

inclement weather. These radars are vital sensors for safe navigation of waterways.

The Federal Aviation Administration mandates that aircraft operating under 14 Code of 

Federal Regulations (14 C.F.R.) Part 121 and certain aircraft operating under 14 C.F.R. Parts 91 
4-2

and 135 carry weather radars to provide the pilots with weather information for safe aeronautical

navigation. Some of the early radar equipment installed on these aircraft still use the 5350-5470 

MHz frequency band. Theses radars can be used at various altitudes for weather as well as 

microburst detection. 

In addition to the radar systems used by the DoD, several other agencies operate radar 

systems in the band. The National Aeronautics and Space Administration (NASA) uses this 

band for test and launch range instrumentation radars to track rockets, missiles, satellites, 

launched vehicles, and other targets. These radars are usually the prime coverage system for 

range safety. Range instrumentation radar transponders also operate in the band to enhance radar 

tracking of low cross-section aircraft and missiles and systems under test. The National Oceanic 

and Atmospheric Administration operates radar systems in the band on “Hurricane Hunter” 

aircraft. The Department of Energy operates radar systems and associated transponders in the 

band at two specified test ranges in the United States. 

Airborne Systems

The DoD operates several airborne systems in this band. Aeronautical telemetering 

mobile stations in this band for transmit data directly related to the airborne testing of vehicles or 

major components such as rockets, missiles, and vehicles.

49 This band also supports the testing 

of unmanned aircraft system (UAS) datalinks from aircraft-to-ground and from ground-toaircraft. The UAS datalink provides command and control information from the ground control 

station (GCS) to the UAS using the command link. Payload data and UAS status information are 

transmitted from the UAS to the GCS using a return link. The command link, a ground data 

terminal transmitter, operates at 5625-5850 MHz and the return link (UAS transmitter) transmits 

at 5250-5475 MHz. The Army, Navy, and Air Force operate UAS in the 5 GHz frequency range 

for intelligence, surveillance, and reconnaissance; combat search and rescue; convoy and raid 

over-watch; and real-time full-motion video for target development. These agencies conduct test 

and training in support of these missions at sites in the United States. In addition, sense-andavoid radar systems are being developed to permit autonomous operation of unmanned aircraft,

and diagnostic radars are being developed to test low-observable materials. The Department of 

Homeland Security (DHS) also operates UAS in this band for drug interdiction and border 

surveillance operations. The NASA also operates a limited number of systems in the 5350-

5470 MHz band that are used for downlink transmissions of data to ground control receivers.

Spaceborne Synthetic Aperture Radar Systems

NASA, in a joint venture with the French agency, Centre National d'Etudes Spatiales, 

operates a space-based altimeter system in the 5140-5460 MHz band that is used to obtain 

measurements of the Earth’s ocean surface height. 

 49 There is no frequency allocation for UAS operations in the 5350-5470 MHz band; however, NTIA has authorized 

federal agencies to operate UAS systems throughout the United States.
4-3

Synthetic aperture radar (SAR) systems in the 5350-5470 MHz band perform spacebased observations and measurements of surface topography, soil moisture, and sea surface 

height. Active sensing is the measurement on board a spacecraft of signals transmitted by a 

sensor and then reflected, refracted, or scattered by the Earth’s surface or its atmosphere. The 

higher quality data collected using wideband SARs allow scientists to gain new insight into the 

prediction of climatic changes. These wideband SARs also provide the higher resolution 

necessary for commercial applications, such as high-resolution surface mapping.50

Canada operates an Earth exploration-satellite, known as RADARSAT, in the 5350-

5470 MHz band to provide mission critical data in support of national security, public safety, law 

enforcement, and civilian applications in Canada and the United States.51 These applications 

include disaster management; response and recovery for safety of life; ice monitoring;

surveillance including maritime domain awareness; oil spill response; hydrology; mapping; 

geology; safety of navigation; agriculture; and forestry. Federal agencies use the data collected 

by spaceborne synthetic aperture radar systems. For example, the United States Coast Guard 

International Ice Patrol uses RADARSAT data operationally to detect and track icebergs. In 

assessing the feasibility of allowing U-NII device operation in the 5350-5470 MHz band, NTIA 

will examine the potential impact to the RADARSAT and other spaceborne synthetic aperture 

radar systems as part of this qualitative study.

IDENTIFICATION OF RISKS TO SYSTEMS OPERATING IN THE 5350-5470 MHZ

BAND

This report identifies risks based on the potential for interference to federal systems if UNII devices are allowed to operate in the 5350-5470 MHz band. The technical and operational 

characteristics of federal systems and/or the technical and deployment parameters of the U-NII 

devices affect the risk. These risks also arise from the premise that the FCC may authorize UNII DFS devices using its current regulations. Where feasible, the federal agencies conducted 

preliminary analyses using the existing U-NII regulations and estimated deployment parameters 

to quantify the interference risks. Table 4-1 provides an overview of the risk elements and 

suggested mitigation strategies for each category of system associated with allowing U-NII 

device operation in the 5350-5470 MHz band.

 50 For example, wide bandwidth SARs can precisely map the boundary of oil spills to a resolution of 1 meter.

51 See letter from Helen McDonald, Senior Assistant Deputy Minister, Spectrum, Information Technologies and 

Telecommunication, Industry Canada to Karl Nebbia, Associate Administrator, Office of Spectrum Management, 

NTIA (July 6, 2012). A copy of this letter is available upon request.
4-4

Table 4-1. Overview of Risk Elements and Suggested Mitigation Strategies Associated with the 5350-5470 MHz Band

System

Category Description of Risk Element Suggested Mitigation Strategy

Radar Risk Element 1 - Changes in radar signal 

parameters may impact U-NII device 

detection of radar systems.

- Review radar signal parameters used in the development of existing regulations and 

assess whether existing U-NII device spectrum sharing technologies can be used to 

protect current and future radar systems.

Risk Element 2 - Changes in U-NII device 

deployment and technical parameters may 

result in harmful interference.

- Update U-NII device deployment and technical parameters used in quantitative 

analysis.

Risk Element 3 - Existing U-NII regulations 

may not adequately protect current and future 

radar systems from serious degradation.

- Identify new sharing scenarios for current and future radar systems.

- Perform quantitative analysis to evaluate current DFS regulations. 

Risk Element 4 - Changes to existing U-NII 

DFS detection parameters may not protect 

current and future radar systems from serious 

degradation.

- Develop representative test signals for laboratory measurements to verify DFS 

detection capabilities.

- Perform laboratory measurements using prototype devices and simulated radar 

signals.

- Perform field measurements using actual radar signals to verify laboratory 

measurements.

- Modify existing DFS regulations based on the results of quantitative analysis and 

measurements.

Risk Element 5 – Existing U-NII regulations 

may introduce “hidden node” interference that 

seriously degrades performance.

- Examine the conditions under which “hidden node” interference exists.

- Modify existing U-NII device regulations as needed to resolve “hidden node” 

interference. 

Risk Element 6 – U-NII devices operating on 

an adjacent channel may cause harmful 

interference to radar systems.

- Perform quantitative analysis to assess the impacts of adjacent channel interference.

- Perform measurements to evaluate different options for addressing adjacent channel 

interference.

- Modify existing U-NII device regulations based on the results of quantitative

analysis and measurements.

Risk Element 7 – Radar receiver interference 

protection criteria used to develop existing 

U-NII DFS regulations may not address lowlevel interference effects.

- Evaluate the interference protection criteria used in the development of the current

DFS regulations to determine if they adequately protect radar systems from lowlevel interference effects.

- If necessary revise the interference protection criteria to address low-level 

interference effects.

Risk Element 8 – Channel response time 

requirements in the current DFS regulations 

may not be adequate to protect all radar 

system operational scenarios. 

- Perform analysis to determine if it is necessary to add a channel response time to the 

DFS regulations to protect radar systems operating in different scenarios.

- Modify the existing U-NII DFS device certification test procedures based on the 

results of the analysis.
4-5

Table 4-1. Overview of Risk Elements and Suggested Mitigation Strategies Associated with the 5350-5470 MHz Band (Continued)

System

Category Description of Risk Element Suggested Mitigation Strategy

Airborne 

Systems Risk Element 1 - Existing U-NII regulations 

were not developed to detect airborne signals.

- Develop representative technical parameters and sharing scenarios to examine 

impact to ground-based and airborne operations.

- Perform quantitative analysis to evaluate whether current DFS regulations 

protect airborne operations.

Risk Element 2 - U-NII signal detection 

technologies may not be capable of detecting 

airborne signals resulting in serious 

performance degradation.

- Determine if current signal detection techniques for sharing among U-NII 

devices can be used or adapted to detect ground-based and airborne signals.

Risk Element 3 - Current U-NII regulations 

were not developed to protect systems where 

the transmitter and receiver are not co-located.

- Examine the conditions under which a “hidden node” problem exists.

- Identify any possible sharing approaches for more detailed quantitative analysis.

Risk Element 4 - Changes to U-NII DFS 

detection parameters may not protect airborne

operations from performance degradation.

- Develop representative test signals for laboratory measurements to verify DFS 

detection capabilities.

- Perform laboratory measurements using prototype devices and simulated 

airborne signals. 

- Perform field measurements using actual airborne signals to verify laboratory 

measurements.

- Modify existing DFS regulations based on the results of the analysis and 

measurements.

SAR Risk Element 1- Existing U-NII regulations 

were not developed to protect spaceborne 

receivers.

- Perform quantitative analysis to assess the potential interference impact to SAR 

receivers.

- Determine if limitations on U-NII device deployment and technical parameters 

will mitigate interference to SAR receivers.
4-6

DESCRIPTION OF RISKS TO RADAR OPERATIONS IN THE 5350-5470 MHZ BAND

Risk Element 1 - Changes in Radar Signal Parameters May Impact U-NII Device Detection of 

Radar Systems 

The following paragraphs evaluate the impact on different spectrum-sharing technologies 

related to the risk associated with new signal parameters of federal radar systems.

Energy Detection. This spectrum-sharing technology performs signal sensing during the channel 

availability check and in-service monitoring functions using a dedicated listen time (e.g., no data 

transmissions). A dedicated listen time eliminates reliance on using the specific parameters of the 

radar signal (e.g., pulse width, pulse repetition interval) to detect the presence of a radar system. 

Since this spectrum-sharing technology does not require knowledge of radar signal characteristics, it 

will minimize the risk associated with changes in the signal parameters that can impact the detection 

of ground-based, airborne, and shipborne radar systems operating in the 5350-5470 MHz band. 

However, recently fielded and in-development radar systems that include low-power modes or are 

designed to avoid detection to meet their mission requirements may present challenges for this 

spectrum-sharing technology. If set too low, the U-NII devices may be unable to determine the 

difference between a radar and another U-NII device.

Matched Filter Detection. Matched filter detection technology requires prior knowledge of the 

characteristics of radar signals to be effective. Defining the specific characteristics for federal 

radar signals is not possible because this would limit future radar system design. To allow 

greater flexibility for future radar designs, signals must be defined in terms of ranges of 

parameters as in the existing U-NII regulations described in Appendix A. Matched filter 

detection may not be effective for sharing between U-NII devices and federal radar systems in 

the 5350-5470 MHz band given that the exact characteristics of the radar signals cannot be 

rigidly specified and are subject to change.52 This spectrum-sharing technology will not address 

the risk associated with changes in the radar signal parameters that can impact detection of radar 

systems.

Signal Detection. Signal detection employs a combination of threshold detection and signal 

parameter pattern recognition. This spectrum-sharing technology is currently employed by U-NII 

DFS devices operating in the 5250-5350 MHz and 5470-5725 MHz bands where radar signal 

parameters such as pulse width, pulse repetition interval, and the number of pulses per burst are 

known and can be used to improve signal detection. Using this technology, devices perform 

signal sensing in the quiet periods between data transmissions as described in Annex 4 of 

Recommendation ITU-R M.1652.53 It is highly dependent on the transmission characteristics of the 

 52 Changes in mission requirements and the targets to be detected can result in the development of new radar signals. A 

spectrum sharing technology must be adaptable to these signals changes and cannot constrain the development of future 

radar systems.

53 Recommendation ITU-R M.1652, Dynamic Frequency Selection (DFS) in Wireless Access Systems Including Radio 

Local Area Networks for the Purpose of Protecting the Radiodetermination Service in the 5 GHz Band (2003).
4-7

U-NII devices and the parameters defining the radar signals. Any changes to the radar signal 

parameters described in Appendix A and/or U-NII device transmission characteristics could impact 

the detection capabilities of the U-NII devices and increase the potential for interference to federal 

radar systems. The transmission characteristics of the higher data rate signals envisioned under the 

IEEE 802.11ac standard will tend to reduce the time during which a U-NII device is sensing. This 

reduced sensing time, in conjunction with radar systems that employ pulsed signals with narrower 

pulsewidths and/or lower pulse repetition rates, will impact U-NII device detection capabilities and 

needs to be analyzed in more detail to determine if this spectrum-sharing technology addresses the 

identified risk.54 In addition, recently fielded and in-development radar systems that include lowpower modes or are designed to avoid detection to meet their mission requirements, may present 

challenges for this spectrum sharing technology.

Geo-Location. FCC regulations do not require U-NII DFS devices to implement geo-location 

technology for sharing with federal radar systems operating in the 5250-5350 MHz and 5470-

5725 MHz bands.55 However, the recent approval by the FCC of TVBDs that use geo-location 

technology with a database demonstrates this spectrum-sharing technology could open up new 

sharing opportunities with systems operating at fixed locations (e.g., military bases, test facilities). 

Since the transmitter and receiver for a radar system are at the same location, geo-location 

technology could be effective, particularly for fixed ground-based radar systems. Geo-location 

technology may not be particularly effective for transportable ground-based radar systems or 

airborne radar systems that may be authorized to operate nationwide and shipborne radar systems 

that can operate anywhere along the U.S. coast.

To implement geo-location technology, a database of radar locations or geographic locations 

around which protection distances and/or frequency restrictions are established could be 

developed.56 Many of the same database management and authorization issues that the FCC had to 

address with the TVBDs would have to be addressed if geo-location technology is implemented to 

protect federal radar systems.57 NTIA, in conjunction with the DoD and other affected agencies, 

 54 The reciprocal of pulse repetition rate is the pulse repetition interval.

55 The IEEE 802.11ac standard that is being developed does not include provisions for geo-location technology.

56 As an interim procedure to protect Terminal Doppler Weather Radar (TDWR) systems from interference, the FCC 

requires U-NII devices within 35 kilometers of a TDWR location to be separated by at least 30 MHz from the TDWR 

operating frequency. See Federal Communications Commission Office of Engineering and Technology Laboratory 

Division Interim Plans to Approve UNII Devices Operating in the 5470 - 5725 MHz Band with Radar Detection and 

DFS Capabilities (Oct. 14, 2010) available at

http://apps.fcc.gov/kdb/GetAttachment.html?id=dV24P2kaxB%2BkKzIPZxHxHg%3D%3D. 

57 The FCC designated multiple database administrators from the private sector to create and operate the Television 

Band Devices databases. Areas addressed by the FCC related to the database included: 1) the construction of the 

database(s), including its contents; 2) sharing of information among the databases; 3) the determination of available 

channels; and 4) required security provisions. FCC Public Notice, Office of Engineering and Technology to Conduct 

Workshop for TV Bands Device Database Managers on March 10, 2011, ET Docket No. 04-186, DA 11-404 (Mar. 1, 

2011).
4-8

will examine in more detail whether geo-location spectrum-sharing technology could be used to 

mitigate the risks associated with signal sensing spectrum-sharing technologies.

Risk Element 2 - Changes in U-NII Device Deployment and Technical Parameters May Result 

in Harmful Interference

Representatives from industry provided information about U-NII device deployment and 

technical parameters that can be used in analyzing whether to introduce devices employing DFS 

sharing technology in the 5350-5470 MHz band. Appendix B provides NTIA’s assessment of these 

U-NII device deployment and technical parameters. NTIA compared the information submitted by 

the group of industry representatives to the U-NII device deployment and technical parameters used 

in developing the existing U-NII regulations in the 5250-5350 MHz and 5470-5725 MHz bands. 

The assessment shows that U-NII device deployment parameters related to the total number of UNII devices and the distribution of U-NII devices have changed from those used in the development 

of the existing regulations because U-NII technology is now incorporated in so many types of 

wireless devices.58 Accordingly, these new deployment parameters need to be considered to 

determine whether the existing U-NII regulations are appropriate or what revisions are necessary to 

implement DFS sharing technology in the 5350-5470 MHz band. The density of U-NII devices is 

one of the key parameters in determining the amount of potential interference to the incumbent 

federal systems. It will be critical, working with industry, to establish a realistic U-NII device 

density before conducting the detailed technical analysis to accurately assess the impact of

expanding access to the 5350-5470 MHz band.

The assessment of the U-NII device technical parameters indicates strong conformity with 

the industry inputs describing the distribution of U-NII device EIRP levels.59 However, the 

industry recommendation for distribution of RF channel bandwidths and recent IEEE 802.11 

amendments to U-NII device waveform modeling to cover all possible frame sizes differ from 

assumptions used in the development of the existing regulations.60 These technical parameters 

require more detailed examination to determine if the existing U-NII regulations are appropriate or 

what revisions are necessary to introduce DFS sharing technology in the 5350-5470 MHz band. 

Risk Element 3 - Existing U-NII Regulations May Not Adequately Protect Current and 

Future Radar Systems from Serious Degradation 

The sharing scenarios for ground-based and shipborne radar systems and the methodology 

contained in NTIA Technical Memorandum 09-461 will serve as the basis for performing additional

quantitative analytical studies assessing the potential impact of DFS-enabled U-NII devices to 

 58 Industry Input at 4.

59 Id. at 5.

60 Id. at 4.
4-9

federal radar systems in the 5350-5470 MHz band.61 NTIA, in conjunction with the DoD, will 

determine if the sharing scenarios and analysis methodology previously used adequately protect 

ground-based and shipborne radars operating in the 5350-5470 MHz band. The quantitative 

analysis results may show the need to modify the existing DFS regulations to adequately protect 

ground-based and shipborne radar systems operating in the 5350-5470 MHz band.

In developing the existing FCC U-NII regulations, the supporting analysis did not take into 

consideration airborne radar systems. Expanding the U-NII regulations to the 5350-5470 MHz 

band introduces a new airborne radar sharing scenario(s) that will need to be developed and 

evaluated. NTIA Technical Memorandum 09-461 described an airborne sharing scenario, but it was 

not used in the development of the detection thresholds specified in the existing FCC U-NII

regulations.

62 NTIA, in conjunction with the DoD, will determine if the sharing scenarios and 

analysis methodology previously used in establishing the U-NII regulations addresses the identified 

risks for airborne radars operating in the 5350-5470 MHz band. The quantitative analysis results 

may show the need to modify the existing regulations to adequately protect airborne radar systems 

operating in the 5350-5470 MHz band.

Risk Element 4 - Changes to U-NII DFS Detection Parameters May Not Protect Current and 

Future Radar Systems from Serious Degradation

To improve range resolution and range accuracy, some radar systems in the 5350-5470 MHz 

band employ short (sub-microsecond) pulsewidths.63 As shown in Appendix A, the smallest 

pulsewidth used in developing the existing U-NII regulations was 1 microsecond. The ability of 

signal sensing spectrum-sharing technologies to detect sub-microsecond pulses is not known at this 

time. It will be necessary to perform laboratory and field measurements to evaluate the capability to 

detect radar signals employing sub-microsecond pulses. NTIA, in conjunction with the DoD, will 

identify any changes to the existing signal parameters contained in Appendix A representing the 

radar systems operating in the 5350-5470 MHz band. To address this risk, the new waveforms will 

need to be used in laboratory testing of prototype devices. Testing with an operational radar system 

may be necessary to validate the effectiveness of any proposed changes to the U-NII regulations to 

address this risk. In addition, some recently fielded and in-development radar systems include lowpower modes or are designed to avoid detection to meet their mission requirements. This may 

require a more detailed examination of cases where spectrum sensing spectrum-sharing technology 

may not protect radar systems (e.g., radar systems designed to avoid detection).

 61 NTIA Technical Memorandum TM-09-461, Description of a Model to Compute the Aggregate Interference from 

Radio Local Area Networks Employing Dynamic Frequency Selection to Radars Operating in the 5 GHz Frequency 

Range (May 2009), available at http://www.its.bldrdoc.gov/publications/2498.aspx.

62 NTIA determined that the existing airborne radar operations could be accommodated in the 5350-5470 MHz portion 

of the band where there were no U-NII devices operating.

63 A narrow pulsewidth also improves radar detection capabilities in cluttered environments.
4-10

Risk Element 5 - Existing U-NII Regulations May Introduce “Hidden Node” Interference that 

Seriously Degrades Performance 

The current FCC regulations require only U-NII access point devices (also referred to as 

master devices) to perform the DFS channel availability check.

64 However, circumstances may 

arise where significant propagation loss differences occur between a radar system and the U-NII 

client devices operating within a network. In those cases, the assumption of a symmetrical 

propagation path between the radar system and the access point is not valid. The propagation path 

between the radar and the access point device may be obstructed, but the propagation path between 

the radar system and client devices (“hidden nodes”) is unobstructed, potentially resulting in 

excessive interference to the radar system. The conditions under which the “hidden node” 

interference problem can occur will require examination to determine whether it is necessary to 

tailor the existing U-NII regulations (e.g., incorporate DFS functionality in all U-NII devices).

Risk Element 6 - U-NII Devices Operating on an Adjacent Channel Can Cause Harmful 

Interference to Radar Systems

As part of the TDWR interference investigation, NTIA determined that, under certain 

conditions, U-NII devices operating on an adjacent channel could cause interference.65 The U-NII 

devices considered in NTIA’s investigation were located on buildings using high-gain directional 

antennas with clear line-of-sight to the TDWR. NTIA determined that the adjacent channel 

interference level was a function of frequency separation, distance separation, and antenna 

coupling.66 The analysis and measurements performed to develop the existing U-NII DFS 

regulations did not consider the effects of adjacent channel interference. This analysis assumed that 

once a U-NII DFS device detected a radar signal it moved to a channel that was separated far 

enough in frequency to eliminate adjacent channel interference. Based on the TDWR interference 

investigation NTIA determined that some devices were not moving far enough away in frequency 

and their out-of-channel emissions were causing interference to TDWR. Given the anticipated 

increase in U-NII device density, adjacent channel interference to radar systems must be taken into 

account. The methodology in NTIA Technical Memorandum 09-461 will be expanded to include 

off-frequency interference from U-NII devices for a more detailed analysis. This more detailed

analysis will consider various approaches to addressing the adjacent channel interference that can be 

included in the U-NII DFS regulations, such as establishing a minimum frequency separation or 

limits on out-of-channel emissions.

 64 See 47 C.F.R. § 15.407(h)(2)(i)(A).

65 NTIA Case Study Part III at 14.

66 Id.
4-11

Risk Element 7 – Radar Receiver Interference Protection Criteria Used to Develop Existing 

U-NII DFS Regulations May Not Adequately Address Low-Level Interference Effects

In developing the existing U-NII DFS regulations NTIA established an interference 

threshold for the radar system receivers based on an interference-to-noise ratio of -6 decibel (dB). 

NTIA determined harmful interference to radar systems can occur even when there are low levels of 

interference.67 Loss of targets at low interference levels is sometimes difficult to assess because 

there is no overt indication to the operator or even sophisticated radar software that the target losses 

are occurring. To address these low-level interference effects, it may be necessary to use more 

stringent interference protection criteria for radar receivers. As part of the quantitative study, it will 

be necessary to evaluate the interference protection criteria used in the development of the current 

DFS regulations and revise the interference protection criteria as necessary to address low-level 

interference effects.

Risk Element 8 – Channel Response Time Requirements in the Current DFS Regulations May 

Not be Adequate to Protect All Radar System Operational Scenarios

The U-NII DFS certification tests do not include a requirement for how quickly a device 

must detect a radar system. The channel move time requirement only specifies that, after a radar 

system is detected, all U-NII device transmissions are required to cease operation on the radar 

frequency channel with a move time of 10 seconds. Transmissions for normal traffic during this 

period are limited to a maximum of 200 milliseconds after detection of the radar signal. The 

feasibility of establishing specifications for U-NII channel response time, which includes the U-NII 

device listening frequency and dwell time, must be investigated. As part of the quantitative study 

the different radar system operational scenarios will need to be evaluated to determine if it is 

necessary to establish a requirement for how quickly (from the first pulse above the detection 

threshold) a U-NII device must detect the radar system. The projection of the expected stream of 

pulses over the detection threshold also needs to be evaluated in order to specify the frequency and 

dwell time requirements of the U-NII device detection window. The methodology in NTIA 

Technical Memorandum 09-461 needs to be modified to evaluate listening frequency and dwell 

time requirements and to support the revisions in Recommendation ITU-R M.1652 for the IEEE 

802.11ac data transmissions. If new listening frequency and dwell time requirements are deemed 

necessary, they would need to be incorporated into the U-NII DFS certification test procedures.

 67 Technical Report TR-06-444 at 137. 
4-12

DESCRIPTION OF RISKS TO AIRBORNE SYSTEM OPERATIONS IN THE 5350-5470 

MHZ BAND

Risk Element 1 - Current U-NII Regulations Were Not Developed to Detect Airborne Signals

Signals from ground-based and airborne transmitters were not considered in the 

development of the existing U-NII regulations because these system operations were not part of the 

previous studies for U-NII devices. To evaluate whether the existing U-NII device regulations can 

be used to detect airborne signals, representative technical parameters for ground-based and 

airborne transmitters and receivers will have to be developed, as well as sharing scenarios 

associated with UAS operations. The methodology documented in NTIA Technical Memorandum 

09-461 can serve as the basis for performing the analytical studies assessing the potential impact of 

DFS-enabled U-NII devices to federal airborne systems. The analysis of the different sharing 

scenarios will show whether DFS can be implemented to address the identified risk.

Risk Element 2 - U-NII Signal Detection Technologies May Not Be Capable of Detecting 

Airborne Signals Resulting in Serious Performance Degradation

The following paragraphs evaluate the impact on different spectrum-sharing technologies 

related to the risk associated with detecting digital airborne signals.

Energy Detection. Airborne signals employ digital formats with complex modulation schemes that 

have different spectral characteristics than the pulsed signals transmitted by radar systems used in 

the development of the existing U-NII device regulations. Since threshold detection does not 

require knowledge of the environmental signal characteristics, it could be an effective spectrumsharing technology for U-NII devices operating in the 5350-5470 MHz band. NTIA, in conjunction 

with the DoD and wireless industry representatives, will attempt to define parameters of airborne

signals so that this spectrum-sharing technology can address the identified risk.

Matched Filter Detection. Threshold detection, in conjunction with matched filter technology, is 

currently being used to improve the detection capabilities for sharing between U-NII devices 

employing digital modulation formats. The signal parameters associated with the U-NII device data 

transmissions are well defined, thereby enhancing matched filter performance. NTIA, in 

conjunction with the DoD and industry representatives, will attempt to define parameters of 

airborne signals in such a way as to use matched filter technology to improve detection capabilities 

of U-NII devices to address the identified risk.

Signal Detection. Signal detection technology, employing a combination of threshold detection 

and signal parameter pattern recognition as currently used by U-NII DFS-enabled devices operating 

in the 5250-5350 MHz and 5470-5725 MHz bands, is designed to detect pulsed radar signals 

(parameters shown in Appendix A). Digital UAS signals’ spectral characteristics differ from pulsed 

radar signals’ spectral characteristics currently detected by U-NII DFS enabled devices. NTIA, in 

conjunction with DoD and industry representatives, will determine whether they can use or adapt 

existing signal detection techniques for sharing among U-NII devices to detect ground-based and 

airborne UAS signals to address the identified risk.
4-13

Geo-Location. The FCC regulations for U-NII devices and the IEEE 802.11ac standard do not 

address geo-location spectrum-sharing technology. To implement geo-location technology, a 

database could be developed of UAS ground-based transmitter and receiver locations around which 

to establish protection distances and/or frequency restrictions. It may be possible to use frequency 

relationships between the ground-based UAS transmitters to protect airborne UAS receivers.68

Many of the same database management and authorization issues that the FCC had to address with 

TVBDs would have to be addressed if geo-location technology is implemented to protect federal 

UAS systems. NTIA, in conjunction with DoD and the industry representatives, will examine in 

more detail whether geo-location spectrum-sharing technology could be used to mitigate the risks 

associated with ability of signal sensing spectrum-sharing technologies to protect UAS operations. 

Risk Element 3 - Current U-NII Regulations Were Not Developed to Protect Systems Where 

the Transmitter and Receiver are Not Co-Located 

The existing U-NII regulations were developed specifically to protect radar receivers from 

interference where the transmitter and receiver are co-located. UAS employ ground and airborne 

transmitters and receivers located in different locations. Full duplex systems with the uplink and 

downlink on different frequencies can introduce a different “hidden node” problem.

69 A “hidden 

node” could occur when a U-NII device is signal sensing on a RF channel and the path between the 

U-NII device and a UAS ground transmitter is blocked by terrain. The U-NII device is not able to 

detect the signal from the UAS ground transmitter and would identify that RF channel as 

unoccupied and available for use. However, there could be an airborne UAS receiver operating on 

that RF channel in view of U-NII devices, resulting in potential interference to the UAS airborne 

receiver as shown in Figure 4-1.

 68 This solution may not address potential interference to mobile UAS receivers with nationwide frequency 

assignments, because to date the database method has been used for non-mobile operations, as the data is fixed and 

known, whereas data for mobile receivers is not fixed and known.

69 See Facilitating Opportunities for Flexible, Efficient, and Reliable Spectrum Use Employing Cognitive Radio 

Technologies, Notice of Proposed Rulemaking and Order, ET Docket No. 03-108, 18 F.C.C. Rcd. 26859, 26868 (2003), 

available at http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-03-322A1.pdf. 
4-14

U-NII Devices Cannot 

Detect UAS Ground 

Transmit Frequency F1

and F1 is Determined to 

be Unoccupied

Airborne UAS

Receive on Frequency F1

Transmit of Frequency F2

Ground UAS

Transmit on Frequency F1

Receive on Frequency F2

F1

Interfering Links Transmitting 

on Frequency F1 F2

F1 F1

F1

Figure 4-1. Example of “Hidden Node” Problem

Radar transmitters and receivers operate on the same frequency, whereas UAS transmitters 

and receivers operate on different frequencies. It may be possible to use frequency relationships 

between the UAS transmitters and receivers to address the “hidden node” problem. If the U-NII 

devices are able to detect the UAS airborne transmit frequency (F2 in Figure 4-1), and there is a 

known relationship between the transmitter and receiver frequencies, the U-NII devices can avoid 

transmitting on the UAS receive frequency, thereby eliminating the interference to the UAS 

receiver. If the UAS transmitter/receiver operating frequency information does not change, it could 

be provided in a look-up table or specified on a geographic basis, using a database in conjunction 

with geo-location technology. NTIA will work with DoD to determine whether the UAS 

transmitter and receiver frequency information can be made available. NTIA will also work with 

industry representatives to determine if they can implement this approach or have alternative 

solutions, such as cooperative sensing or beacons, to address the identified risk associated with the 

“hidden node” problem.

Risk Element 4 - Changes to DFS Detection Parameters May Not Protect UAS Operations 

from Serious Performance Degradation

The ability of DFS signal sensing spectrum-sharing technologies to detect digital UAS 

signals is not known at this time. It will be necessary to perform laboratory and field measurements 

to evaluate the capability of DFS to detect UAS signals. NTIA, in conjunction with the DoD, will 

develop representative test waveforms for laboratory measurements to verify DFS detection 

capabilities. To address this risk, laboratory testing of prototype devices will require new 

waveforms to represent UAS signals. Depending on the results of the laboratory measurements, 

testing with an operational UAS system may be necessary to validate the effectiveness of any 

proposed changes to the U-NII regulations to address this risk. 
4-15

DESCRIPTION OF RISKS TO SPACEBORNE SAR OPERATIONS IN THE 

5350-5470 MHZ BAND

Risk Element 1 - Existing U-NII Regulations Were Not Developed to Protect Spaceborne SAR 

Receivers

Spaceborne SAR transmitters were not considered in the development of the existing FCC 

U-NII regulations. In preparation for the 2003 World Radiocommunication Conference (WRC-03), 

Canada performed technical studies examining sharing between SAR receivers and radio local area 

network (RLAN) devices.

70 The studies performed by Canada were based on specific technical and 

deployment assumptions for the RLAN devices. NTIA will use updated deployment and technical 

information for U-NII devices in quantitative analytical studies to determine the potential 

interference impact to SAR receivers to address the identified risk. 

The studies in Recommendation ITU-R RS.1632, indicated that sharing was possible when 

certain restrictions were placed on the RLAN devices, including: indoor deployment, maximum 

EIRP of 23 dBm, TPC, and a uniform spreading of the channel loading across the band.71 An EIRP 

elevation angle mask as shown in Table 4-2 is a possible mitigation technique to improve

compatibility between RLAN devices and SAR receivers.

72 

Table 4-2. Internationally Adopted RLAN EIRP Mask

EIRP

(dBW/MHz)

θ

(Angle in degrees above the local horizontal plane of the Earth)

-13 0° ≤ θ < 8°

-13 - 0.716 (θ - 8) 8° ≤ θ < 40°

-35.9 - 1.22 (θ - 40) 40° ≤ θ ≤ 45°

-42 45° < θ

Devices operating above an EIRP of 23 dBm must comply with this EIRP elevation angle mask.

An analysis assessing potential compatibility will need to examine limitations on U-NII 

device deployment and technical parameters as well as other mitigation techniques to determine if 

they can be implemented to adequately mitigate the potential interference to SAR receivers and 

address the identified risk.

 70 Recommendation ITU-R RS.1632, Sharing in the band 5250-5350 MHz between the Earth exploration-satellite 

service (active) and wireless access systems (including radio local area networks) in the mobile service (2003).

71 Id. at 28.

72 International Telecommunication Union Final Acts World Radiocommunication Conference 2003, Resolution 229 

Use of the bands 5150-5250 MHz, 5250-5350 MHz, and 5470-5725 MHz by the mobile service for the implementation 

of wireless access systems including radio local area networks.
4-16

ADDITIONAL SAFEGUARDS TO FACILITATE SPECTRUM-SHARING 

ARRANGEMENTS

The current FCC regulations for 5250-5350 MHz and 5470-5725 MHz allow U-NII DFS 

devices to be used indoors and outdoors. This analysis, performed as part of the quantitative study, 

makes a distinction between U-NII devices that are deployed outdoors for mobile applications using 

lower EIRP levels and omni-directional antennas, and U-NII devices deployed on buildings or 

towers used for point-to-point communication applications employing higher EIRP levels and high 

gain directional antennas. Based on the industry projections, NTIA will perform analysis limiting 

the U-NII devices operating in the 5350-5470 MHz band to a maximum EIRP of 20 dBm. Since the 

current FCC U-NII regulations only require TPC to be employed for devices operating with an 

EIRP of greater than 27 dBm, NTIA will assume as part of the quantitative analysis that TPC will 

not be required for U-NII devices operating in the 5350-5470 MHz band.

73 U-NII devices used for 

point-to-point applications will not be considered because without DFS these devices are 

incompatible with radar systems (e.g., TDWR interference from point-to-point U-NII device 

applications). It is difficult to enforce rules that require U-NII devices to operate indoors; however, 

placing limitations on the EIRP reduces the operational range of the U-NII devices used for outdoor 

applications.74

Upon developing agreed upon sharing scenarios identified for radar, UAS, and SAR systems 

operating in the 5350-5470 MHz band, NTIA will perform a quantitative analysis to determine if 

these limitations on U-NII devices improve sharing with federal systems.

 73 TPC is a feature that adjusts a transmitter’s output power based on the signal level present at the receiver. As the 

signal level at the receiver rises or falls, the transmit power will decrease or increase as needed. Therefore, TPC will 

cause the U-NII device transmitter to operate at less than the maximum power when lower signal levels can provide 

acceptable service.

74 U-NII devices operating in the 5150-5250 MHz band are restricted to indoor operation to reduce any potential for 

harmful interference to co-channel mobile-satellite service operations. See 47 C.F.R. § 15.407(e). The FCC has 

established requirements for the indoor use of ultrawideband devices including the necessity to operate with a fixed 

indoor infrastructure (e.g., a transmitter that must be connected to the AC power line) and a prohibition on any fixed 

outdoor infrastructure. See 47 C.F.R. § 15.517.
5-1

SECTION 5. EVALUATION OF RISKS TO FEDERAL SYSTEMS 

OPERATING IN THE 5850-5925 MHZ BAND

INTRODUCTION

This section describes the evaluation of the risks to federal systems and the possible 

mitigation strategies associated with allowing U-NII devices to operate in the 5850-5925 MHz 

band.

OVERVIEW OF SYSTEMS OPERATING IN THE 5850-5925 MHZ BAND

In the United States, the 5650-5925 MHz band is allocated for federal radiolocation service, 

restricted to military services, on a primary basis.

75 The 5850-5925 MHz band is also allocated to 

non-federal fixed-satellite (Earth-to-space) and mobile services on a primary basis. However, the 

non-federal fixed-satellite service allocation is limited to international inter-continental systems and 

is subject to case-by-case electromagnetic compatibility analysis. 76 The non-federal mobile service 

allocation is limited to Dedicated Short Range Communications Service (DSRCS) systems 

operating in the Intelligent Transportation System radio service.

77 An overview of the federal 

systems operating in the 5850-5925 MHz band is provided below. A more detailed description of 

the DoD systems operating in this band is provided in Appendix C.

Dedicated Short Range Communications Service Systems

The Department of Transportation (DOT) has advocated for the allocation of spectrum for 

DSRCS systems to facilitate incorporating technology and advanced electronics into the nation’s 

surface transportation infrastructure.78 Although licensed by the FCC, DSRCS systems will 

enhance safety on the nation’s highways. Analyses by DOT’s National Highway Traffic Safety 

Administration (NHTSA) show DSRCS-based connected vehicle technology could potentially 

address approximately 80 percent of the crash scenarios involving non-impaired drivers. 

Specifically, NHTSA research shows that this technology could help prevent the majority of types 

of crashes that typically occur in the real world, such as crashes at intersections or while changing 

 75 See 47 C.F.R. § 2.106, Federal Government (G) footnote G2.

76 See id. at United States (US) footnote US245. There are also secondary allocations for the amateur service in the 

5650-5925 MHz band and the amateur satellite service in the 5830-5850 MHz portion of the band. 

77 See id. at Non-Federal Government footnote NG160. 

78 See Notice to the FCC of Ex Parte Meeting – WT Docket No. 1-90 and ET Docket No. 98-95, Dedicated ShortRange Communications of Intelligent Transportation Services (U.S. Department of Transportation, July 30, 2012). See

also Petition of the Intelligent Transportation Society of America for Amendment of the Commission’s Rules to Add 

Intelligent Transportation Services (ITS) as a New Mobile Service with Co-Primary Status in the 5850-5925 MHz Band 

(May 19, 1997). The Intelligent Transportation Society of America served as a Utilized Federal Advisory Committee to 

the Department of Transportation at the time of the 1997 filing, but no longer serves that function.
5-2

lanes.79 For the purpose of this study, NTIA treats DSRCS systems like a federal system in 

assessing the feasibility of allowing U-NII devices to operate in the 5850-5925 MHz band. 

Intelligent Transportation System stations operating DSRCS are authorized to operate in the 

5850-5925 MHz band.80 DSRCS systems are used to transfer data over short distances between 

roadside and mobile units, between mobile units, and between mobile and portable units to perform 

operations related to the improvement of traffic flow, traffic safety, and other intelligent 

transportation service applications in a variety of environments.81 DSRCS operations involve two 

types of devices: a Road Side Unit (RSU) and an On-Board Unit (OBU).82

The IEEE 802.11p standard is used for medium access control and physical layer application 

for the wireless connectivity using DSRCS.83 The American Society for Testing and Materials 

(ASTM) E2213 standard specifies the transmitter and receiver specifications for DSRCS RSU and 

OBU equipment as well as a channel plan.84 While the ASTM was initially intended to serve as the 

standard for DSRC operations, much of this work was moved to IEEE 802.11 to gain broader 

acceptance of the standard within the manufacturing industry. As 802.11p developed, many 

corrections and updates were implemented. Appendix D provides a detailed description of the 

DSRCS system.

Radar Systems

The radars that operate in the 5850-5925 MHz band are primarily military systems that can 

tune across the entire 5400-5900 MHz frequency range. Radars operating in this band segment can 

be either mobile or transportable and are used for surveillance and test range instrumentation. Test 

range instrumentation radars provide highly accurate position data on space launch vehicles and 

aeronautical vehicles undergoing developmental and operational testing. FCC rules require that 

 79 See NHTSA, Fact Sheet: Improving Safety and Mobility Through Connected Vehicle Technology - U.S. Department 

of Transportation Safety Pilot, available at http://www.its.dot.gov/safety_pilot/pdf/safetypilot_nhtsa_factsheet.pdf.

80 See Amendment of the Commission's Rules Regarding Dedicated Short-Range Communications Services in the 

5.850-5.925 GHz (5.9 GHz Band), Report and Order, WT Docket 01-90, FCC 03-324 (2003), available at

http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-03-324A1.pdf; Memorandum Opinion and Order, WT Docket 

No. 01-90, FCC 06-110 (2006), available at http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-06-110A1.pdf.

81 DSRCS systems support both public safety and private operations in roadside-to-vehicle and vehicle-to-vehicle 

communication environments.

82 RSUs operate at fixed locations and are authorized under Part 90 of the FCC rules. See 47 C.F.R. §90.371. OBUs 

are mobile devices located in an automobile and authorized under Part 95 of the FCC rules. See 47 C.F.R. §95.1501.

83 IEEE 802.11p, IEEE Standard for Information technology – Telecommunications and information exchange between 

systems – Local and metropolitan area networks – Specific requirements Part 11: Wireless LAN Medium Access 

Control (MAC) and Physical Layer (PHY) specifications Amendment 6: Wireless Access in Vehicular Environments 

(2010).

84 American Society for Testing and Materials, ASTM E2213-03, Standard Specification for Telecommunications and 

Information Exchange Between Roadside and Vehicle Systems – 5 GHz Band Dedicated Short Range Communications 

(DSRC) Medium Access Control (MAC) and Physical Layer (PHY) Specifications (Reapproved 2010).
5-3

DSRCS RSU stations operating within 75 kilometers of 59 radar installations be coordinated 

through NTIA.85 

In addition to the radar systems used by the DoD, several other agencies operate radar 

systems in the band. NASA uses this band for test and launch range instrumentation radars to track 

rockets, missiles, satellites, launched vehicles, and other targets. These radars provide the prime 

coverage for range safety. Range instrumentation radar transponders also operate in the band to 

enhance radar tracking of low cross section aircraft and missiles and systems under test. The 

National Oceanic and Atmospheric Administration operates radar systems in the band that are used 

on “Hurricane Hunter” aircraft. The Department of Energy operates radar systems and their 

associated transponders in the band located at four test ranges throughout the United States.

Commercial Satellite Communication Systems

The military agencies lease capacity on commercial satellite systems to satisfy their 

communication requirements. The satellite terminals transmit an uplink signal in the 5850-

6425 MHz band and receive a downlink signal in the 3700-4200 MHz band. As a result of this 

configuration, the satellite terminal receiver will not be impacted by U-NII device operations in the 

5850-5925 MHz band. However, there is potential interference problem to the receiver on-board 

the satellite. Since the military agencies only lease the service as customers, it is anticipated that 

the impact to the satellite receiver will be addressed by the FCC working with the commercial 

satellite service providers and will not be considered as part of this study. 

IDENTIFICATION OF RISKS TO SYSTEMS OPERATING IN THE 5850-5925 MHZ

BAND

The risks identified in this study reflect the potential for interference to federal systems if the 

FCC allows U-NII devices to operate in the 5850-5925 MHz band. This interference could result 

from the technical and operational characteristics of federal systems and/or the technical and 

deployment parameters of the U-NII devices. Where feasible, the federal agencies conducted 

preliminary analyses using the existing U-NII regulations and estimated deployment parameters to 

quantify the interference risks. Table 5-1 provides an overview of the risk elements and suggested 

mitigation strategies for each category of system associated with allowing U-NII device operation in 

the 5850-5925 MHz band.

 85 See 47 C.F.R. § 90.371(b).
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Table 5-1. Overview of Risk Elements and Suggested Mitigation Strategies Associated with the 5850-5925 MHz Band

System

Category Description of Risk Element Suggested Mitigation Strategy

Radar Risk Element 1 - Changes in radar signal 

parameters may impact U-NII device detection of

radar systems.

- Review radar signal parameters used in the development of existing regulations and 

assess whether U-NII device spectrum sharing technologies can be used to protect 

current and future radar systems.

Risk Element 2 - Changes in U-NII device 

deployment and technical parameters may result 

in harmful interference.

- Update U-NII device deployment and technical parameters to be used in the 

quantitative analysis.

Risk Element 3 - Existing U-NII regulations may 

not adequately protect current and future radar 

systems from serious degradation.

- Identify new sharing scenarios for radar systems. 

- Perform quantitative analysis to evaluate current DFS regulations. 

Risk Element 4 - Changes to existing U-NII DFS 

detection parameters may not protect current and 

future radar systems from serious degradation.

- Develop representative test signals for laboratory measurements to verify DFS 

detection capabilities.

- Perform laboratory measurements using prototype devices and simulated radar 

signals. 

- Perform field measurements using actual radar signals to verify laboratory 

measurements.

- Modify existing DFS regulations based on the results of quantitative analysis and 

measurements.

Risk Element 5 – Existing U-NII regulations may 

introduce “hidden node” interference.

- Examine the conditions under which “hidden node” interference exists.

- Modify U-NII device regulations as needed to resolve “hidden node” interference.

Risk Element 6 – U-NII devices operating on an 

adjacent channel may cause harmful interference 

to radar systems.

- Perform quantitative analysis to assess the impacts of adjacent channel interference.

- Perform measurements to evaluate different options for addressing adjacent channel 

interference.

- Modify existing U-NII device regulations based on the results of quantitative analysis 

and measurements.

Risk Element 7 – Radar receiver interference 

protection criteria used to develop existing 

U-NII DFS regulations may not address low-level 

interference effects.

- Evaluate the interference protection criteria used in the development of the current 

DFS regulations to determine if they adequately protect systems from interference 

effects.

- If necessary, revise the interference protection criteria to address low-level 

interference effects.

Risk Element 8 – Channel response time 

requirements in the current DFS regulations may 

not be adequate to protect all radar system 

operational scenarios. 

- Perform analysis to determine if it is necessary to add a channel response time to the 

DFS regulations to protect radar systems operating in different scenarios.

- Modify the existing U-NII DFS device certification test procedures based on the 

results of the analysis.
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Table 5-1. Overview of Risk Elements and Suggested Mitigation Strategies Associated with the 5850-5925 MHz Band (Continued)

System

Category Description of Risk Element Suggested Mitigation Strategy

DSRCS Risk Element 1 - Existing U-NII DFS 

regulations were not developed to detect 

DSRCS signals.

- Develop representative technical parameters and sharing scenarios to examine impact to 

DSRCS RSU and OBU stations including the mobile nature of RSU devices.

- Perform analysis to evaluate whether current DFS regulations protect DSRCS receivers.

Risk Element 2 - U-NII signal detection 

technologies may not be capable of detecting 

DSRCS signals.

- Determine if current signal detection techniques for sharing among U-NII devices can be 

used or adapted to detect DSRCS RSU and OBU signals.

Risk Element 3 - Current U-NII regulations 

were not developed to protect non-co-located 

transmitters and receivers.

- Examine the conditions under which a “hidden node” problem exists.

- Identify any possible sharing approaches for more detailed analysis.

Risk Element 4 - Changes to U-NII DFS 

detection parameters may not protect DSRCS 

systems from serious performance degradation.

- Develop representative test signals for laboratory measurements to verify DFS detection 

capabilities.

- Perform laboratory measurements using prototype devices and simulated DSRCS signals. 

- Perform field measurements using actual DSRCS signals to verify laboratory 

measurements.

- Modify existing DFS regulations based results of quantitative analysis and measurements.
5-6

DESCRIPTION OF RISKS TO RADAR OPERATIONS IN THE 5850-5925 MHZ BAND

Risk Element 1 - Changes in Radar Signal Parameters May Impact U-NII Device Detection of 

Radar Systems 

The following paragraphs evaluate the impact on different spectrum-sharing technologies 

related to the risk element associated with changing the signal parameters of federal radar systems.

Energy Detection. As discussed in the evaluation of the 5350-5470 MHz band, threshold detection 

does not require knowledge of the radar signal characteristics, and will minimize the risk associated 

with changes in the signal parameters that can impact the detection of ground-based radar systems 

operating in the 5850-5925 MHz band. However, recently fielded and in-development radar 

systems that include low-power modes or are designed to avoid detection to meet their mission 

requirements may present challenges for this spectrum sharing technology.

Matched Filter Detection. Matched filter detection technology, as discussed in the evaluation of 

the 5350-5470 MHz band, requires a priori knowledge of the characteristics of the radar signals 

to be effective. This spectrum-sharing technology will not address the risk associated with 

changing radar signal parameters that can impact detection of the ground-based radar systems 

operating in the 5850-5925 MHz band.

Signal Detection. Signal sensing is performed between data transmissions. Signal detection could 

be impacted by the wider bandwidth signals and higher data rates envisioned under the IEEE 

802.11ac standard. NTIA must analyze in more detail the impact that this reduction in sensing time 

will have on detecting the ground-based radar systems operating in the 5850-5925 MHz band to 

determine if this spectrum-sharing technology addresses the identified risk. In addition, recently 

fielded and in-development radar systems that include low-power modes or are designed to avoid 

detection to meet their mission requirements may present challenges for this spectrum sharing 

technology.

Geo-Location. The FCC rules specify the latitudes and longitudes of the 59 ground-based radar 

installations that must be protected from DSRCS RSU stations.86 A coordination distance of 75 

kilometers is specified around each radar installation.87 Since the transmitter and receiver for a 

radar system are at the same location, geo-location technology should be a very effective spectrumsharing technology. To implement geo-location technology, a database of the radar locations 

around which a coordination distance is established would have to be developed. NTIA will 

perform further detailed technical analysis to determine if the 75 kilometers specified in the FCC 

Rules to protect radars from DSRCS RSU is the appropriate distance to protect radars operating in 

the 5850-5925 MHz band from U-NII devices. NTIA, in conjunction with the DoD, will examine 

in more detail whether geo-location spectrum-sharing technology could mitigate the risks associated 

with signal sensing spectrum-sharing technologies in the 5850-5925 MHz band. 

 86 See 47 C.F.R. § 90.371(b).

87 Id.
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Risk Element 2 - Changes in U-NII Device Deployment and Technical Parameters May Result 

in Harmful Interference 

Industry representatives from companies that are interested in expanding unlicensed use of 

the 5 GHz band in support of IEEE 802.11ac provided information about U-NII device deployment 

and technical parameters that can be used in analyzing whether to introduce DFS sharing 

technology in the 5850-5925 MHz band. An assessment of these U-NII device deployment and 

technical parameters is provided in Appendix B. The assessment compared the information 

submitted by industry for the U-NII device deployment and technical parameters to those used in 

developing the existing U-NII regulations in the 5250-5350 MHz and 5470-5725 MHz bands. 

Based on this assessment, the total number of U-NII devices and the distribution of U-NII devices 

differ from those used in the development of the existing regulations.88 NTIA needs to examine 

these differences in more detail to determine if the existing U-NII regulations are appropriate and, if 

not, what revisions are necessary to introduce DFS sharing technology in the 5850-5925 MHz band. 

The density of U-NII devices is one of the key parameters in determining the amount of potential 

interference to the incumbent federal systems. Establishing a realistic U-NII device density before 

conducting the detailed technical analysis is critical to accurately assessing the impact of expanding 

access to the 5850-5925 MHz band to U-NII devices.

The assessment of the U-NII device technical parameters indicated strong conformity with 

the wireless industry input describing the distribution of U-NII device EIRP levels.89 However, the 

recommended distribution of RF channel bandwidths, and revisions to how the U-NII device 

waveforms are modeled to cover all possible frame sizes that are allowed by recent IEEE 802.11 

amendments differ from those used in the development of the existing regulations.90 NTIA needs to 

examine these technical parameters in more detail to determine if the existing U-NII regulations are 

appropriate or what revisions are necessary to implement DFS sharing technology in the 5850-

5925 MHz band. 

Risk Element 3 - Existing U-NII Regulations May Not Adequately Protect Current and 

Future Radar Systems from Serious Degradation

The sharing scenarios for ground-based radar systems and methodology documented in 

NTIA Technical Memorandum 09-461 serves as the basis for performing the quantitative analytical 

studies assessing the potential impact of DFS enabled U-NII devices to federal radar systems in the 

5850-5925 MHz band.91 NTIA, in conjunction with the DoD, will determine if the sharing 

scenarios and analysis methodology previously used in establishing the FCC U-NII regulations 

 88 Industry Input at 4.

89 Id. at 5.

90 Id. at 4.

91 The methodology in NTIA Technical Memorandum TM-09-461 will need to be expanded to address off-frequency 

interference from U-NII devices.
5-8

addresses the identified risks for the ground-based radar systems operating in the 5850-5925 MHz 

band for the more detailed quantitative technical analysis.

Risk Element 4 - Changes to Existing U-NII DFS Detection Parameters May Not Protect 

Current and Future Radar Systems from Serious Degradation 

NTIA Report 99-359 provides representative signal parameters (e.g., pulsewidth, pulse 

repetition interval) for radar systems operating in the 5850-5925 MHz band.92 As indicated by 

these signal parameters, some radars operating in the band employ sub-microsecond pulsewidths. 

As shown in Appendix A, the smallest pulsewidth used in the development of the existing U-NII

regulations was 1 microsecond. The narrow pulsewidths in conjunction with the higher data rates 

associated with the 802.11ac standard could have an impact on the detection of pulsed radar signals. 

The ability of signal sensing spectrum-sharing technologies to detect sub-microsecond pulses is not 

known at this time. It will be necessary to perform laboratory and field measurements to evaluate 

the capability of U-NII devices to detect radar signals employing sub-microsecond pulses. NTIA,

in conjunction with the DoD, will identify any changes to the existing signal parameters contained 

in Appendix A representing the radar systems operating in the 5850-5925 MHz band. To address 

this risk, the new waveforms will have to be used in laboratory testing of prototype devices. 

Depending on the results of the laboratory measurements, testing using an operational radar system 

may be necessary to validate the effectiveness of any proposed changes to the U-NII regulations to 

address this risk. In addition, some recently-fielded and in-development radar systems include lowpower modes or were designed to avoid detection to meet their mission requirements. This may 

require a more detailed examination of cases where spectrum sensing spectrum-sharing technology 

may not protect radar systems (e.g., radar systems designed to avoid detection).

Risk Element 5 - Existing U-NII Regulations May Introduce “Hidden Node” Interference 

The FCC currently requires only access point devices to employ DFS functionality. 

However, circumstances may arise where significant propagation loss differences occur between a 

radar system and the client devices operating within a network. In these cases, the assumption of a 

symmetrical propagation path between the radar system and the access point is not valid. In these 

instances, the propagation path between the radar and the access point device may be obstructed, 

but the propagation path between the radar system and client devices (“hidden nodes”) is 

unobstructed, potentially resulting in excessive interference to the radar system. NTIA will need to 

examine the conditions under which the “hidden node” interference problem can occur to determine 

whether it is necessary to modify the existing U-NII regulations (e.g., incorporate DFS functionality 

in all U-NII devices).

 92 NTIA Technical Report TR-99-359, Electromagnetic Compatibility Testing of a Dedicated Short-Range 

Communication (DSRC) System that Conforms to the Japanese Standard (Nov. 1998), available at

http://www.its.bldrdoc.gov/publications/2390.aspx. 
5-9

Risk Element 6 - U-NII Devices Operating on an Adjacent Channel Can Cause Harmful 

Interference to Radar Systems

As part of the TDWR interference investigation, NTIA determined that, under certain 

conditions, U-NII devices operating on an adjacent channel could cause interference.93 The U-NII 

devices considered in NTIA’s investigation were located on buildings using high-gain directional 

antennas with clear line-of-sight to the TDWR. NTIA determined that the adjacent channel 

interference level was a function of frequency separation, distance separation, and antenna 

coupling.94 The analysis was performed to develop the existing U-NII DFS regulations did not 

consider the effects of adjacent channel interference. This analysis assumed that once a U-NII DFS 

device detected a radar signal it moved to a channel that was separated far enough in frequency to 

eliminate adjacent channel interference. Based on the TDWR interference investigation NTIA

determined that some devices were not moving far enough away in frequency and their out-ofchannel emissions were causing interference to TDWR. Given the anticipated increase in U-NII 

device density adjacent channel interference to radar systems must be taken into account. The 

methodology in NTIA Technical Memorandum 09-461 will be expanded to include off-frequency 

interference from U-NII devices. The analysis will consider various approaches to addressing the 

adjacent channel interference that can be included in the U-NII DFS regulations such as establishing 

a minimum frequency separation or limits on out-of-channel emissions.

Risk Element 7 – Radar Receiver Interference Protection Criteria Used to Develop Existing 

U-NII DFS Regulations May Not Adequately Address Low-Level Interference Effects

In developing the existing U-NII DFS regulations NTIA established an interference 

threshold for the radar system receivers based on an interference-to-noise ratio of -6 dB. NTIA 

performed a study that determined harmful interference to radar systems can occur when there are 

low levels of interference.95 NTIA concluded that the loss of targets at low interference levels is 

sometimes difficult to assess because there is no overt indication to the operator or even 

sophisticated radar software that the target losses are occurring. To address these low-level 

interference effects, it may be necessary to use more stringent interference protection criteria for the 

radar receivers. As part of the quantitative study, it will be necessary to evaluate the interference 

protection criteria used in the development of the current DFS regulations and revise the 

interference protection criteria as necessary to address low-level interference effects.

Risk Element 8 – Channel Response Time Requirements in the Current DFS Regulations May 

Not be Adequate to Protect All Radar System Operational Scenarios

U-NII DFS certification tests do not include a requirement on how quickly a device must 

detect a radar system. The channel move time requirement only specifies that after a radar system 

 93 NTIA Case Study Part III at 14.

94 Id.

95 Technical Report TR-06-444. 
5-10

is detected all U-NII device transmissions are required to cease operation on the radar frequency 

channel with a move time of 10 seconds. Transmissions for normal traffic during this period are 

limited to a maximum of 200 milliseconds after detection of the radar signal. The feasibility of 

establishing specifications for U-NII channel response time, which includes the U-NII device

listening frequency and dwell time, must be investigated. As part of the quantitative study, NTIA 

will evaluate the different radar system operational scenarios to determine if it is necessary to 

establish a requirement for how quickly (from the first pulse above the detection threshold) a U-NII 

device must detect the radar system. The projection of the expected stream of pulses over the 

detection threshold also needs to be evaluated in order to specify the frequency and dwell time 

requirements of the U-NII device detection window. The methodology in NTIA Technical 

Memorandum 09-461 needs to be modified to evaluate listening frequency and dwell time 

requirements and to support the revisions in Recommendation ITU-R M.1652 for the IEEE 

802.11ac data transmissions. If new listening frequency and dwell time requirements are deemed 

necessary, they would need to be incorporated into the U-NII DFS certification test procedures.

DESCRIPTION OF RISKS TO DSRCS OPERATIONS IN THE 5850-5925 MHZ BAND

Risk Element 1 - Current U-NII Regulations Were Not Developed to Detect Digital DSRCS 

Signals

Signals from RSU (fixed) and OBU (mobile) DSRCS transmitters were not considered in 

the development of the existing U-NII regulations because there is no DSRCS in the bands 

governed by the existing U-NII regulations. To evaluate whether the existing U-NII device 

regulations can be used to detect signals from RSU and OBU stations, representative technical 

parameters will have to be developed with input from DOT and the intelligent transportation 

community. The sharing scenarios associated with DSRCS operations will also have to be 

developed, in collaboration with DOT, the transportation community and the wireless industry. The 

methodology documented in NTIA Technical Memorandum 09-461 would serve as the basis for 

performing the analytical studies assessing the potential impact of DFS enabled U-NII devices to 

DSRCS systems. An analysis of the different sharing scenarios could determine if DFS can be 

implemented to address the identified risk.

Risk Element 2 - U-NII Signal Detection Technologies May Not Be Capable of Detecting 

DSRCS Signals

The following paragraphs evaluate the impact on different spectrum-sharing technologies 

related to the risk associated with detecting digital DSRCS signals.

Energy Detection. DSCRS signals will employ digital orthogonal frequency-division multiplexing 

(OFDM), which has different spectral characteristics than the pulsed signals transmitted by radar 

systems used in the development of the existing U-NII device regulations. Since threshold 

detection does not require knowledge of the environmental signal characteristics, it could be an 

effective spectrum-sharing technology for U-NII devices operating in the 5850-5925 MHz band. 

NTIA, in conjunction with DOT and wireless and transportation industry representatives, will 
5-11

determine if the parameters of DSRCS signals can be defined in such a way as to use this spectrumsharing technology to address the identified risk.

Matched Filter Detection. Threshold detection, in conjunction with matched filter technology, is 

currently being used to improve the detection capabilities for sharing between U-NII devices 

employing digital modulation formats. The well-defined signal parameters associated with the UNII device data transmissions enhance matched filter performance. NTIA, in conjunction with 

DOT and transportation and wireless industry representatives, will determine if they can define 

parameters of DSRCS signals in such a way as to use matched filter technology to improve 

detection capabilities of U-NII devices to address the identified risk.

Signal Detection. Signal detection technology employing a combination of threshold detection and 

signal parameter pattern recognition, as currently used by U-NII DFS devices operating in the 5250-

5350 MHz and 5470-5725 MHz bands, is designed to detect pulsed radar signals (parameters shown 

in Appendix A). The digital DSRCS signals will have different spectral characteristics as compared 

to the pulsed radar signals currently being detected by U-NII DFS-enabled devices. In addition, 

DSRCS OBUs are mobile which may complicate signal detection. NTIA, in conjunction with DOT 

and industry representatives, will determine whether they can use or adapt existing signal detection 

techniques for sharing with radar systems or the techniques for sharing between U-NII devices to 

detect ground-based and airborne DSRCS signals to address the identified risk.

Geo-Location. The FCC regulations for U-NII DFS devices and the IEEE 802.11ac standard do 

not address geo-location spectrum-sharing technology. To implement geo-location technology, a 

database of DSRCS RSU transmitter and receiver locations around which protection distances 

and/or frequency restrictions are established could be developed.96 It may be possible to use 

frequency relationships between the RSU transmitters to protect mobile OBU receivers.97 Many of 

the database management and authorization issues that the FCC had to address with the TVBDs

would have to be addressed if geo-location technology is implemented to protect federal DSRCS 

systems. NTIA, in conjunction with DOT, the transportation community and wireless industry 

representatives, will need to examine in more detail whether they could use geo-location spectrumsharing technology to mitigate the risks associated with ability of signal sensing spectrum-sharing 

technologies to protect DSRCS operations.

Risk Element 3 - Current U-NII Regulations Were Not Developed to Protect Non-Co-Located 

Transmitter and Receiver

The existing U-NII regulations were developed specifically to protect radar receivers from 

interference where the transmitter and receiver are co-located. The DSRCS has RSU stations in 

fixed locations and OBU stations located on automobiles. Transmitters and receivers operating at 

different locations introduce a new sharing situation referred to as the “hidden node” problem. As 

 96 A change in the existing FCC rules may be needed in order to develop a database of DSRCS RSU transmitter and 

receiver locations.

97 There are OBU receivers associated with RSUs and OBU receivers that operate independent of an RSU.
5-12

discussed in the evaluation of the 5350-5470 MHz band, it may be possible to use known frequency 

relationships between the DSRCS RSU and OBU transmitters and receivers to address the “hidden 

node” problem. If the DSRCS RSU and OBU transmitter/receiver operating frequency information 

does not change, it could be provided in a look-up table or specified on a geographic basis using a 

database in conjunction with geo-location technology. NTIA will work with DOT, the wireless 

industry, the transportation community and the FCC to gather additional DSRCS transmitter and 

receiver frequency information. NTIA will also work with wireless and transportation industry 

representatives to determine if they are able to implement this approach or have alternative 

solutions to address the identified risk associated with the “hidden node” problem.

Risk Element 4 - Changes to U-NII DFS Detection Parameters May Not Protect Systems from 

Serious Degradation 

The ability of DFS signal sensing spectrum-sharing technologies to detect digital DSRCS 

signals is not known at this time. Laboratory and field measurements will be required to evaluate

the capability to detect DSRCS signals. NTIA, in conjunction with the DOT and other 

stakeholders, will develop representative test waveforms for laboratory measurements to verify DFS 

detection capabilities. To address this risk, the new waveforms will be used in laboratory testing of 

prototype devices. Depending on the results of the laboratory measurements, validation of the 

effectiveness of any proposed changes to the U-NII regulations may require testing with an 

operational DSRCS system to address this risk. 

ADDITIONAL SAFEGUARDS TO FACILITATE SPECTRUM-SHARING 

ARRANGEMENTS

The U-NII devices in the 5725-5825 MHz band are authorized to operate at higher EIRP 

levels, employ high-gain directional antennas, and are not required to employ DFS spectrumsharing technology (see Table 3-1). The higher EIRP levels and directional antennas are used for 

longer-range outdoor point-to-point U-NII device applications. A quantitative analysis would need 

to consider what limitations on the technical and deployment characteristics of U-NII devices, if 

any, would be required to ensure compatibility with the federal systems. This analysis would 

examine whether the identified risk to federal radar systems in the 5850-5925 MHz band and 

DSRCS systems in the 5850-5925 MHz band could be mitigated if U-NII devices were limited to 

the lower density point-to-point applications currently operating in the 5725-5825 MHz band. If 

those limitations prove necessary, they will determine the types of U-NII devices that are suitable 

for operation in this band. 

In many cases, the federal radar systems operating in the 5850-5925 MHz band are the same 

as those operating in the 5725-5825 MHz band currently authorized for U-NII devices.98 The band 

5725-5875 MHz, which overlaps the 5850-5925 MHz band, is also designated internationally for 

industrial, scientific, and medical (ISM) applications. Thus, federal radar systems operating within 

 98 Many radar systems are designed to operate across the entire 5250-5925 MHz band.
5-13

this band outside the United States and Possessions (US&P) must accept harmful interference that 

may be caused by ISM devices.

99 In addition to the ISM applications, low-powered unlicensed 

devices using digital and spread spectrum techniques are permitted in the 5725-5850 MHz band.100 

Federal radar systems operating throughout the 5725-5925 MHz band currently co-exist with lower 

density point-to-point U-NII devices as well as ISM and other unlicensed devices. A quantitative

analysis would show whether the risks to federal radar systems would be addressed by extending 

the existing 5725-5825 MHz band U-NII regulations to the 5850-5925 MHz band. The quantitative

analysis will also need to examine if additional technical constraints on U-NII devices operating in 

the 5850-5925 MHz band are necessary to protect federal radar systems.

Similar to the federal radar systems, DSRCS, ISM, and low-powered unlicensed devices 

share portions of the 5850-5925 MHz band. In addition to these systems, DSRCS systems when 

deployed would have to co-exist with high-powered pulsed radar systems that operate throughout 

the band.101 A quantitative analysis will need to examine if the risks to DSRCS systems are 

addressed by extending the existing 5725-5825 MHz band U-NII regulations to the 5850-5925 MHz 

band. An analysis will also need to examine if additional technical constraints on U-NII devices 

operating in the 5850-5925 MHz band are necessary to protect DSRCS systems. As discussed 

earlier, the IEEE 802.11p standard is used for the physical layer application for the wireless

connectivity using DSRCS. The analysis will also need to consider whether using the RF physical 

layer of the IEEE 802.11ac standard would improve sharing between U-NII devices and DSRCS 

systems.102 

 99 The ISM frequency bands are radio bands reserved internationally for the use of RF energy for industrial, scientific, 

and medical purposes other than communications. Examples of applications in these bands include radio-frequency 

process heating, microwave ovens, and medical diathermy machines. The emissions of these devices can create 

electromagnetic interference and disrupt radio communication using the same frequencies, so these devices were limited 

to certain bands of frequencies. In general, communications equipment operating in these bands must tolerate any 

interference generated by ISM equipment, and users have no regulatory protection from ISM device operation. See 47 

C.F.R. § 18.111. 

100 See 47 C.F.R. §§ 15.247.

101 The coordination zones around the radar installations specified in the FCC rules were established to protect the radar 

systems, not the DSRCS systems.

102 The RF physical layer defines the air interface used to transmit data.

6-1

SECTION 6. CONCLUSIONS

The analysis contained in this report identifies a number of risks to federal 

radiocommunication systems, spaceborne sensors operated by the United States and other countries, 

and transportation systems, associated with allowing U-NII devices to operate in the 5350-

5470 MHz and 5850-5925 MHz bands. Elements associated with these risks arise in part because of 

the underlying condition that the current U-NII DFS device regulations that are applicable in the 

bands 5250-5350 MHz and 5470-5725 MHz can be used to protect systems operating in the 5350-

5470 MHz and 5850-5925 MHz bands. The risks associated with each category of system 

summarized in Table 6-1 have been identified.

Table 6-1. Summary of Risk Elements Associated with U-NII Devices Operating 

in the 5350-5470 MHz and 5850-5925 MHz Bands

System 

Category

Frequency 

Band

(MHz)

Description of Risk Element

Radar Systems

5350-5470 

and

5850-5925

• Changes in radar signal parameters may impact U-NII device detection 

of radar systems.

• Changes in U-NII device deployment and technical parameters may

result in harmful interference.

• Existing U-NII regulations may not adequately protect current and 

future radar systems from serious degradation.

• Changes to U-NII DFS detection parameters may not protect current and 

future radar systems from serious degradation.

• Existing U-NII regulations may introduce “hidden node” interference.

• U-NII devices operating on adjacent channels may cause harmful 

interference to radar systems.

• Radar receiver interference protection criteria used to develop existing 

U-NII DFS regulations may not address low-level interference effects.

• Channel response time requirements in the current DFS regulations may 

not be adequate to protect all radar system operational scenarios.

Airborne 

Systems

5350-5470

• Existing U-NII regulations were not developed to detect airborne

signals.

• U-NII signal detection technologies may not be capable of detecting 

airborne signals resulting in serious performance degradation.

• Current U-NII DFS regulations were not developed to protect 

transmitters and receivers in different locations.

• Changes to U-NII DFS detection parameters may not protect airborne

operations from serious performance degradation.
6-2

Table 6-1. Summary of Risk Elements Associated with U-NII Devices Operating 

in the 5350-5470 MHz and 5850-5925 MHz Bands (Continued)

Synthetic 

Aperture 

Radar Systems

5350-5470 • Existing U-NII regulations were not developed to protect spaceborne 

receivers.

Dedicated Short 

Range 

Communication 

Service 

(DSRCS)

Systems

5850-5925

• Existing U-NII regulations were not developed to detect DSRCS 

signals.

• U-NII signal detection technologies may not be capable of detecting 

DSRCS signals.

• Current U-NII regulations were not developed to protect transmitters 

and receivers in different locations.

• Changes to U-NII DFS detection parameters may not protect DSRCS 

systems from serious performance degradation.

Notwithstanding the significant technical challenges surrounding the potential introduction 

of U-NII devices in these bands, NTIA concludes that further analysis is required to determine 

whether and how the risk factors can be mitigated through, for example, by the promulgation of

new safeguards in addition to the FCC’s existing requirements. Accordingly, NTIA, in 

collaboration with the federal and industry stakeholders and the FCC, will conduct quantitative

analysis of potential mitigation requirements in connection with regulatory proceedings. NTIA will

continue to collaborate with other federal agencies and industry stakeholders to further assess the 

feasibility of existing, modified, and new spectrum sharing technologies and approaches. This 

analysis will be more complex than that used to develop the existing U-NII DFS/TPC regulations, 

because the number of sharing scenarios between U-NII devices and federal systems is greater and 

the practical limitations of using existing or modified spectrum-sharing technologies to protect

different types of operations and platforms (i.e., airborne systems, spaceborne sensors, and DSRCS

devices) need to be assessed and evaluated. In addition, the interference to TDWR demonstrates the 

importance of the FCC certification and enforcement processes that must be taken into 

consideration to effectively preclude harmful interference if U-NII device operations are authorized 

in the 5350-5470 MHz and 5850-5925 MHz bands.

While the state-of-the-art of existing and proposed spectrum sharing technologies is 

advancing at a rapid pace, NTIA recognizes the importance of these bands to the federal agencies, 

international satellite-sensor data users, and the transportation industry and the potential risks of 

introducing a substantial number of new, unlicensed devices into them without proper safeguards. 

As the Tax Relief Act requires, the FCC and NTIA must determine that licensed users will be 

protected by technical solutions and that the primary mission of federal spectrum users will not be 

compromised before adopting service rules authorizing U-NII devices in the 5350-5470 MHz and 

5850-5925 MHz bands. 
6-3

SCHEDULE AND MILESTONES FOR QUANTITATIVE STUDY

International Telecommunication Union-Radiocommunication Sector (ITU-R) Joint Task 

Group (JTG) 4-5-6-7 is responsible for the broadband agenda item for the 2015 World 

Radiocommunication Conference (WRC-15).103 The domestic work contained in this report focuses 

on a qualitative evaluation of the risks associated with allowing U-NII devices access to the 5350-

5470 MHz and 5850-5925 MHz bands. The international work will be performed under the State 

Department International Telecommunication Advisory Committee (ITAC)-R.104 This work must 

be consistent with the domestic studies and will include identifying incumbent and U-NII system 

characteristics and performing more detailed quantitative studies (analysis and measurements) to 

fully address the risks identified in this study and determine under what specific conditions sharing 

may be possible. Table 6-2 provides a tentative schedule and milestones for completion of the 

quantitative evaluation. This schedule would enable timely reporting of U.S. findings to JTG 4-5-6-

7. 

Specifically, all JTG 4-5-6-7 studies must be finalized by the end of 2014 in preparation for 

WRC-15. However, because studies and regulatory activities required by the Tax Relief Act 

contemplate unlicensed operations that would be authorized only in the United States, there is a 

chance that these matters may not ultimately be on the WRC agenda. Adoption of standards in the 

ITU-R for unlicensed device operation in either the 5350-5470 MHz or 5850-5925 MHz bands 

could benefit both industry and the U.S. Government if the result adequately protects incumbent 

services and does not compromise the mission of federal spectrum users. Joint industry and 

government efforts in connection with WRC-03 led to a world-wide allocation for wireless access 

systems in other parts of the 5 GHz band, and this was vital to the successful completion of the 

FCC’s original U-NII rulemaking. 

NTIA is already working with the affected federal agencies to bring the incumbent and UNII system characteristics into the ITU-R study process and complete the analysis and 

measurements identified in this study. This approach will best position the United States for work 

in the ITU-R as other countries will inevitably bring forward studies on these bands.

 103 The JTG 4-5-6-7 has representatives from ITU-R Study Groups 4, 5, 6, and 7.

104 The general guidance for the ITAC is available at http://transition.fcc.gov/ib/sand/irb/guidance.html.
6-4

Table 6-2. Tentative Schedule and Milestones for Completing Quantitative Evaluation

Tentative 

Schedulea

Number 

of 

Months

Milestones

January 2013

to

March 2013

3

- Review existing analysis methodology documented in NTIA Technical 

Memorandum 09-461 and identify areas where modifications are necessary.

- Define technical characteristics of federal systems operating in 5350-5470 

MHz and 5850-5925 MHz bands.

- Define U-NII device deployment and technical parameters.

- Review existing sharing scenarios between federal systems and U-NII 

devices and make necessary modifications or develop new sharing scenarios.

- Perform initial analysis of limiting sharing scenarios to define modeling 

considerations for more detailed simulation analysis.

- Participate in FCC rulemaking proceeding called for in the Tax Relief Act.

April 2013

to

May 2013

2

- Validation of NTIA simulation analysis model.

- Review of NTIA simulation analysis model results for different sharing 

scenarios.

- Develop supporting material for 5 GHz international study.

- Participate in FCC rulemaking proceeding called for in the Tax Relief Act.

June 2013

to

July 2013

2

- Develop initial recommendations on suitability of the 5350-5470 MHz and 

5850-5925 MHz bands for U-NII device operations.

- Document initial analysis and modeling assumptions and sharing results.

- Participate in FCC rulemaking proceeding called for in the Tax Relief Act.

August 2013

to

October 2013

3

- Revise as necessary the analysis and modeling assumptions based on 

feedback from international meeting.

- Document the results of revised sharing studies.

- Participate in FCC rulemaking proceeding called for in the Tax Relief Act.

November 

2013

to

June 2014

8

- Revise as necessary the analysis and modeling assumptions based on 

feedback from international meeting.

- Document the results of revised sharing studies.

- Identify measurements necessary to verify U-NII DFS performance

- Perform laboratory measurements as necessary

- Perform field measurements as necessary

- Document laboratory and field measurements

- Participate in FCC rulemaking proceeding called for in the Tax Relief Act.

July 2014

to

December 2014

6 - Finalize recommendations for international study

- Finalize recommendations to the FCC

Note a: The dates in this schedule are tentative because delays can occur during the different stages of the 

review and coordination process and can impact completing the milestones. Equipment availability is beyond 

the control of NTIA and would also impact completing the milestones.
A-1

APPENDIX A

RADAR TEST WAVEFORMS

INTRODUCTION

This appendix describes the radar waveforms used by the Federal Communications 

Commission in the compliance measurement procedures for Dynamic Frequency Selection (DFS) 

tests under Part 15 Subpart E Rules required for Unlicensed-National Information Infrastructure (UNII) equipment that operates in the frequency bands 5250-5350 MHz and/or 5470-5725 MHz. 

RADAR TEST WAVEFORMS

The test waveforms used in the certification tests of U-NII DFS enabled devices were 

developed based on the technical characteristics of the existing and future radar systems operating 

in the 5 GHz frequency range. 

Table A-1 provides the short pulse radar test waveforms.

Table A-1. Short Pulse Radar Test Waveforms

Radar Type

Pulse Width

(μsec)

Pulse Repetition 

Interval

(μsec)

Number

of

Pulses

1 1 1428 18

2 1-5 150-230 23-29

3 6-10 200-500 16-18

4 11-20 200-500 12-16

Table A-2 provides the long pulse radar test waveform.

Table A-2. Long Pulse Radar Test Waveform

Radar

Type

Pulse

Width

(μsec)

Chirp

Width

(MHz)

Pulse Repetition 

Interval

(μsec)

Number

of Pulses per

Burst

Number

of Bursts

5 50-100 5-20 1000-2000 1-3 8-20

Table A-3 provides the frequency hopping radar test waveform.
A-2

Table A-3. Frequency Hopping Radar Test Waveform

Radar

Type

Pulse

Width

(μsec)

Pulse 

Repetition 

Interval

(μsec)

Pulses

Per Hop

Hopping

Rate

(kHz)

Hopping

Sequence 

Length (msec)

6 1 333 9 0.333 300
B-1

APPENDIX B 

ASSESSMENT OF UNLICENSED-NATIONAL INFORMATION 

INFRASTRUCTURE DEVICE DEPLOYMENT AND TECHNICAL 

PARAMETERS

INTRODUCTION

To determine the necessary Dynamic Frequency Selection (DFS) detection thresholds, 

NTIA developed a computer model that calculated the aggregate interference level into a radar 

system from a deployment of Unlicensed-National Information Infrastructure (U-NII) devices.105 

The computer model took into account the deployment and technical parameters associated with UNII devices and performed link budget calculations to determine the effect of U-NII devices 

employing the DFS sharing technology and the aggregate level of U-NII device signals that would 

be received by the radar systems. 

This appendix provides an assessment of the U-NII device deployment and technical 

parameters for use in evaluating the risks to federal systems operating in the 5350-5470 MHz and 

5850-5925 MHz bands. This assessment compares the U-NII device deployment and technical 

parameters used in the development of the existing FCC U-NII regulations with those inputs to this 

study provided by industry representing current and projected usage in the 5 GHz frequency bands 

authorized for U-NII devices. 

U-NII DEPLOYMENT TECHNICAL AND OPERATIONAL PARAMETERS USED IN 

DEVELOPING EXISTING REGULATIONS

The analysis used to develop the existing U-NII regulations, distributed U-NII devices over 

three regions: urban, suburban, and rural. The urban region reflected the corporate and public 

access use of U-NII devices. The suburban region reflected corporate, public access, and home UNII device use. The rural region reflected only home U-NII device use. The analysis method 

assumed that the three regions exist within concentric circles as shown in Figure B-1. 

 105 NTIA Technical Memorandum TM-09-461.
B-2

Urban

Suburban

Rural

Figure B-1. U-NII Device Deployment Regions

NTIA utilized three concentric rings to define the U-NII device deployment as shown in Table B-1.

Uniform distribution of devices in each zone was utilized throughout each volumetric zone 

including height.

Table B-1. U-NII Device Deployment Parameters

Deployment Parameter Urban zone Suburban zone Rural zone

Radius from the Center (km) 0-4 4-12 12-25

U-NII Device (%) 60 30 10

Building Height (m) 30 6 6

A total of 2,753 U-NII devices operating on a co-channel basis with a radar system at a given 

moment were utilized. All of the U-NII devices considered in the analysis were assumed to have a 

radio frequency (RF) channel bandwidth of 20 MHz.

The U-NII device power distribution in Table B-2 was utilized.

Table B-2. U-NII Device Power Distribution

Power Level 1 W 200 mW 100 mW 50 mW

U-NII Device (%) 5 25 40 30

The U-NII antenna pattern in the azimuth orientations is omnidirectional. The U-NII device 

elevation antenna pattern is described in Table B-3. 
B-3

Table B-3. U-NII Device Elevation Antenna Pattern

Elevation Angle θ

(Degrees)

Gain

(dBi)

45 < θ ≤ 90 –4

35 < θ ≤ 45 –3

0 < θ ≤ 35 0

–15 < θ ≤ 0 –1

–30 < θ ≤ –15 –4

–60 < θ ≤ –30 –6

–90 < θ ≤ –60 –5

In order for most devices to radiate with 1 Watt equivalent isotropically radiated power 

(EIRP), an antenna gain of 6 dBi will typically be required. The following antenna pattern from 

Recommendation ITU-R F.1336 was used:106

( ) max[ ( ), ( )] G θ = G1 θ G2 θ

2

3

1( ) 0 – 12 















θ

θ G θ = G





















+ 































θ

θ

G θ = G + k

– 1.5

3

2 0 ( ) – 12 10 log max ,1

0 – 0.1

3 107.6 10 G θ = ×

where:

G(θ): antenna gain (dBi)

θ: elevation angle (degrees)

k = 0.5

G0 = 6 dBi.

The methodology used to determine the probability of a radar signal being detected during 

the DFS device channel sensing time based on the radar parameters and the U-NII data 

transmissions is described in Annex 4 of Recommendation ITU-R M.1652.107 

 106 Recommendation ITU-R F.1336, Reference Radiation Patterns of Omnidirectional and Other Antennas in Point-toMultipoint Systems for Use in Sharing Studies (1997).

107 Recommendation ITU-R M.1652, Dynamic Frequency Selection (DFS) in Wireless Access Systems Including Radio 

Local Area Networks for the Purpose of Protecting the Radiodetermination Service in the 5 GHz Band (2003).
B-4

RECOMMENDATIONS FOR TECHNICAL AND DEPLOYMENT PARAMETERS 

OF U-NII DEVICES OPERATING IN THE 5350-5470 MHz AND 5850-5925 MHz 

BANDS

NTIA sought initial input from a group of industry representatives from companies that are

interested in expanding unlicensed use of the 5 GHz band in support of IEEE 802.11ac related to 

the deployment and technical parameters to be used in assessing the potential interference to federal 

systems if U-NII devices that would be operating in the 5350-5470 MHz and 5850-5925 MHz 

bands.108 

U-NII Device Deployment Parameters

The following subsections provide the methodology used by industry to determine the total 

number of U-NII device transmitters to be considered in the analysis.109

Determine population size. From ITU-R Recommendation F.1509, the radius of the total 

deployment zone is a function of total population as follows:110

β rR =αP B-1

where:

Rr : Radius of the equivalent circular area containing the total population P;

P : Total population;

α β, : Empirical factors, α = 0.035 and β = 0.44 .

NTIA defined the radius of the total deployment zone as 25 km. Solving for the total population 

results in:

ln

exp

Rr

P

α

β

          =  

 

  

B-2

Total population based on Equation B-2 is approximately 3 million.

Population split between environments. Based on latest available information, the wireless 

industry representatives selected the population split as given in Table B-3. The resulting 

population in each region is 919,000 in urban, 1.5 million in suburban, and 612,000 in rural. Within 

 108 Letter from Mary L. Brown, Director, Government Affairs, Cisco Systems, Inc. to Karl Nebbia, Associate 

Administrator, Office of Spectrum Management, NTIA (Sept. 26, 2012).

109 For U-NII devices employing multiple-input and multiple-output (MIMO) techniques, the analysis should evaluate 

total EIRP summed over all antennas.

110 Recommendation ITU-R F.1509, Technical and operational requirements that facilitate sharing between point-tomultipoint systems in the fixed service and the inter-satellite service in the band 25.25-27.5 GHz (2001).
B-5

each region, the type of deployments is split into corporate, public access, and residential. The 

RLAN aggregation model defines the places where RLANs transmit. 

Table B-3. Population Distribution

Environment

Population 

(%)

( PE )

Population (%)

( PD )

Urban 30

Corporate 35

Public Access 15

Residential 50

Suburban 50

Corporate 35

Public Access 15

Residential 50

Rural 20

Residential 100

The premise of corporate deployments is the corporate System Factor and corporate Activity 

Rate reflects that the RLANs and their transmissions are managed to meet work requirements, not 

for watching YouTube. The corporate population is the percent of population using Wi-Fi in 

corporate locations. 

The premise of public access deployments is the System Factor and Activity Rate reflect 

that the RLAN access points (AP) are older, there are more active users per AP, and the streaming 

content comes from less expensive wired Internet connection, not a gigabit Internet connection. 

The public access population is the percent of population using Wi-Fi not at home and not in a 

corporate location.

The premise of residential deployments is the small System Factor and Activity Rate reflect 

that the RLAN APs are older, there are few people in the residence, and the streaming content 

comes from a relatively less expensive wired connection compared to corporate Internet 

connections. RLANs used for work-from-home and student homework in the residential population

are included.

Market penetration of 5 GHz. Market penetration indicates the percentage of the population that 

use wireless access systems (WAS). Furthermore, the majority of current Wi-Fi usage is in 2.4 

GHz, especially in public access. New use cases will likely increase the market adoption of 5 GHz 

technology. However, a significant percentage of WAS traffic will remain at 2.4 GHz. Therefore, 

market penetration in Table B-4 is the percentage of population that use WAS in 5 GHz.
B-6

Table B-4. 5 GHz Market Penetration

Environment

Market Penetration of

5 GHz (%)

( M )

Corporate 80

Public Access 30

Residential 50

System factor. Multiple people will be covered by a single AP in a basic service set (BSS). In 

addition, each person has multiple devices, e.g., laptop, smart phone. Only one device or the AP 

will be transmitting at a given instant. The system factor parameter determines the ratio of the 

user’s devices to an access point. As seen in Table B-5, residential has a much smaller system 

factor to account for peer-to-peer connections in the home.

Table B-5. System Factor

Environment System Factor

( S )

Corporate 20

Public Access 25

Residential 5

Activity Rate. Consumers need larger bandwidth and higher data rates to support fast file transfer 

and video. However, over a large geographic area, it is highly unlikely that every BSS will 

simultaneously be engaging in these applications. Furthermore, public access systems are limited 

by their backhaul, reducing the aggregate access to the Internet. For example, while an 802.11ac 

AP may support 1 gigabits per second traffic within a local coffee shop, its 10 megabits per second 

Internet connection will significantly limit the over-the-air activity to 1 percent. Industry modeled 

residential activity at 5 percent because they expect the UNII device data rates to increase as 

affordable broadband access speeds increase. Table B-6 provides predicted activity rates.
B-7

Table B-6. Predicted Activity Rates

Environment Activity Rate (%)

( A )

Corporate 15

Public Access 5

Residential 5

Computation of active users. The number of active users (U) in each region is computed by 

Equation B-3.

1 U PP P M A E D S =⋅ ⋅ ⋅ ⋅ ⋅ B-3

The total number of active users in the geographic area is summed over the entire region. This is 

illustrated in Table B-7, with a total of 14,553 active users.111

Table B-7. Computation of Active Users

Radius 

(km)

Population 

Type Split

(%)

Population WAS Users = 

pop(market 

penetration)

BSS per region = 

(WAS users)/(system 

factor)

Total Active WAS users per 

region = (BSS per 

region)(active rate)

Urban 4 918742.7

Corporate 35 321559.9 257248 12862.4 1929.4

Public 15 137811.4 41343.4 1653.7 82.7

Residential 50 459371 229686 45937 2297

Suburban 12 1531237.8

Corporate 35 535933.2 428746.6 21437.3 3215.6

Public 15 229685.7 68905.7 2756.2 137.8

Residential 50 765618.9 382809.5 76561.9 3828.1

Rural 25 612495.1

Residential 100 612495.1 306247.6 61249.5 3062.5

Total 14,553

Distribution of active users over 5 GHz channels. If interference from adjacent channels is 

included in the sharing analysis with federal systems, it is necessary to populate the prospective 

active users across all of the available 5 GHz channels to capture the adjacent channel interference. 

Figure B-2 illustrates the IEEE 802.11ac channels in currently authorized and available U-NII and 

 111 The industry input contained an error in the residential population for the urban residential region. The number 

provided by industry was 160,780. The correct number is 459,371. This changes the number of total active users from 

13,060 to 14,553.
B-8

unlicensed bands along with the potential new channels (shown in red) that could result if 5350-

5470 MHz and 5850-5925 MHz bands are made available.

112

UNII-1: 5150-5250 MHz band

UNII-2: 5250-5350 MHz and 5470-5725 MHz band

UNII-3: 5725-5825 MHz band

Figure B-2. Distribution over 5 GHz Channels

It would be assumed that active users are uniformly distributed across all of the currently available 

channels and new channels 68-96 and 169-181. For each active user, the channel bandwidth would 

be based on the distribution in Table B-10 and a channel number would be selected with a uniform 

distribution from the available channels shown in Figure B-2.

Three Concentric Rings to Define the U-NII Device Deployment 

The metro device distribution of 50 percent suburban population and 20 percent rural 

population matches U.S. metro populations reported by the U.S. Census Bureau.113 Within each 

zone, nearly 10 percent of U-NII devices are operated outdoors near ground level, including 

operation in vehicles, or are co-located on street lighting and strand mounts above streets. A very 

small fraction of all U-NII devices are operated outdoors on rooftops or towers in point-tomultipoint or bridging configurations. The fraction of all U-NII devices is lower in the urban zone 

because there is much more fiber and microwave to buildings or near buildings than in the rural 

zone.

 112 This figure was presented in https://mentor.ieee.org/802.11/dcn/12/11-12-1159-03-00ai-masers-slaves-andclients.pptx.

113 United States Census Bureau publication http://www.census.gov/prod/2002pubs/censr-4.pdf , at 33. Furthermore, 

http://www.census.gov/geo/www/ua/2010urbanruralclass.html and 

http://www.fhwa.dot.gov/planning/census_issues/archives/metropolitan_planning/cps2k.cfm also report 20 percent rural 

population, and http://www.pbs.org/fmc/book/1population6.htm reports 50 percent suburban population.
B-9

Table B-8. U-NII Device Distribution

U-NII Device Distribution Parameters Urban 

Zone

Suburban 

Zone

Rural 

Zone

Radius from the Center 0-4 km 4-12 km 12-25 km

U-NII Device Percentage

(Indoor Operation)

27% 45% 18%

U-NII Indoor Maximum Height 30 m 6 m 6 m

U-NII Device Percentage

(Outdoor Ground Clutter; less than 12 m)

2.9% 4.8% 1.7%

U-NII Device Percentage

(Outdoor Operation; outdoor bridging)

0.1% 0.2% 0.3%

Outdoor Point-to-Multipoint bridging: 

Maximum Building/ Antenna Height

100 m 30 m 30 m

U-NII Device Technical Parameters

The U-NII device EIRP levels are provided in Table B-9. 

Table B-9. U-NII EIRP Distribution – EIRP when operating

U-NII

EIRP Level 1 W 200 mW 80 mW 50 mW 25 mW

U-NII Device Percentage

(Indoor Operation) 0% 16.9% 50.6% 13.4% 9.1%

U-NII Device Percentage

(Outdoor Ground Clutter; less than 

12m)

0% 1.7% 5.3% 1.4% 1%

U-NII Device Percentage

(Outdoor Operation; outdoor 

bridging)

0.6% 0% 0% 0% 0%

The EIRP in this table reflects what the actual transmit powers are likely to be, and that these in many cases will be 

below maximum power allowed based on adjusting the transmit power for capacity versus coverage. TPC therefore 

does not need to be separately modeled for the purposes of the analysis.

The EIRP levels and percentages in Table B-9 are derived from: 1) predictions of shipped 

devices for various devices classes; 2) expected EIRP of the device classes; 3) matching the 

percentages from the sum of the rows in Table B-8 to Table B-9; and 4) traffic mix in a Basic 

Service Set between Access Point and client.
B-10

The industry representatives have suggested that the ITU-R model (as used in the current 

NTIA aggregate interference simulation) gives a good approximation to typical antenna patterns 

and they recommend continuing to use ITU-R model.

The U-NII device bandwidths are contained Table B-10. 

Table B-10. U-NII Device Bandwidth Distribution

(Projected Bandwidth)

U-NII 

Transmitter 

Bandwidth

20 MHz 40 MHz 80 MHz

160 MHz

80 MHz and 80 MHz 

(non-contiguous)

Percentage of

U-NII Devices 10% 25% 50% 15%

The percentages in Table B-10 are based on experience from the transition from 20 MHz to 40 MHz 

channels in 802.11n.

The representative emission spectra for U-NII device bandwidths of: 20 MHz, 40 MHz, 80 

MHz, and 160 MHz (80 MHz and 80 MHz non-contiguous) are provided in Table B-11.

Table B-11. Representative Emission Spectra for U-NII Devices

Frequency Offset From RF Chanel Center Frequency

(MHz)

Emission Level

(dBr)

± BW/2-1 0

± BW/2+1 -20

± BW -28

± 3/2*BW -45

± 2*BW -52

Transmit emission mask for 20/40/80/160 MHz BW operation.

The emission levels at BW/2-1, BW/2+1, and BW are quoted from IEEE 802.11ac D2.0. The 

emission levels for 3/2*BW and 2*BW were determined by measurements from “Revision of Part 

III of U-NII to TDWR EMC Report.”114 These were further confirmed by several manufacturers as 

a reasonable representation of the emissions of IEEE 802.11ac devices.

Recommendation ITU-R M.1652 Annex 4 describes the methodology used to determine the 

probability of a radar signal being detected during the DFS device channel sensing time based on 

the radar parameters and the U-NII data transmissions. This methodology did not take into 

consideration the higher data rates envisioned by the IEEE 802.11ac standard. The industry group 

recommended a revision for Step 3 in ITU-R M.1652 Annex 4, to generalize the method to cover all 

possible frame sizes that are allowed by recent IEEE 802.11 amendments. The revision is described 

below:

 114 NTIA Case Study Part III at 8 and 9.
B-11

Revised Step 3: Create a waveform to represent WAS transmit time and listening periods 

using the values in Table B-12a, B-12b, B-12c, and B-12d. Table B-12a shows the 

Enhanced Distributed Channel Access (EDCA) categories. The chance of each access 

category occurring is shown the second column. For each access category a transmit 

opportunity (TXOP) phase is assumed where a station may transmit as many PHY-layer 

packets, up to the defined duration of the TXOP. Figure B-3 shows an example of PHYlayer packets exchanges in a TXOP. When a TXOP finishes, stations that want to access a 

channel need to go through contention procedures that would create quiet periods with 

random durations. The quiet periods for each access category are shown in the third column 

of Table B-12a. The default TXOP durations for each access category, according to IEEE 

802.11ac specification, are shown in the fourth column. Note that for access categories BE 

and BK no default value is recommended in the specification. Instead a single PHY-layer 

packet is transmitted, whose duration is obtained from Table B-12b, B-12c, and B-12d for 

each of the allowed bandwidths. The PHY-layer packet duration in Table B-12b, B-12c, and 

B-12d is an aggregation of several MAC-layer packets where each MAC-layer packet has a 

single TCP packet of size 1,500 bytes plus associated MAC-layer overhead. 

Figure B-3.115

In a TXOP, the station that owns the TXOP may send several PHY-layer packets to one or 

more stations and might seek a response, such as acknowledgment, from each station.

The WAS transmit waveform for each instance of a WAS packet transmission is created by 

randomly choosing an access category according to the distribution in the second column of 

Table B-12a. First a quiet period starts that is required by the WAS network to facilitate 

sharing of the access medium (i.e. the WAS channel) by the multiple devices using the 

network. This quiet period is available for in-service monitoring. The quiet period is 

chosen according to the third column of Table B-12a. Then single or multiple PHY-layer 

packet exchanges are followed. The duration of TXOP for access categories VO and VI are 

given in the fourth column of Table B-12a. For access categories BE and BK, a single 

PHY-layer packet, with duration given in Table B-12b, B-12c, and B-12d, is transmitted, 

where a duration is drawn uniformly from the table with appropriate bandwidth. Then 

another access category is chosen randomly in the same manner as the first, starting with 

another quiet period following with PHY-layer packet exchanges. This is repeated until the 

 115 This figure is reproduced with permission from Perahia, E. and Stacey, R., “Next Generation Wireless LANs: 

Throughput, Robustness, and Reliability in 802.11n,” Cambridge University Press (2008).
B-12

waveform has the same duration as that of a WAS device in the main beam of the antenna, 

as calculated in Step 1.

Table B-12a: EDCA access categories and associated quiet periods

(combined IFS and defer time)

EDCA 

Access 

Category

Access 

Category 

Probability

Quiet Period (us)

U(Y) is uniform distribution for 

integers 1 to Y

11ac Default 

TXOP 

duration (us)

Voice (VO) 0.1 AIFS[VO]+Backoff = 34 + U(15) x 9 1,504

Video (VI) 0.5 AIFS[VI]+Backoff = 34 + U(31) x 9 3,008

Best effort 

(BE)

0.2 AIFS[BE]+Backoff = 43 + U(1023) 

x 9

See Note

Background 

(BK)

0.2 AIFS[BK]+Backoff = 79 + U(1023) 

x 9

See Note

Note: For BE and BK access categories, one PHY-layer packet transmission is assumed after the 

associated quiet period. The PHY-layer packet duration is obtained from Table B-12b, B-12c, or B-12d. 

Table B-12b: PPDU duration in microsecond,

for bandwidth 20 MHz, and 1/2/3 spatial streams (SS)

PPDU 

Duration (us)

MCS

=0

MCS

=1

MCS

=2

MCS

=3

MCS

=4

MCS

=5

MCS

=6

MCS

=7

MCS

=8

MCS

=9

SS=1, 

BW=20MHz

5,228 4,364 2,924 2,204 1,484 1,124 1,004 908 764 692

SS=2, 

BW=20MHz

4,368 2,208 1,488 1,128 768 588 528 480 408 372

SS=3, 

BW=20MHz

2,936 1,496 1,016 776 536 416 376 344 296 272

Note: TCP packets = 1,500 bytes. Aggregated MAC-layer packets =8,191 bytes. PHY-layer packet duration 

limit=5,484 us (max allowed in 802.11ac).
B-13

Table B-12c: PPDU duration in microsecond, for bandwidth

40 MHz, and 1/2/3 spatial streams (SS)

PPDU 

Duration (us)

MCS

=0

MCS

=1

MCS

=2

MCS

=3

MCS

=4

MCS

=5

MCS

=6

MCS

=7

MCS

=8

MCS

=9

SS=1, 

BW=40MHz

4,204 2,124 1,432 1,084 736 564 508 460 392 356

SS=2, 

BW=40MHz 2,128 1,088 740 568 396 308 280 256 224 204

SS=3, 

BW=40MHz 1,444 748 520 404 288 232 208 196 172 160

Note: TCP packets=1,500 bytes. Aggregated MAC-layer packets =8,191 bytes. PHY-layer packet duration 

limit=5,484 us (max allowed in 802.11ac).

Table B-12d: PPDU duration in microsecond, for bandwidth

80 MHz, and 1/2/3 spatial streams (SS)

PPDU 

Duration (us)

MCS

=0

MCS

=1

MCS

=2

MCS

=3

MCS

=4

MCS

=5

MCS

=6

MCS

=7

MCS

=8

MCS

=9

SS=1, 

BW=80MHz

1,964 1,004 684 524 364 284 256 236 204 188

SS=2, 

BW=80MHz 1,008 528 368 288 208 168 152 144 128 120

SS=3, 

BW=80MHz 696 376 268 216 160 136 124 120 108 104

Note: TCP packets=1,500 bytes. Aggregated MAC-layer packets =8,191 bytes. PHY-layer packet duration 

limit=5,484 us (max allowed in 802.11ac).

ASSESSMENT OF U-NII DEVICE DEPLOYMENT AND TECHNICAL PARAMETERS

Assessment of U-NII Device Deployment Parameters 

The U-NII device deployment parameters that can potentially impact examining sharing 

with federal systems are the total number of U-NII devices and the distribution of U-NII devices.

In developing the existing FCC U-NII regulations, NTIA considered a total of 2,753 active 

U-NII devices in the sharing analysis. Taking into account factors such as population, 5 GHz 

market penetration, number of users per system, and activity rate, industry estimated there will be a 

total of 14,553 active 5 GHz U-NII devices. Although the number of active U-NII devices has 

increased by a factor of approximately six, this does not necessarily mean that the aggregate 

interference to federal systems will dramatically increase. If the DFS sharing technology is 

implemented properly, U-NII devices operating on the same RF channel as a federal system would 

detect the presence of a signal and change to another channel, turn off completely, or move to 

another frequency band (e.g., 2.4 GHz). However, because the number of U-NII devices has 

increased, it could take longer for U-NII devices to move from an occupied channel, increasing the 
B-14

duration of interference to federal systems. With the increased number of U-NII devices, it is not 

possible to determine whether the DFS detection thresholds in the existing FCC U-NII regulations 

are adequate to reduce the magnitude and duration of the aggregate interference to federal systems. 

It will be necessary to perform additional computer modeling to determine whether the existing UNII regulations are adequate to reduce the magnitude and duration of the potential aggregate 

interference to an acceptable level where sharing is possible with federal systems.

The U-NII device distributions used in the development of the existing DFS regulations and 

those provided by wireless industry representatives are shown in Table B-1 and Table B-7,

respectively. In comparing the distributions of U-NII devices in the three zones (urban, suburban, 

and rural), industry is projecting lower U-NII device usage in the urban zone at 27 percent, as 

compared to the 60 percent used in the development of the DFS regulations. Industry is also 

projecting 15 percent higher U-NII device usage in the suburban zone. From an analytical 

perspective, the building/antenna heights and the amount of building attenuation are the parameters 

that will vary in the different zones defining U-NII device distribution. The computer model 

assumes that radio propagation loss and any additional losses due to building attenuation would be 

reciprocal. That is, any reduction in the signal strength from a radar to a U-NII device used for 

detection of an occupied RF channel would be the same when determining the signal strength from 

a U-NII device to a radar used in the calculation of interference. For a single U-NII device to radar 

interaction this relationship can be easily determined. However, when considering aggregate 

interference to federal systems, the proposed change will impact 10,478 U-NII device-to-radar 

interactions (72 percent of the 14,553 active U-NII devices). The density of U-NII devices is one of 

the key parameters in determining the amount of potential interference to the incumbent federal 

systems. It will be critical to establish a realistic U-NII device density before conducting the 

detailed technical analysis to accurately assess the impact of expanding access to the 5350-5470 

MHz and 5850-5925 MHz bands. The impact of the changes in U-NII distributions on the DFS 

regulations that affect sharing with federal systems can only be evaluated through additional 

computer modeling.

Assessment of U-NII Device Technical Parameters 

The U-NII device technical parameters that can potentially impact examining sharing with 

federal systems are the distribution of EIRP levels, distribution of RF channel bandwidths, and 

changes to the methodology used in detecting a radar signal.

The distribution of power levels considered in developing the existing U-NII regulations is

shown in Table B-2. The distribution of EIRP levels provided by wireless industry representatives 

is shown in Table B-8. In order to convert the power levels in Table B-2 to EIRP levels, a 0 dBi 

antenna gain needs to be added to the values shown in Table B-2. As shown in Table B-2, 70 

percent of the U-NII devices had an EIRP of 100 mW (20 dBm) or less. The industry input 

suggests that 73 percent of the U-NII devices have an EIRP of 80 mW (19 dBm) or less. In general,

there is good agreement between the distribution of EIRP levels used in developing the U-NII 

regulations and those being suggested by industry.
B-15

The analysis performed to develop the existing U-NII regulations considered a single RF 

channel bandwidth of 20 MHz and assumed all of the 2,753 U-NII devices were operating cochannel with the radar system. The 20 MHz RF channel bandwidth was consistent with the IEEE 

802.11h standard. With development of the IEEE 802.11n and IEEE 802.11ac standards, the 

channel bandwidths have increased to 40 MHz, 80 MHz, and 160 MHz as shown in Figure B-2. 

The wider RF channel bandwidths introduce new issues that could impact sharing with federal 

systems. In developing the existing U-NII regulations, the analysis model developed by NTIA 

assumed that when a U-NII device detected a radar signal, it moved off of that channel and far 

enough away in frequency so that it no longer contributed to the aggregate interference. However, 

during a recent investigation of interference from outdoor higher EIRP U-NII devices to the 

Terminal Doppler Weather Radar system, NTIA determined that some U-NII devices moved off of 

the channel, but still caused interference due to the transmitter out-of-channel emission levels being 

too high.116 Wireless industry representatives provided representative emission spectra for U-NII 

devices in Table B-11 so this can be addressed in the analysis examining sharing with federal 

systems. NTIA will expand the methodology in NTIA Technical Memorandum 09-461 to include 

off-frequency interference from U-NII devices. This problem can be addressed by including a 

requirement in the U-NII regulations specifying a minimum frequency separation when a federal 

system is detected on an RF channel or specifying a transmitter emission mask. There are also 

questions regarding the DFS sensing capabilities associated with the wider bandwidth U-NII 

devices and the ability to detect off-frequency pulsed radar signals that will need to be addressed.

The computer model used to develop the existing U-NII regulations determines if the DFS 

detection threshold is exceeded for a particular U-NII device, generates a uniform random number,

and compares it to the probability of a U-NII device detecting a radar signal, which is referred to as 

the probability of coincidence (POC). The POC is based on a combination of the probability of a 

radar signal being present and the probability of the U-NII DFS detection not being blocked by the 

DFS-equipped device being in a transmit mode. The POC expresses the probability that the DFSequipped device is able to detect the radar signal when the radar signal is present. The time the 

radar signal is present is based on radar parameters such as 3 dB antenna beamwidth, antenna scan 

rate, pulsewidth, and pulse repetition interval. The time that the DFS-equipped U-NII device is 

capable of detecting a radar signal is based on the packet length and timing of the data 

transmissions. The model uses the parameters and methodology for calculating the POC described

in Recommendation ITU-R M.1652. Industry representatives have recommended a change to the 

methodology contained in Recommendation ITU-R M.1652 to generalize the methodology to cover 

all possible frame sizes that are allowed by recent IEEE 802.11 amendments. NTIA needs to 

evaluate closely, the impact that this new methodology will have on the detection of the different 

 116 As an interim procedure to protect Terminal Doppler Weather Radar (TDWR) systems from interference, the FCC 

requires U-NII devices within 35 kilometers of a TDWR location to be separated by at least 30 MHz from the TDWR 

operating frequency. See http://apps.fcc.gov/kdb/GetAttachment.html?id=dV24P2kaxB%2BkKzIPZxHxHg%3D%3D. 

This problem has only been encountered with U-NII devices used for outdoor point-to-point applications.
B-16

types of signals used by federal systems operating in the 5350-5470 MHz and 5850-5925 MHz

bands.
C-1

APPENDIX C 

DETAILED DESCRIPTION OF DEPARTMENT OF DEFENSE

5 GHZ SYSTEMS

INTRODUCTION

The Department of Defense (DoD) uses the 5350-5470 MHz and 5850-5925 MHz frequency 

bands for radar systems. The band is used for multifunction anti-air warfare radars that are part of a 

transportable, advanced ground-based air defense missile system in support of tactical operations 

and training. Additionally, the bands also support the operations of new multifunction shipboard 

radar systems operated by both the Navy and the U.S. Coast Guard. Navy radars also use this band 

for surface-search and navigation functions.

These frequency bands are part of the overall frequency range known as C-Band, a principal 

band supporting DoD range operations. The military agencies use this frequency range extensively 

for test and launch range instrumentation radars to track aircraft, rockets, missiles, satellites, 

launched vehicles, and other targets. These radars may be either fixed or transportable systems and 

are typically used as the prime coverage system for range safety. Many DoD ranges use 

transponders in this band, operated in conjunction with the range radars, on platforms undergoing 

testing. The transponders provide a high degree of tracking accuracy and are critical elements of 

range safety.

DoD also uses these frequency bands for other systems including weather radars and a new 

sense and avoid radar currently under development for large UAS platforms. There are also DoD 

communications links that are authorized to operate in these bands. These links variously support 

the operations of certain mid-altitude UAS platforms, remotely operated video targeting systems, 

and possible future wideband maritime communications systems. Finally, these bands support 

Electronic Attack/Electronic Warfare (EA/EW) capabilities.

This appendix describes most of the DoD systems operating in the 5350-5470 MHz and 

5850-5925 MHz bands.

UNITED STATES ARMY

Range and Tracking Radars

The Army requires accurate trajectory data of objects in the development and testing of 

various test objects such as missiles and rockets. The data are provided by range tracking radars 

and beacon transponders. These systems operate in the 5400-5900 MHz band. The range tracking 

radars are designed specifically to acquire and accurately track missiles (with or without beacons), 

nose cones, boosters, range assemblies, instrument packages, and debris and to provide trajectory 

data of these objects for real-time or future evaluation of performance. Target-position data from 

the radars also can be used to maintain range safety. Target tracking can be performed using either 

skin track or by the use of beacon transponders. Beacon transponders are installed on-board 

missiles and other test objects to enhance radar tracking of the test objects whenever the skin track 

signal is too weak or the tracking radar is experiencing interference. This is accomplished through 
C-2

the interrogation of the beacon by the tracking radar and a response (which is usually a stronger 

signal than the skin return) from the beacon transponder. 

Weather Radars

Weather radars are used to locate precipitation, calculate its motion, and estimate its type 

(i.e., rain, snow, hail, etc.). Modern weather radars are mostly pulse-Doppler radars, capable of 

detecting the motion of rain droplets in addition to the intensity of the precipitation. Both types of 

data can be analyzed to determine the structure of storms and their potential to cause severe 

weather. 

Unmanned Aerial System Data Links

The Army is a major developer and user of UASs and Unmanned Aircraft (UA). A UAS 

includes one or more UA and associated Ground Control Stations (GCS). Medium-altitude UA that 

use the 5350-5470 MHz band are used to provide homeland security; drug interdiction; intelligence, 

surveillance, and reconnaissance; combat search and rescue; laser target designation for precision 

strike by manned aircraft; convoy and raid over-watch; and real-time full-motion video for target 

development. Test and training for all these important missions are conducted at sites in the United 

States.

Several UAS include a C-Band (5250-5850 MHz) data link system, the Medium Altitude 

Endurance Unmanned Aerial Vehicle (UAV) Line-of-Sight Command and Video Link. Data are 

passed on two sub-bands: 5250-5475 MHz and 5625-5850 MHz. A diplexer permits full duplex 

operation. Command and control information is passed from the GCS to the UA using a Command 

Link (CL). Payload data and status information is passed from the UA to the GCS using a Return 

Link (RL). The transmitter and receiver units can be software configured to perform CL or RL 

functions; this is useful in relaying data from one UA to another. The affected UAS data link

systems utilize two CLs and two RLs. 

Use of UAs for development, training, and operations in the U.S. air space is highly 

regulated by the Federal Aviation Administration (FAA) to ensure aircraft safety of flight. As a 

result of safety-of-flight concerns, the FAA has placed a number of restrictions on U.S. UAS 

operations. 
C-3

UNITED STATES NAVY AND UNITED STATES MARINE CORPS/UNITED STATES 

COAST GUARD

Shipboard Navigation Radars

The shipboard navigation radar is a two dimensional (azimuth and range) pulsed radar set 

primarily designed for surface operations. It can also detect anti-ship missiles and low flying 

aircraft. The radar set operates in the 5450-5825 MHz range, using a coaxial magnetron as the 

transmitter output tube. The transmitter/receiver is capable of operation in several pulse width 

settings: long pulse (1.0 μs), medium pulse (0.25 μs), or short pulse (0.10 μs) modes to enhance 

radar performance for specific operational or tactical situations. Pulse Repetition Frequencies 

(PRFs) of 750, 1200 and 2400 pulses per second (pps) are used for the long, medium, and short 

pulse modes, respectively. The higher pulse repetition frequency (PRF) settings coupled with the 

shortest pulse increases the resolution of the radar return. Increased radar resolution enables the 

radar operator/observer to discern or differentiate between a single large target or two smaller 

targets in close proximity to each other. System performance is improved by the addition of a very 

narrow pulse mode (0.1 μs), providing better navigation and improved resolution of small targets at 

short ranges. Long and medium pulse (1 and 0.25 μs) modes are used in open sea for detection of 

long-range and medium-range targets. Performance is further improved by a digital video clutter 

suppressor and an interference suppressor. The shipboard navigation radar provides primary 

surface search and navigation capabilities, with limited air search capability, for the ships it is 

installed on. Other variations perform navigation, station keeping, and general surface search duties 

in addition to supporting the combat systems as shown below: 

• Primary combat mission (Anti-surface Warfare)—provides a quick reaction, 

automated target detection and track capability 

• Secondary combat mission (Anti-Air Warfare)—detects low elevation (conventional) 

threats.

The shipboard navigation radar set is installed on 105 U.S. Navy ships. It operates continuously 

during the ship’s deployment, and operations depend on the ship’s schedule and availability. 

Shipboard Multifunction Radar #1

The Navy and the U.S. Coast Guard are developing a new shipboard radar to operate on 

future surface combatants. This radar is currently operating on a limited number of ships and is 

approved for operational use by NTIA. This radar is a shipborne multimode three dimensional (3-

D) radar for surveillance and weapon assignments and is ideally suited for the light combatants 

providing excellent range for small Radar-Cross-Section (RCS) targets. This radar uses a phased 

array antenna for simultaneous detection and tracking of multiple targets and employs electronic 

stabilization to neutralize the rolling motion of the ship operating in choppy coastal waters. This 

shipboard radar provides the following modes of operation: target indication, sea skimmer, sea and 

air surveillance, extended range, long range surveillance, and gun fire support. 
C-4

The Shipboard Multifunction Radar #1 operates continuously during the ship’s deployment, 

based on the ship’s schedule and availability, performing normal littoral patrol activities, homeland 

defense, Humanitarian Assistance and/or Disaster Response (HA/DR) missions, or Fleet priority 

tasking. Similarly, the Coast Guard uses this same radar during the cutter’s deployment performing 

the following missions: defense readiness; drug interdiction/counter drug; other law enforcement; 

living marine resource; ports, waterways, and coastal security; migrant interdiction; search and 

rescue; and marine environmental protection. 

Shipboard Multifunction Radar #2

The Navy is also developing another new shipboard radar to operate on future surface 

combatants. This radar is currently operating on a limited number of ships and is approved for 

operational use by the NTIA. This radar also is a shipborne multimode 3-D radar for surveillance 

and weapon assignments and is ideally suited for the light combatants providing excellent range for 

small radar cross section targets. This radar uses a phased array antenna for simultaneous detection 

and tracking of multiple targets and employs electronic stabilization to neutralize the rolling motion 

of the ship operating in choppy coastal waters. 

Shipboard Multifunction Radar #2 functions include track-on-jam, target classification of 

both hovering and moving helicopters, navigation capabilities, target indication to weapon systems 

for precision anti-air/surface engagement, and splash spotting. It operates continuously during the 

ship’s deployment, based on the ship’s schedule and availability, performing normal littoral patrol 

activities, homeland defense, HA/DR missions, or Fleet priority tasking as required. 

Range and Tracking Radars and Transponders

The Navy requires accurate trajectory data for flight testing of various test objects such as 

aircraft, missiles, and rockets. The data are provided by range tracking radars and beacon 

transponders. These systems operate in the 5400-5900 MHz frequency band, which overlaps the 

5350-5470 and 5850-5925 MHz bands. The range tracking radars are designed specifically to 

acquire and accurately track missiles (with or without beacons), nose cones, boosters, range 

assemblies, instrument packages, and debris and to provide trajectory data of these objects for realtime or future evaluation of performance. Target-position data from the radars also can be used to 

maintain range safety. Target tracking can be performed using either skin track or by the use of 

beacon transponders. Beacon transponders are installed on-board missiles and other test objects to 

enhance radar tracking whenever the skin track signal is too weak or the tracking radar is 

experiencing interference. This is accomplished through the interrogation of the beacon by the 

tracking radar and a response (which is usually is a stronger signal than the skin return) from the 

beacon transponder. 

The Navy operates numerous test and training facilities within the United States and 

Possessions (US&P). These facilities are equipped with several different tracking radars. The 

radars and transponders may be tuned to any frequency in the 5400-5900 MHz frequency band, and 

operate at any time as test, evaluation, and training missions dictate. The range tracking radar 
C-5

transmits on a fixed frequency in the allocated frequency band to skin-track targets. If the use of a 

beacon transponder is required, the radar transmits a coded pulse group to interrogate the beacon 

transponder on the missile being tracked. The beacon receiver is tuned to the radar transmit 

frequency and the beacon transmits a return signal to the radar. 

Frequencies for the range tracking radars and beacon transponders are used during each 

missile system launch. As such, their use is dependent upon the number and frequency of missile 

flights scheduled at each test and training range. They can be used on a daily basis for test 

preparation and calibration, and are used continuously for the duration of each missile flight. 

Other Navy Systems

The Navy has additional systems that are capable of operating over the two frequency bands 

under study. However, the time available for this initial effort did not allow for a technical 

assessment of the possible impact of sharing on these operations and systems. The Navy will need 

to identify and describe these systems for the follow-on detailed analysis.

UAS Data Links. The Navy is a developer and user of UAS and UA. Medium-altitude 

UAS that use the 5350-5470 MHz band are used to provide homeland security; drug interdiction; 

intelligence, surveillance, and reconnaissance; combat search and rescue; laser target designation 

for precision strike by manned aircraft; convoy and raid over-watch; and real-time full-motion video 

for target development. Test and training for all of these important missions is conducted at sites in 

the United States.

The Medium-altitude UAS contains a C-Band (5250-5850 MHz) data link system.

117 Data 

is passed on two duplexed sub-bands, 5250-5475 MHz and 5625-5850 MHz. Command and 

control information is passed from the GCS to the UA using the CL. Payload data and status 

information are passed from the UA to the GCS using the RL. The transmitter and receiver units 

can be software configured to perform CL or RL functions; this is useful in relaying data from one 

UA to another. The UAS data link system utilizes two CLs and two RLs. 

SeaLancet Data Link Radio. SeaLancet is a tactical, wideband OFDM networked radio 

solution designed specifically to meet the demanding communications requirements of military 

tactical missions. This innovative, network-centric radio connects the maritime battlespace to the 

ground- and air-based theatre network, utilizing unique protocol and software modifications that 

deliver assured communications for long-range, high throughput, net-centric missions.

Compact size and high performance makes SeaLancet ideal for use on a wide range of 

tactical platforms in a dynamic, networked environment. The 5 GHz band is used as a command 

 117 See S. Bonter, Y. Kim, J. Timko, and T. Luu. Electromagnetic Compatibility Analysis of the Predator UAV Line-ofSight Data Link Terminal with the Communications-Electronics Environment at Indian Springs Air Force Auxiliary 

Field. JSC-PR-03-024. DoD Joint Spectrum Center. Annapolis, MD (November 2003) Distribution of this document 

is authorized to DoD Components Only; Operational Use; November 2003. Other requests for this document shall be 

referred to Air Combat Command UAV Special Mission Office (ACC/DR-UAV) or Joint Spectrum Center Acquisition 

Support Division (JSC/J8).
C-6

and control link band for unmanned aerial vehicles. Potential future use include littoral combat ship 

(LCS) mission modules; Extended Maritime Interdiction Operations; Tactical Ship-to-ship 

communications; Long Range Airborne Intelligence, Surveillance, and Reconnaissance; Pier side 

connectivity and coastal surveillance.

Multi-band Satellite Terminals. Multi-band satellite terminals are capable of operations in 

the satellite communications bands referred to as C, X, Ku, and Ka bands. The 5925-6425 MHz 

frequency range is the uplink, known as C-Band, for commercial Fixed Satellite services. DoD 

agencies, including the Navy, often lease communications capacity on commercial satellite systems 

operating at C-Band. The frequency range 5850-5925 MHz also has a primary allocation for 

commercial Fixed Satellite uplink operations; however, restrictions placed on such operations by 

footnote US245 have limited the development of services in the band and commercial satellite 

services are typically not provided. The C-Band satellite earth station receive frequencies are at 

3700-4200 MHz. The earth stations have no receive function in the frequency ranges of interest 

(5350-5470 MHz and 5850-5925 MHz). 

Weather Radars. Ground-based weather radars are used to aid flight control of aircraft or 

possibly tethered aerostats used for law enforcement. These radars are located near airfields and the 

resulting weather products are used by both the military and/or civilian airfield staff and/or the 

aerostat flight control staff. 

Electronic Attack/Electronic Warfare. The U. S. Navy performs EA/EW training and 

testing in the 5350-5470 MHz and 5850-5925 MHz bands. Training operations that include these 

frequency bands take place in the US&P and coastal waters, are intermittent and coordinated. 

UNITED STATES AIR FORCE

Range and Tracking Radars and Transponders

The U. S. Air Force (USAF) requires accurate trajectory data for flight testing of various test 

objects such as aircraft, missiles, and rockets. The data are provided by range tracking radars and 

beacon transponders. These systems operate in the 5400-5900 MHz frequency band, which 

overlaps the 5350-5470 and 5850-5925 MHz bands. The range tracking radars are designed 

specifically to acquire and accurately track missiles (with or without beacons), nose cones, boosters, 

range assemblies, instrument packages, and debris and to provide trajectory data of these objects for 

real-time or future evaluation of performance as well as for range safety of personnel and 

equipment. Use of target-position data from the radars is the prime means to maintain range safety. 

Target tracking can be performed using either skin track or by the use of beacon transponders. 

Beacon transponders are installed on-board missiles and other test objects to enhance radar tracking 

whenever the skin track signal is too weak or the tracking radar is experiencing interference. This is 

accomplished through the interrogation of the beacon by the tracking radar and a response (which is 

usually is a stronger signal than the skin return) from the beacon transponder. 

The USAF operates numerous test and training facilities within the US&P. The radars and 

transponders may be tuned to any frequency in the 5400-5900 MHz frequency band, and operate at 
C-7

any time as test, evaluation, and training missions dictate. The range tracking radar transmits on a 

fixed frequency in the allocated frequency band to skin-track targets. If the use of a beacon 

transponder is required, the radar transmits a coded pulse group to interrogate the beacon 

transponder on the missile being tracked. The beacon receiver is tuned to the radar transmit 

frequency and the beacon transmits a return signal on an offset frequency within the band to the 

radar. 

Frequencies for the range tracking radars/beacon transponders are used during each missile 

system launch, primarily for range safety. As such, their use is dependent upon the number and 

frequency of missile flights scheduled at each test and training range. They can be used on a daily 

basis for test preparation and calibration, and are used continuously for the duration of each missile 

flight.

UAS Data Links

Like the Army and Navy, the USAF is a major developer and user of UASs and UA. These 

systems may be used for surveillance and intelligence gathering and can support a variety of 

mission payloads including radars; cameras; infrared and electro-optical sensors; and electronic 

information gathering systems. Other federal agencies that have applications for a such a 

platform—for operations such as hurricane monitoring, maritime surveillance, drug interdiction, 

and wildfire monitoring—have systems in development or are considering such systems. In 

addition, the development of platforms and training of USAF UA pilots occur at several locations 

within the US&P. The versatility of the platform, the expanding applications, and the need for pilot 

training have increased the interest in sustaining these operations in the U.S. 

Airborne Sense and Avoid Radars

Use of UAs for development, training, and operations in U.S. air space is highly regulated 

by the FAA to ensure aircraft safety of flight. As a result of safety-of-flight concerns, the FAA has 

placed a number of restrictions on UAS operations. The USAF and other federal agencies are 

seeking to expand the U.S. operations of certain UA platforms while complying with the safety 

concerns of the FAA. To address these concerns, the DoD is developing both ground-based and 

airborne Sense-And-Avoid (SAA) capabilities to be used with UA operations. Of primary concern 

for the frequency ranges being considered is an unmanned sense, track, and avoid radar being 

developed by the USAF.

The USAF request for developmental spectrum certification describes the radar as a sensor 

whose output is used by an on-board autonomous SAA system on the UAS. The radar is able to 

detect and track other aircraft in its field of view to help avoid collisions. The system is a pulsed 

Doppler radar that uses linear frequency modulated pulses, comparatively low peak powers, and a 

high PRF. The system has a forward-looking, phased array antenna with a high gain and can scan 

in both the vertical and horizontal planes. The 5350-5460 MHz band is the primary frequency 

range currently being considered in the development of this radar, while 5150-5250 MHz is being 

considered as an alternate. 
C-8

Other USAF Systems

The USAF has additional systems that are capable of operating in the 5350-5470 MHz and 

5850-5925 MHz frequency bands. However, the time available for this initial effort did not allow 

for a technical assessment of the possible impact of sharing on these operations and systems. The 

USAF will need to identify and describe these systems for the follow-on detailed analysis.

Targeting Pods. The targeting pods use the 5250-5850 MHz frequency band for downlink 

and uplink communication with the Remotely Operated Video Enhanced Receiver (ROVER) family 

of systems. This communication link allows ROVER-equipped ground units to view targeting 

video and receive metadata from the pods (i.e., to see what the pilot is seeing), greatly enhancing 

weapon system effectiveness and reducing target acquisition time. Nominally, the analog downlink 

range is 25 miles, while the digital downlink range (at the lowest data rate) is 40 miles. For 

reliability and robustness these links are able to operate in frequency bands from UHF to Ku-band; 

operations at the frequencies of interest in this effort are on a not-to-interfere basis in the US&P 

since the band allocations do not support Mobile service operations on a primary, protected basis.

The targeting pods are carried on a variety of USAF and U.S. Marine Corp aircraft and are 

used domestically at USAF, Air National Guard, and Air Force Reserve training and testing 

locations. Follow-on versions of the pods are in various stages of development, and will continue to 

undergo qualification and operational testing at Edwards Air Force Base (AFB), Eglin AFB, and 

Nellis AFB during the upcoming months. 

Ground Multi-band Terminal. The USAF has frequency assignments for the Ground 

Multi-band Terminal (GMT) at the Utah Test and Training Range in Utah. GMT terminals are 

capable of operations in the satellite communications bands referred to as C, X, Ku, and Ka bands. 

The 5925-6425 MHz frequency range is the uplink for commercial Fixed Satellite services known 

as C-Band and DoD agencies, including the AF, often lease communications capacity on 

commercial satellite systems operating at C-Band. The frequency range 5850-5925 MHz also has a 

primary allocation for commercial Fixed Satellite uplink operations; however, restrictions placed on 

such operations by footnote US245 have limited the development of services in 5850-5925 MHz 

band. For the frequency range of interest, the GMT does not have operations as there are no

commercial satellite services in the band. The C-Band satellite receive frequencies are at 3700-

4200 MHz. The terminal has no receive function in the 5350-5470 MHz and 5850-5925 MHz 

bands.118 

Ground-Based Weather Radar. The ground-based weather radar is a version of the 

weather radar that Rockwell Collins produces for use on aircraft. The USAF has one frequency 

assignment for this ground-based weather radar at Fort Huachuca, AZ. The radar is used to aid in 

the flight control of a tethered aerostat at Fort Huachuca for law enforcement. The radar is located 

 118 There is a potential interference problem to the receiver on-board the satellite. Since the military agencies only lease 

the service as customers, it is anticipated that the impact to the satellite receiver will be addressed by the FCC working 

with the commercial satellite service providers and will not be considered as part of this study. 
C-9

near the airfield on Fort Huachuca and weather products are used by both the aerostat flight control 

staff and staff at the Army/civilian airfield.

Electronic Attack/Electronic Warfare. The USAF performs EA/EW training and testing 

in the 5350-5470 MHz and 5850-5925 MHz bands. Training operations that include these 

frequency bands take place in the US&P and coastal waters, are intermittent and coordinated.

Diagnostic Radar Systems. Diagnostic radar systems are being implemented to measure 

the effectiveness of aircraft low-observable (LO) materials. These systems use RCS imaging 

technology to identify LO defects, categorize the magnitude of the defect, and verify LO integrity 

across a broad range of frequencies, including both of the target 5 GHz bands. These diagnostic 

radar systems are used at short distances from the aircraft. Frequency assignments are in place at 

Whiteman AFB; Plant 42, Palmdale, California; Edwards AFB; Tyndall AFB; Holloman AFB; 

Nellis AFB; Hill AFB; Eglin AFB; and Langley AFB.

D-1

APPENDIX D

DESCRIPTION OF DEDICATED SHORT-RANGE COMMUNICATION 

SERVICE SYSTEMS OPERATING IN THE 5850-5925 MHZ BAND

INTRODUCTION

The appendix provides a description and technical parameters for the Intelligent 

Transportation System Dedicated Short-Range Communications Service (DSRCS) systems

operating in the 5850-5925 MHz band.

DSRCS SYSTEM DESCRIPTION

The DSRCS Road Side Units (RSUs) are authorized under Part 90 (Section 90.7) of the 

Federal Communications Commission (FCC) rules. The On-Board Units (OBUs) are authorized 

under Part 95 (Subpart L) of the FCC rules. The information in this appendix comes from the 

Institute of Electrical and Electronics Engineers (IEEE) Standard for Information technology –

Telecommunications and information exchange between systems – Local and metropolitan area 

networks – Specific requirements, Part 11: Wireless Local Area Network (LAN) Medium Access 

Control (MAC) and Physical Layer (PHY) Specifications and will be referred to as the IEEE 

802.11p standard. Other information is contained in the rules and regulations set forth by the 

Federal Communications Commission.

The modulation used for DSRCS is OFDM. Figure D-1 provides a simple block diagram 

for a transmitter and receiver.

Figure D-1. DSRCS Transmitter and Receiver
D-2

The transmitter and receiver technical characteristics for DSRCS systems are provided in 

Table D-1 through D-4.

Table D-1. Transmitter Characteristics

Parameter Value

Emission 3 dB Bandwidth (MHz) 10 or 20

Power (Peak) (dBm) 23 to 44.8 (Depending on RSU or OBU and 

Channel used)

Emission Spectrum

(Relative Attenuation (dB) as a Function of Frequency 

Offset from Center Frequency (ΔF) (MHz))

Attenuation ΔF

See Note a See Note a

Antenna Gain (Main beam) (dBi) 3 to 15 typical

Azimuth Off-Axis Antenna Pattern 

(dBi as a function of off-axis angle in degrees) 

Omni is typical; sectorized antennas sometimes 

used with 65 to 90 deg at 3dB for Infrastructure 

DSRCS transmitter antennas

Elevation Off-Axis Antenna Pattern 

(dBi as a function of off-axis angle in degrees)

Typical 3 to 15 dB with 3dB point at 15 to 35 deg.

Antenna Height (meters) 1.5-15b

Antenna Polarization Primarily vertical (some dual linear polarized)

Antenna Azimuth 3 dB Beamwidth (degrees) Normally Omni for infrastructure and vehicle; 

Infrastructure Sectorized antennas man be 65 to 90 

deg 

Cable, Insertion, or Other Losses (dB) 1 to 3 dB typical. (Function of installation and 

materials used)

Note a: Spectrum mask for 10 MHz channels, the transmitted spectral density shall have a 0 dBr bandwidth not exceeding 9 

MHz and shall not exceed the spectrum mask created using the permitted power spectral density levels listed in Table D-2.

Note b: A RSU may employ an antenna with a height exceeding 8 meters but not exceeding 15 meters provided the EIRP 

specified in the table below is reduced by a factor of 20 log(Ht/8) in dB where Ht is the height of the radiation center of the 

antenna in meters above the roadway bed surface. The EIRP is measured as the maximum EIRP toward the horizon or 

horizontal, whichever is greater, of the gain associated with the main or center of the transmission beam. The RSU antenna 

height shall not exceed 15 meters above the roadway bed surface.
D-3

Table D-2. Transmitter Power Spectral Density

Transmit

Power Class

Permitted Power Spectral Density (dBr)

± 4.5 MHz

offset (±f1)

± 5.0 MHz

offset (±f2)

± 5.5 MHz

offset (±f3)

± 10 MHz

offset (±f4)

± 15 MHz

offset (±f5)

Class A 0 –10 –20 –28 –40

Class B 0 –16 –20 –28 –40

Class C 0 –26 –32 –40 –50

Class D 0 –35 –45 –55 –65

Table D-3. Receiver Characteristics

Parameter Value

Receiver 3 dB Intermediate Frequency (IF) Bandwidth 

(MHz)

Not Applicable to OFDM Receiver; direct 

conversion to baseband

Receiver IF Selectivity

(Relative Attenuation (dB) as a Function of Frequency 

Offset (MHz))

Attenuation ΔF

See Table D-4 See Table D-4

Noise Figure (dB) 5 to 15 ; 10 typical

Antenna Gain (Main beam) (dBi) 3 to 15 typical

Azimuth Off-Axis Antenna Pattern

(dBi as a function of off-axis angle in degrees)

Omni is typical; sectorized antennas sometimes used 

with 65 to 90 deg at 3dB for Infrastructure DSRCS

transmitter antennas

Elevation Off-Axis Antenna Pattern

(dB as a function of off-axis angle in degrees)

Typical 3 to 15 dB gain with 3dB point at 15 to 35 

deg.

Antenna Polarization Typically Vertical; some dual linear

Antenna Height (meters) 1.5 to 15

Antenna Azimuth 3 dB Beamwidth (degrees) Typically omni; may be 65 to 90 deg at 3dB for 

infrastructure sectorized antenna

Cable, Insertion, or Other Losses (dB)

Function of installation, transmission cable 

type/length and connector/coupler loss; typically 1 to 

3 dB; typical value is 2 dB
D-4

Table D-4. Receiver Selectivity

Data Rate

(Megabits Per Second)

Adjacent Channel Rejection 

(dB)

Alternate Adjacent Channel 

Rejection (dB)

3 28 42

4.5 27 41

6 25 39

9 23 37

12 20 34

18 16 30

24 12 26

27 11 25
E-1

APPENDIX E

ACRONYMS AND ABBREVIATIONS

A Activity Rate

AFB Air Force Base

AIFS Arbitration Innerframe Space

AP Access Point

ASTM American Society for Testing and Materials

BE Best effort

BK Background

BSS Basic Service Set

BW Bandwidth

C.F.R. Code of Federal Regulations

CL Command Link

dB Decibel

dBi Decibel Isotropic

dBm Power ratio in decibels of the measured power to one milliwatt

dBr Decibel reference

DFS Dynamic Frequency Selection

DoD Department of Defense

DOT Department of Transportation

DSRCS Dedicated Short Range Communication Service

EA/EW Electronic Attack/Electronic Warfare

EDCA Enhanced Distributed Channel Access

EIRP Equivalent Isotropically Radiated Power

EMC Electromagnetic Compatibility

FAA Federal Aviation Administration

FCC Federal Communications Commission

GCS Ground Control Station

GHz Gigahertz

GMT Ground Multi-band Terminal

HA/DR Humanitarian Assistance and/or Disaster Response

Ht Height

IEEE Institute for Electrical and Electronics Engineers

IF Intermediate Frequency

IFS Innerframe Space

ISM Industrial, Scientific and Medical

ITU-R International Telecommunication Union-Radiocommunication Sector

JTG Joint Task Group

kHz Kilohertz

km Kilometers

LAN Local Area Network

LO low-observable

M Market Penetration

m Meters

MAC Medium Access Control Layer

MCS Modulation, coding, and spatial streams

MHz Megahertz

msec Microsecond
E-2

mW Milliwatts

NASA National Aeronautics and Space Administration

NHTSA National Highway Traffic Safety Administration

NTIA National Telecommunications and Information Administration

OBU Onboard Unit

OFDM Orthogonal Frequency Division Multiplexing

P Total Population

PE Population Environment

PD Population Distribution

PDF Probability Density Function

PHY Physical Machine Layer

PLCP Physical Layer Conversion Protocol

PPDU PLCP Protocol Data Unit

PPS Pulses per Second

PRF Pulse Repetition Frequency

POC Probability of Coincidence

PSK Phased Shift Keying

QAM Quadrature Amplitude Modulation

RADARSAT Radar Satellite

RCS Radar-Cross-Section

RF Radio Frequency

RL Return Link

RLAN Radio Local Area Network

ROVER Remotely Operated Video Enhanced Receiver

RSU Road Side Unit

S System Factor

SAA Sense-And-Avoid

SAR Synthetic Aperture Radar

SS Spatial Streams

TCP Transmission Control Protocol

TDWR Terminal Doppler Weather Radar

TPC Transmitter Power Control

TVBD Television Band Device

TXOP Transmit Opportunity

UA Unmanned Aircraft

UAS Unmanned Aircraft Systems

UAV Unmanned Aerial Vehicle

U-NII Unlicensed-National Information Infrastructure

U Uniform

U Users

U.S. United States

US&P United States and Possessions

μsec Microsecond

VI Video

VO Voice

W Watt

WAS Wireless Access Systems

Wi-Fi Wireless-Fidelity

WRC-03 World Radiocommunication Conference 2003

WRC-15 World Radiocommunication Conference 2015