GPS/GNSS
What is it?
How Does it Work?
What are its Applications?

Historic Navigation• Reference points in the sky used for navigation– The Sun
– The Pole Star / North Star
– Southern Cross• Gives Direction, but not position• Add a sextant to give latitude• And a clock to give longitude

GNSS Principles• GNSS satellites in the sky are the new reference
points• If my GNSS receiver "sees" 4 or more satellites,
it can compute my position– "see" means track and process navigation signals

Satellites as Accurate Reference Points• GNSS signals contain information about thesatellites' positions– very accurate reference points• Measure the distance from the satellites to thereceiver• Knowing at least
three distancesfrom threereference points
gives position

How do you measure distance?
speed = distance / time distance = speed x time

radio waves travel
at light speed "c"– 300,000km in 1 second– 300km in 1ms (1/1000th)– 300m in 1μs (1/millionth)– 300mm in 1ns

satellite signals
contain 'time stamps'
time = tsent – treceived

Compute position
distance = speed x time• speed = 3x108 m/s• time = tsent – treceived• but, receiver time notaccurately known• so the time stamp from afourth satellite ismeasured• compensates for the
missing receiver time

Example GNSS Signal• radio frequency at "L-band"– typically 1575MHz• at satellite: signal energy
spread by a code
• at receiver: spread signal
energy is unlocked andrefocused– "code gain"• allows simple antennas toreceive low power signals• and to share the frequency
with other satellites/systems

Position relative to?
• A position is pointless without having a groundreference• A world reference is used, eg WGS84– World Geodetic System 1984

• Allows position fix to be placed on a World grid
• Maps can be referenced to the same grid
• you can determine where you are on a map

What is GNSS used for?
PNT
• Positioning… surveying and mapping– location based services– air traffic management– search and rescue• Navigation… a given. cars, ships, cranes– remember GNSS gives position, you still needreliable/up-to-date maps and routing software• Timing?... most large networks synchronised– telecoms– electricity distribution– banking… microseconds matter for transactions!

What about?
• Monitoring sea/lake/snow levels– uses GNSS reflections seen into a fixed receiver• Atmospheric measurements– GNSS signals change as they pass throughatmosphere: air quality, gaseous content, etc• Space weather monitoring– measuring changes in the ionosphere• Soil and vegetation moisture measurements• Volcanic plume density measurements– atmospheric ash uncertainty after eruptions• Sea surface roughness, wind direction and more
• Earthquake/tsunami monitoring….
etc, etc……

Thank You
Questions?

17

GNSS History

1Satellite Navigation in the 1950s
1950

1951

1952

1953

1954

1955

4 Oct 1957
Sputnik I
Launched

1956

1957

1958

1959

Dec 1958
The U.S.
Navy
Navigation
Satellite
System(Transit)
Approved
andFunded2Satellite Navigation in the 1960s (1 of 3)
1960

1961

1962

1963

1964

1965

13 April 1960
Jan 1964
First Successful 5 Dec 1963
First
TransitTransit
BecameExperimental Operational
Satellite
Operational
Satellite (1B)

1966

1967

1968

Other Successful
Experimental
Satellites:
2A, 22 Jun 1960
3B, 21 Feb 1961
4A, 29 Jun 1961
4B, 15 Nov 1961

1969

July 1967
Transit
ReleasedforCommercial
Use---Establishing
U.S. Dual
Use SatNav
PolicyOperational
TransitSatellite
3

Satellite Navigation in the 1960s (2 of 3)
1960

1961

1962

1963

1964
World’s First Surface Ship
Satellite Navigator
AN/SRN-9 (XN-5)

1964

1965

1966

1967

1968
World’s First
Portable Satellite
Doppler Geodetic
Surveyor
AN/PRR-14
Geoceiver

1968

1969

1969
World’s First
Commercial
Oceanographic
Navigator
4Satellite Navigation in the 1960s (3 of 3)
1960

1961

1962

1963

1964

1965

1966

1967

1968

1969

1969
First Steps Toward GPS;Air Force 621B Program;
World’s First Spread Spectrum
Navigation Receiver, MX-450

5

Satellite Navigation in the 1970s
1970

1971

1972

1973

1974

1975

April 1973
Formation of the GPS
Joint Program Office
(JPO)

1971
First Timation Receiver
for the Naval Research
Lab (NRL)

1976

1977

1978

1979

1978 GPS Launches
22 Feb, 13 May,
7 Oct, 11 Dec

1975
First Concept Validation GPS
Navigator, the GPS X-Set
6

Original

7

GPS Launch Plans

National policy wasto launch all
operational GPS
satellites with thespace shuttle
The Atlas Booster launched
all Block I GPS Satellites

The January 28, 1986 Challenger
disaster forced a change
8Satellite Navigation in the 1980s
1980

1981

1982

1983

1984

1985

9 Oct ‘85
Last Block I
Launch1984
Commercial 5
Channel GPS
Navigator

1985
GPS + Transit + Omega

1986

28 Jan ‘86
Challenger
Disaster

1986
6 Channel GPS
Navigator

1987

1988

1989

14 Feb ‘89
Launches
Resume1986
WM101 GPS Satellite
Surveying Set

9GPS Selective Availability, IOC, and FOC
32
30

Number of Operational GPS Satellites

28
26
24
22
20

9/10/2008
07/04/91– SA turned on
12/08/93 – IOC Declared
04/27/95 – FOC Declared
05/01/00 – SA turned off
09/18/07 – SA Ended

18
16
14
12
10
8
6
4
2
0

FOC

IOC
SA On
78

01/01/78

82

01/01/82

86

01/01/86

90

01/01/90

SA Off SA End
94

01/01/94

98

01/01/98

02

01/01/02

06

01/01/06

08

10

Satellite Navigation in the 1990s
1990

1991

1992

4 Apr ‘91
SA Turned
On

1993

1994

8 Dec ‘93
GPS IOC

1995

1996

1997

1998

1999

27 Apr ‘95
GPS FOC1996 Professional
Marine DGPSNavigator

1991 6 Channel
GPS Engine
1990
GPS/GLONASSNavigator

26 Dec ‘91
Dissolution of
the Soviet
Union Enacted

1991 Compact
GPS Surveyor

1997 Machine
Control, 10 Hz,
30 ms, 1 cm
11

Modernization and GNSS Initiatives
32
30

Number of Operational GPS Satellites

28
26
24
22
20
18
16

9/10/2008
03/30/98– Announce Civil L2
01/25/99 – Announce Civil L505/01/00 – SA set to zero
05/26/02 – Galileo Approved
06/26/04 – U.S./EU Agreement
04/10/07 – GLONASS Memo
07/26/07 – MBOC Agreement
04/08/08 – GLONASS CDMAGLONASSCDMAGLONASS
Memo

14
12

SA
Off

10

EU-US

8

MBOC

6

L2C

4

GalileoL52078
01/01/78

82

01/01/82

86

01/01/86

90

01/01/90

94

01/01/94

98

01/01/98

02

01/01/02

06

01/01/06

08

12

Satellite Navigation in the 2000s
2000

1 May ‘00
SA set to
zero

2001

2002

2003

26 May ‘02
Galileo
Approved

2004

2005

2006

26 Jun ‘04
U.S./EU
Agreement
10 Apr ‘07
GPS/GLONASS
Cooperation
Memo

November 2004,
Qualcomm announced
successful tests of assisted
GPS for mobile phones.

2007

2008

2009

18 Sep ‘07
SA Ended

26 Sep ‘05
IIR-M
Launchwith L2C

8 Apr ‘08
GLONASSCDMA
Announced

1-2 Dec ‘05
ICG-1
Vienna13

Satellite Navigation in the 2010s
2010

2011

2012

2013

2014

2015

2016

2017

•

28 May ‘10
IIF Launchwith L5

11 Sep ‘10
QZSS
Launch6-11 Nov ‘16
ICG-11
Sochi, Russia

2019

Approaching a new
GNSS Golden Era– Many more satellites(GPS, Galileo, BeiDou,
QZSS) with L1 and L5
interoperable signals– Much better
availability, accuracy,
integrity, e.g., enabling
ARAIM

21 Oct ‘11
Operational
Galileo
Launch
2-6 Oct ‘15
ICG-10Boulder, CO

2018

•

Anticipating CDMAsignals from GLONASS•

What does the futurehold?

2-7 Dec ‘17
ICG-12
Kyoto, Japan14

Who Anticipated GPS in Cell Phones?
• Sparked by theE911 requirement• Use of Location
Based Services(LBS) is exploding• Improved byAssisted GPS(A-GPS)

More than a Billion Cell Phone GPS Users– Better accuracy– Location inseconds– Turn-by-turnnavigation

15

Who Anticipated Precision Agriculture?
• One to 10 cm accuracy• Far better productivity,
efficiency, and protectionof the environment• Enabled, e.g., by MSS
signals for the John Deere
StarFire Service andseveral others

Automatic Steering
Automatic Spray Control

16

Thank You
Questions?

17GPS Program
StatusFuture Plans
Augmentations
Applications

GNSS: A Global Navigation Satellite
System of Systems• Global Constellations– GPS (24+3)– GLONASS (24+)– GALILEO (24+3)– BDS/BEIDOU (27+3 IGSO + 5 GEO)• Regional
Constellations– QZSS (4+3)– IRNSS/NAVIC (7)• Satellite-Based
Augmentations– WAAS (3)– MSAS (2)– EGNOS (3)– GAGAN (3)– SDCM (3)– BDSBAS (3)– KASS (2)2GPS Economic Benefits Assessment(2013 -- U.S. Only)
Application

Range ofBenefits ($B)

Mid-Range
Benefits ($B)

Precision agriculture: grain

10.0–17.7

13.7

Construction: earthmoving w/ machine
guidance

2.2–7.7

5.0

Surveying

9.8–13.4

11.6

Air transportation

0.119–0.168

0.144

Rail transportation: positive train control

0.010–0.100

0.055

Maritime transportation: private sector use ofnautical charts and related information

0.106–0.263

0.185

Road: fleet vehicle connected telematics

7.6–16.3

11.9

Road: consumer and other non-fleet vehicles

7.3–18.9

13.1

Timing0.025–0.063

0.044

TOTAL

37.1–74.5

55.7
3

U.S. National Space Policy
Space-Based PNT Guideline: Maintain leadership in
the service, provision, and use of GNSS
• Provide civil GPS services, free of direct user
charges– Available on a continuous, worldwide basis– Maintain constellation consistent with published performancestandards and interface specifications– Foreign PNT services may be used to complement services fromGPS

• Encourage global compatibility and interoperability
with GPS• Promote transparency in civil service provision• Enable market access to industry• Support international activities to detect and mitigate
harmful interference

4GPS Constellation Status
35 Total Satellites / 31 Operational (Set Healthy)(Baseline Constellation: 24)
Four Generations of Operational Satellites• Block IIA - 3 Residual– 7.5 year design life
– Launched 1990 to 1997

• Block IIR - 12 Operational– 7.5 year design life (oldest operational satellite is 19
years old)
– Launched 1997 to 2004

• Block IIR-M - 7 Operational, 1 Residual– 7.5 year design life
– Launched 2005 to 2009
– Added 2nd civil navigation signal (L2C)• Block IIF - 12 Operational– 12 year design life
– Launched 2010 to 2016
– Added 3rd civil navigation signal (L5)5GPS III: Newest Block of GPS
Satellites– 4 civil signals: L1 C/A, L1C, L2C, L5– First satellites to broadcast common L1C
signal– 4 military signals: L1/L2 P(Y), L1/L2M– 3 improved Rubidium atomic clocks– Better User Range Error than IIF
Satellites– Increased availability– Increased integrity– 15 year design life

First GPS III Launch Expected Later in 20186

GPS Ground Segment• Current Operational Control Segment (OCS)– Flying GPS constellation using Architecture Evolution Plan
(AEP) and Launch and Early Orbit, Anomaly, and Disposal
Operations (LADO) software capabilities– Increasing Cyber security enhancements• Next Generation Operational Control System (OCX)

Monitor Station– Modernized command and control system - replaces legacy
system and adds modern features– Modern civil signal monitoring and improved PNT
performance– Robust cyber security infrastructure– New capabilities including civil signal performancemonitoring capability
Ground Antenna7Modernized GPS Civil Signals• Second civil signal “L2C”– Designed to meet commercial needs– Broadcast since 2005
– Currently 19 satellites broadcasting L2C• Third civil signal “L5”
– Meets transportation safety of life requirements– Uses Aeronautical Radio Navigation Service band
– Enables triple-frequency positioning techniques– Currently 12 satellites broadcasting L5• Fourth civil signal “L1C”– Designed for GNSS interoperability– Specification developed in cooperation with industry– Improved performance in challenged environments– Launches with GPS III in 2018

Continuous Broadcast of the new civil navigation “CNAV”
message on L2C and L5 began April 28, 20148

GPS SIS Performance Scoreboard

Wide Area Augmentation System(WAAS)• Satellite Based Augmentation System (SBAS)• Designed for aviation use, but available and used bymany GPS users today• Localizer Performance with Vertical Guidance (LPV)-200
approach is comparable to ILS Category I• Provides the capability for increased availability andaccuracy in position reporting, allowing more time foruniform and high quality air traffic management.
• Provides service for all classes of aircraft in all phasesof flight

10

WAAS/SBAS Aviation Benefits• Increased Runway Access• More direct en route flight paths• New precision approach services• Reduced and simplified equipment on board aircraft• Potential elimination of some ground-based navigation
aids (NDB, VOR, ILS) can provide a cost saving to air
navigation service provider

11

Wide Area Augmentation System(WAAS) Architecture

38 Reference
Stations

3 Geostationary
Satellite Links

3 Master
Stations

6 GroundEarth Stations

2 Operational
Control Centers

12

GEO Constellation
GEO 5/6 Satellite Acquisition–

Multiple IDIQ contracts awarded
September 2017
– Targeting early 2018 to award taskorder for delivery of GEO 7 to one
vendor–EUTELSAT 117 West B (ex SatMex 9) satellite–•–

GEO 7 Satellite acquisition

•

GEO 5
•

Provides full coverage of CONUS and Alaska

Integration activities started, expected operational
2018

GEO 6
Host satellite is SES-15, planned for 129 West• In-Orbit Testing completed December 2017
• Expected Operational in mid-2019•

LegendMilestone
Satellite Option Years

AMR

FY13

FY14

FY15

FY16

FY17

FY18

FY19

11/17
Lease End

FY20

FY21

Base

7/21
Base 7/20

GEO 6
GEO 7

FY23

7/20
Option

CRE
GEO 5

FY22

7/19

CRW

GEOs

•

Option 1

7/22
Option 2

4/18

6/19
2022

FY24

Current WAAS Performance
LPV

RNP 0.3

LPV - 200

More detailed information available at http://www.nstb.tc.faa.gov/reports/waaspan62.pdf

14

WAAS Dual Frequency Service• WAAS has implemented system changes to enable a L1/L5 user
– Upgraded reference station receivers to receive L5– Upgraded communication network to handle additional data (Dec 2017)– New safety computer with improved processor performance (Sep 2019)• Minimum Operational Performance Standards (MOPS) andStandards And Recommended Practices (SARPS) requirements
development is underway• Significant additional work needed to implement a dual frequency
WAAS Service– Preparing for FAA investment decision in 2019

• Have also installed non-operational test receivers at 6 WAAS
reference sites to record Galileo data
– Currently being collected for research purposes only15

Benefits of Dual Frequency Operations• Dual frequency L1/L5 service improves availability andcontinuity
L1

L1, L5

Simulation16

Procedures and Users Depending on
WAAS
Approach Procedures• 4527 WAAS Procedures
published (as of Jan 2018)– 3872 Localizer Performancewith Vertical guidance (LPV)
procedures– 655 Localizer Performance(LP) procedures

Users• Over 91,000 WAAS/SBAS equipped aircraft• All aircraft classes served in all phases of flight• WAAS/SBAS is enabling technology for FAA
NextGen– Automatic Dependent Surveillance Broadcast (ADS-B)– Performance Based Navigation (PBN)17

For Additional Information…

www.gps.gov

18

Thank You
Questions?

17