GPS (GNSS) Telecom Time Now and Future 2011 Telcordia-NIST-ATIS Workshop on Synchronization in Telecommunications Systems May 10-12, 2011

Transcription

1 GPS (GNSS) Telecom Time Now and Future 2011 Telcordia-NIST-ATIS Workshop on Synchronization in Telecommunications Systems May 10-12, 2011 Marc A. Weiss, Ph.D. Time and Frequency Division National Institute of Standards and Technology

2 GPS (GNSS) Update GNSS Systems GNSS Status and Future GNSS Failure Modes Conclusions & References 2

3 GNSS Systems: General Properties Position, Navigation, Timing (PNT) Four + synchronized timing signals from known locations in space required for navigation Two + frequencies measure ionosphere Control, Space, User Segments Open and Restricted Services 3

4 GNSS-aided Time and Frequency Systems T/F System Quartz Crystal Oscillator GNSS GNSS Rcvr Compare Tune Qz Osc. Output Freq. Or GPS Rcvr Rubidium Vapor Atomic Oscillator Compare Tune Rb Vapor Phy Pkg Qz Osc. Output Freq. Rb oscillator 100 to 1000 times better Holdover Performance T/F System Courtesy H. Fruehauf, ViaLogy LLC 4

5 GNSS for Telecom Timing Antenna required Top of building implies space rental, lightning issues Through window gives limited visibility, sats come and go, GEOs are fixed Receiver needs Qu or Rb oscillator Provides signal, steered to sats Stability/cost trade-offs Telecom timing signals required Error/failure/attack mitigation RAIM Duplicate/backup timing 5

6 GPS Satellite Signals entire navigation industry based on this code! 21.3 o L o L MHz C/A-Code Mcps, P-Code Mcps Data 50 bps Ionosphere 75 to 400 Km Free Electrons t Charged Particles t A/f 2 2 to 50 ns delay L 1 L 2 5 o Mask Angle L MHz P-Code Mcps Data 50 bps Four Satellites needed for 3-D navigation Maximum Doppler Shift between Satellites ~ ± 6KHz Courtesy H. Fruehauf, ViaLogy LLC 6

7 Time from GPS: Noise/Error Sources Problems at Receiver: Coordinates Multi-path interference Delays in cables Delay through receiver Receiver software Ephemeris error SV Clock Ionosphere Troposphere 7

8 Typical GPS Signal Time Error Budget Error Source Ionosphere (< 1000 km) Troposphere (< 20 km) GPS orbits GPS clocks Multipath ( clean environment) Receiver Noise Typical Error 3-15 ns (single frequency, using broadcast model) ns 6.0 ns (RMS) 6.0 ns (RMS) ns code ns carrier ns (RMS) code 3-6 ps (RMS) carrier 8

9 GPS Receiver Uncertainties for Time Simulator Active antenna delays vary with temperature Cable delays vary with temperature, Temp Co depends on equipment GPS Receiver: delays = +/- 500 ns 9

10 Receiver Delay Calibration Best systems can calibrate accurately to a few ns depending on antenna Use a good simulator Inject signal into antenna cable Calibrate cable separately use a cable with a low Temperature Coefficient Antenna calibration more difficult Most accurately done in an anechoic chamber Temperature coefficient strongly dependent on bandwidth and ability to reject out-of-band signals Receiver delay depends on processing technique Delay can be negative! Stability of delay over time depends strongly on hardware 10

11 GPS (GNSS) Update GNSS Systems GNSS Status and Future GNSS Failure Modes Conclusions & References 11

12 GNSS Status and Future GPS US (24+) Galileo EU (27) GLONASS Russia (24) Beidou/Compass China (35) 12

13 Present & Upcoming GPS, Glonass & Galileo Signals GAL-E5a GPS-L GAL-E5b GAL-E6a L2-Band (MHz) M M 1246 L2C GPS-L2 GLO-L GAL-E6b 1300 Future GLO-L3 L2 P(Y) P P Pilot SAR L1-Band (MHz) L1 C/A C/A 1559 L1C M GPS-L1 M 1602 C/A GLO-L WAAS, EGNOS, MSAS, GAGAN generated L1-C/A Look-alike Black and Blue Signals Operational ~5010 C-Band (MHz) ~5020 ~5030 GAL-C1 GAL-E2 L1 P(Y) GAL-E1 P Gone 13

14 GPS Presented by Lt. Col. Stephan Steiner, Chief Engineer, USAF GPS Wing, 21 Sep2010, CGSIC 14

15 GPS Presented by Lt. Col. Stephan Steiner, Chief Engineer, USAF GPS Wing, 21 Sep2010, CGSIC 15

16 GPS Presented by Lt. Col. Stephan Steiner, Chief Engineer, USAF GPS Wing, 21 Sep2010, CGSIC 16

17 GALILEO Galileo will be Europe s own global navigation satellite system It will be interoperable with GPS and GLONASS, the two other global satellite navigation systems. Galileo is a joint initiative of the European Commission (EC) and the European Space Agency (ESA). Consists of 30 medium Earth orbit satellites, associated ground infrastructure, and regional/local augmentations. Will offer a basic service for free (Open Service), but will charge user fees for premium services

18 The GALILEO Satellite Services Position, Velocity and Time Services: Open Service - providing positioning, navigation and timing services, free of charge, for mass market navigation applications (future GPS SPS) Commercial Service - provides added value over the Open Service providing commercial revenue, such as dissemination of encrypted navigation related data (1 KBPS), ranging and timing for professional use - with service guarantees Safety of Life Service - Comparable with Approach with Vertical Guidance (APV-II) as defined in the ICAO Standards and Recommended practices (SARPs), and includes Integrity Public Regulated Service - for applications devoted to European/National security, regulated or critical applications and activities of strategic importance - Robust signal, under Member States control Support to Search and Rescue Search and Rescue Service coordinated with COSPAS SARSAT 18 18

19 GLONASS Presented by Sergey Revnivykh, Deputy Director General, PNT Center, 21 Sep2010, CGSIC 19

20 GLONASS Presented by Sergey Revnivykh, Deputy Director General, PNT Center, 21 Sep2010, CGSIC 20

21 GLONASS K1 Launched Feb 26, 2011 Now under test Presented by Sergey Revnivykh, Deputy Director General, PNT Center, 21 Sep2010, CGSIC 21

22 Compass/ Beidou China may complete a 14-satellite regional system by in Geostationary orbits(geo) 5 in Inclined Geostationary orbits (IGSO) 4 in Middle-earth orbits (MEO) 1 MEO, 3 IGSO, and 4 GEO in orbit as of April 10, 2011 One GEO may not be usable China is currently developing COMPASS to reach Full Operational Capacity (FOC) around MEOs 3 GEOs (including 2 Beidou-1 satellites) 5 IGSOs

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25 GNSS Interoperability Issues Coordinate System GPS and Galileo plan on using the same system: ITRF Glonass uses a slightly different system Time Scale GPS and Galileo have agreed to transmit the GPS/Galileo Time Offset (GGTO) Goal: an objective of three nanoseconds (one meter) accuracy for the GGTO message has been accepted Glonass uses a different time scale, though known relationships are kept within bounds Signal Compatibility Generally all systems can be received by the same system 25

26 GPS (GNSS) Update GNSS Systems GNSS Status and Future GNSS Failure Modes Conclusions & References 26

27 Failure Modes GPS best feature and worst problem: it is extremely reliable Satellite failure modes can produce signals with large errors Receiver Autonomous Integrity Monitoring (RAIM) should compare all satellite signals and discard errors System design should compare GPS-based clock to local signals Receiver problems Satellites set unhealthy should not be used Firmware errors and wrong interpretations of specs Ionosphere/troposphere models Leap seconds Jamming: intentional and unintentional, Spoofing 27

28 GNSS Signals Are Vulnerable to Jamming and Spoofing Signals can be easily jammed Several incidents of accidental jamming Most telecom receivers can go into holdover for at least a week with few ill effects Wireless base-stations can be affected adversely Spoofing is becoming easier 28

29 Other GNSS Issues Ionosphere solar sunspot max 2013, though little activity lately Indoor positioning Signal Authentication 29

30 LightSquared L 2 Band: 1525 MHz 1559 MHz GPS L1 Band: MHz Center offsets: = 33MHz L 2 signal power: 1,500 W GPS signal power: W Testing being performed by experts from GPS, L 2, Government. Results due June 15 30

31 GPS (GNSS) Update GNSS Systems GNSS Status and Future GNSS Failure Modes Conclusions & Resources 31

32 Conclusions GNSS Now Global GPS civil service performance commitment met/exceeded continuously since Dec 93 Glonass operational, committed to replenish Galileo, Compass with experimental satellites GNSS Future GPS: new signals, more accuracy, yet backward compatible, more integrity information New/other systems: Glonass, Galileo, Compass Integration with indoor positioning GPS/GNSS failure modes: they exist and there are precautions Resources are available: see next slide 32

33 GNSS Resources U.S. Coast Guard Navigation Information Center Voice Announcement Resource Person Web Page Civil GPS Service Interface Committee (CGSIC) GNSS status and other info: da_final.htm U.S. Space-Based Positioning, Navigation, and Timing Policy: International GNSS Service (IGS) US Timing Labs NIST info: U.S. Naval Observatory: GPS World: Inside GNSS: Institute of Navigation 33

34 Extra Slides 34

35 GPS History from Brad Parkinson 35

36 GPS History from Brad Parkinson 36

37 U.S. Policy Presented by Col. Robert M. Hessin, Deputy Director, US National Coordination Office for Space-Based PNT, 21 Sep 2010, CGSIC 37

38 GPS Presented by Lt. Col. Stephan Steiner, Chief Engineer, USAF GPS Wing, 21 Sep2010, CGSIC 38

39 Galileo Constellation Configuration GALILEO DATA Walker 27/3/1 Constellation altitude ~23616 km SMA km inclination 56 degrees satellites in three Medium Earth Orbits (MEO) period 14 hours 4 min ground track repeat about 10 days 39 39

40 GALILEO News Contracts for deployment awarded Jan 7, 2010 Satellite production 14 satellites OHB System AG of Germany 1 st SV July 2012, 1 every 1.5 months, last March 2014 System support services, ThalesAleniaSpace, Italy Launch, Arianspace, France Ground-mission/control/ops infrastructure to be awarded mid

41 QZSS Presented by Shin ichi Hama,et. Al., ION GNSS

42 The Goal of GNSS Civil Interoperability Compatibility Do no harm Interoperability provides users a PNT solution using signals from different GNSS systems: No additional receiver cost or complexity No degradation in performance 42