GPS-aided Precision Time and Frequency Systems

Transcription

1 GPS-aided Precision Time and Frequency Systems as applied to Communications and Command/Control Terminals Approved for Public Release by the GPS Wing Aug Hugo Fruehauf August 2007, R3

2 Discussion Outline GPS Basics Basic GPS Applications GPS Signal Loss Mitigation The GPS Time and Frequency Engine Performance Characteristics Future GPS, Glonass & Galileo Signals 2

3 GPS Satellite Signals 21.3 o L o 20, Km (~12,531 mi.) 12-hr Orbit 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 MHz P-Code Mcps Data 50 bps L 1 L 2 Four Satellites needed for 3-D navigation 5 o Mask Angle Maximum Doppler Shift between Satellites ~ ± 6KHz 3

4 The GPS Carrier Modulation Signals Carriers (L1/L2) Phase Shift Keying (PSK) Modulation 1540 Cycles per C/A-Chip C/A - Code (L1) P- Code (L1/L2) Data (L1/L2) (AS) Encryption P becomes (Y) Transmitted in Phase Quadrature (90 Out of Phase) (SA) Degrad. Now set to Zero C/A Code P Code MCPS MCPS 50 BPS Y-Code Frequency Dither (On All Above Signals) 4

5 GPS Signal Structure Overview Carrier- Frequency C/A Code P-Code (+) Encryption Data MHz MHz 50 BPS Chipping Rate Chipping Rate L MHz Code Period 1023 Chips Code Repeats Every 1 ms ~1microsec Time Per Chip Different Gold Code I.D. s Each Sat Spatial Length per bit: 290 m, 960 ft. Code Period x Chips (~38 weeks) Code is Reset Every Week x Chips/Week ~0.1microsec Time Per Chip Same Code for Each Sat, But Different 7-day Section 37, 7-day Sections Available Spatial Length per bit: 29 m, 96 ft. NSA/JPO Crypto Keys For Authorized Users Only 1500 Bit Frame, 5 subframes (30S); Each Subframe 300 Bits (6S); 30 Bits Word, 24 Bearer Bits, 6 Bits Parity; Total 12.5 Minutes How Word For P-Code Acq. (Each Subframe) Clock and UTC Correction User Range Accur. (URA) Sat Health Sat Configuration Ionospheric Correction Model Ephemeris Coordinate Sys. (S/A) Degradation Selective Availability of C/A Signal Dither at Output of Sat Clocks Degradation Level of C/A Selectable by Grd. Comd. NOW set to Zero Almanac L MHz No-C/A P-Only Yes Yes Yes 5

6 GPS Signal Structure M L2 New L2C M New M-Code (Future) M MHz L MHz M MHz MHz MHz MHz MHz MHz MHz MHz C/A MHz P(Y) P(Y) MHz Spread Spectrum Signal, ~30 db below the receiver ambient noise level (Said to represent energy of a 25 watt light bulb at 11,000 miles distance) 6

7 GPS Signal Realities Antenna Pattern Horizon GPS Antenna: 12 Element L-Band Helical Phased Array (On-axis view) Received Power vs. SV Elevation Angle Zenith Received Power at 3dB Linearly Polarized Ant. (dbw) * dbw dbw dbw dbw L1-C/A L2C L1-P(Y) L2-P(Y) -166 ~1x10-16 watts* User Elevation Angle (deg) 7

8 Space Borne 1-Way 1 3D Ranging System The Realistic GPS System...The time is My position is... Satellite Time Codes Matching RCVR ie. SV1 to SV4 Time Codes t 1 t 2 t 3 T t τ τ τ τ 4 R 1 = C( t 1 + T - τ 1 ) R 2 = C( t 2 + T- τ 2 ) R 3 = C( t 3 + T - τ 3 ) R 4 = C( t 4 + T - τ 4 ) RCVR Clock Error Signal Travel Time SV Clock Error SV C/A Gold Code 4 Equations 4 Unknowns 8

9 Satellite Geometry and GDOP σp = DOP σ m Positioning Accuracy (X, Y, Z) Geometry (Dilution of Precision) Measurement Accuracy (UERE) Error Ellipsoid Elongated Poor GDOP Satellites bunched together Good GDOP (ideal case) One satellite overhead 3 on horizon, 120 apart in azimuth 9

10 GPS Satellite (Block II, IIA) Rockwell (RI) Major Characteristics Launch mass On-Orbit mass Solar Array Design Life Consumables Clocks 3,675 lb. 1,862 lb. 1,000 Watts 7.5 years 10 years (2) Rb, (2) Cs RI-Efr FTS All Have Been Launched 10

11 GPS Satellite (Block IIR) Lockheed-Martin Major Characteristics Launch mass 4,480 lb. On-Orbit mass 2,210 lb. Solar Array 1,100 Watts Design Life 7.5 years Consumables 10 years Clocks (3) Rb EG&G* *now Perkin-Elmer In Launching Phase 11

12 GPS Satellite (Block IIF) Boeing* * Was Rockwell International Major Characteristics Launch mass 4,634 lb. On-Orbit mass ~2,400 lb. Solar Array 1,560 Watts Design Life 15 years Consumables 15 years Clocks (2) Rb, (1) Cs EG&G* FTS** *Now Perkin-Elmer **Now Symmetricom In Launching Phase soon 12

13 Satellite Constellation All near perfect circular orbits 21 to 24 Satellites required for 24 x 7 coverage 30 GPS Satellites in Operation at present 13

14 The Other Operational GNSS GLONASS (Russia) ops since late 80s GLObal NAvigation Satellite System (GLObalnaya NAvigatsionnaya Sputnikovaya Sistema) 14

15 GLONASS GPS Comparison of GPS and GLONASS Parameter GLONASS GPS Ephemeris information presentation method 9 parameters of s/c motion in the geocentric rectangular rotated coordinate system Interpolation coefficients of satellite orbits Geodesic coordinate system SGS 85 WGS 84 Referencing of the ranging To the timer of GLONASS To the timer of GPS system signal phases system System time corrections relative to the Universal Coordinated Time (UTC) UTC (SU) UTC (USNO) Duration of the almanac 2.5 min 12.5 min transmission Number of satellites in the full spares spares operational system Number of orbital planes 3 6 Inclination Orbit altitude km km Orbital period 11 h 15 min 12 h Satellite signal division Frequency Division Code Division method Frequency band allocated (L1) ± 1MHz ± 0.5 MHz Type of ranging code PRN-sequence of maximal Gold Code length Number of code elements Timing frequency of code MHz MHz (C/A) Crosstalk level between two -48 db db neighboring channels Synchrocode repetition period 2 sec 6 sec Symbol number in the synchrocode

16 GPS and GLONASS active Satellite Constellation From GPS World From USNO website

17 Discussion Outline GPS Basics Basic GPS Applications GPS Signal Loss Mitigation The GPS Time and Frequency Engine Performance Characteristics Future GPS, Glonass & Galileo Signals 17

18 The Two Worlds of GPS World s s Civil and Military PVT World s s Civil and Military Timing/Sync Navigation and Positioning PVT (Position, Velocity, and Time) Precision Time and Frequency Generation and Synchronization Focus of Briefing! 18

19 Civil and Mil Applications Overview Oscillator Telcom Wireless Wireline E911 Grd. Mobile Comm. Airborne Comm. Time Transf. Sat. Terminals UTC, PRS s Aided GPS (Local Flywheel Devices) Networks, Internet Last Mile Utilities, Grids Survey Broadcast FAA-ATC P(Y) PVT Loran-C Sync Comm d Control C/A PVT IMU/Gyro Depot, Meas m Signal Anal. Radar Ranges Hi-Value Mobile Platforms Weapons Targeting Airborne Nav. Space Nav. Unaided GPS Grd. Portable Grd. Mobile Tracking Sport Scientific Meas mt Augmented GPS (Remote Aid Devices) JPALS DGPS WAAS EGNOS MSAS GAGAN SBAS LAAS 19

20 Civil and Military Signal Relationships GPS Sats L2 P(Y) + 50 bps L1 C/A, P(Y) + 50 bps L2 Mil P(Y) Code Mod. + Data Military SAASM ~6.2 x Chips; repeat each week 1023 Chips; repeat each ms Acquisition Aid Mil P(Y) Code Civil C/A Code Mod. + Data (<100ns Clock) Mod. + Data + <100ns Clock Crypto Key Real-time Ionospheric Corrections P(Y) PNT C/A PNT L1 Partial Ionos. Corrections (Model only) Typical GPS Receiver Europe s Galileo Other GNSS Systems Data + 1PPS 20

21 The New Mil GPS-SAASM SAASM Infrastructure The SAASM generation military GPS infrastructure meets the Tactical as well as the Strategic Warfare challenges of today: Tamper-Resistant SAASM Module on GPS receiver board to protects both HW and SW Unclassified fielding capability of GPS system when keyed Unclassified GPS Black Keys to reduce key-mgmt logistics Over-The-Air-Re-keying (OTAR) via GPS messages to automatically re-key authorized users Capability to allow authorized GPS user groups Direct P(Y)-Code Signal Acquisition to allow GPS receiver start-up without the Civil-C/A code signal Systems capabilities to greatly enhance the GPS SAASM functionalities 21

22 SAASM Hardware and Software Security Key Delivery GPS OTAR (after authentication) ELECTRONIC L1-C/A, L1- P(Y), L2- P(Y), + Data RECORD- KEEPING for HAE PHYSICAL SAASM RCVR PORTABLE USERS SAASM RCVR HOST EQUIPMENT(HAE) SAASM GPS P(Y)-CODE RECEIVER 22

23 The New Warfare Realities Civil Signal C/A-GPS Civil Signal C/A-GPS + Military Signal P(Y)-GPS Users World Civil Navigation and Timing >$10B Market and growing rapidly World Military Navigation and Timing USA and Allies Cold War Strategic Conflict Use of SA to degrade C/A Civil Accuracy (Worldwide effect) With C/A still available, no affect on military PPS Receivers Today s Tactical Conflicts C/A may not available, eliminating Civil use GPS (Local effect only) Need to operate without C/A, Need Physical Security Need Direct-P(Y) Signal Acq. 23

24 24 GPS Black Crypto Key GPS Satellites Civil C/A-Code Signal Mil P(Y)-Code Signal Antenna RF Analog Signal Proc Display, I/Os CSAC SAASM Based GPS PPS Receiver SAASM Security Module 1000s of Signal Correlators C/A and P(Y) Code Signal Bits Direct P(Y) Signal Acquisition Correlator Direct P(Y) Signal Acquisition Correlator Needs No Precision Time Sync Time Freq. A/Ph Micro Processors and Memory Crypto Signal Processing Digital Signal Processing

25 Direct-P(Y) Receiver Telecom Terminals Hand-Held, Portable Units GPS Crypto Key NO Host GPS Equipment Map Time/Frequency/Sync Telecom Terminals Precision Time Wristwatch still a Goal Manual input of Parameters via Keyboard 1PPS cable RS-232 cable Preferred Hot- Start Initialization for DP(Y) PLGR DAGR Typical Initialization Parameters for Direct P(Y) Acquisition Position Uncertainty Velocity Uncertainty Time uncertainty Almanac < 100 Km Radius < 100 Km/h +/- 2 Seconds (Goal) Can be days Old 25

26 Discussion Outline GPS Basics Basic GPS Applications GPS Signal Loss Mitigation The GPS Time and Frequency Engine Performance Characteristics Future GPS, Glonass & Galileo Signals 26

27 Jamming to Signal Ratio Signal Acquisition Threshold ~20 db Loss of Lock Regain Lock 1 w Jammer (C) For 1 kw Jammer (A) (B) RED modifications to referenced website chart by H Fruehauf 3-08 For 1 w Jammer: Regain Lock Loss of Lock Commercial GPS: (B) ~150 km from Jam r (A) ~50 km from Jam r Military GPS: Not 1 w & 75 db J/S (C) 27

28 NCW Non-Coherent CW CCW Coherent CW SCW Swept CW Commercial GPS Rcvr Jamming tests

29 Rockwell Collins SAASM Receiver >80-90 db J/S Performance*** ***A/J performance is based on 1 Jammer of any type. Full performance is classified. ml 29

30 GPS Signal Loss Mitigation; Backup Standards Cesiums (Primary Standards) Relatively high unit cost and maintenance Frequency Std., but not long-term TOD eloran/loran-c C Receivers Not Worldwide Coverage Next best to GPS, but needs TOD updates WAAS/EGNOS/MSAS/SNAS Inmarsats 10dB(+) Gain against J/S with 18 Dish Not a Total Solution for Jamming Inmarsat-3 s, etc. National (LF) Time Transmitters Usually limited geographic coverage Accuracies may not be sufficient SAASM-GPS P(Y)-code Receivers Best approach for authorized users Mitigates GPS C/A-code signal loss Requires COMSEC setup SAASM RCVRs replace GPS C/A receivers C/A-Code P-Code GPS s 30

31 GPS Signal Loss Mitigation, Qz or Rb Holdover Oscillator System GPS Satellite Atomic Oscillators GPS-aided Qz or Rb Time/Frequency Sync System GPS L1-C/A Com l RCVR Or Mil P(Y)-code Signal GPS- SAASM L1/L2-P(Y) Mil RCVR 1 PPS Sync TOD Rubidium Holdover Oscillator Quartz Holdover Or.. Oscillator Signal Processing Circuits Outputs/ Inputs Displays Frequency Time Network GPS Crypto Keys Continuous Disciplining Learning Algorithms RS-232 Ext. Sync PC TOD and Ext. Sync Option 31

32 GPS-aided Disciplining T/F System Quartz Crystal Oscillator GPS GPS 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 500 times better Holdover Performance T/F System 32

33 Rubidium Holdover Oscillator System Periodic Disciplining No GPS-aiding Rubidium Time/Frequency Sync System Rubidium Holdover Oscillator Outputs/Inputs Displays Frequency Time Satellite Atomic Oscillators Alarm/Fault - Rb Lock + Other Ref. Lock - TFOM 3 (better than 100ns, and better than 1E-11 Frequency GPS Mil P(Y)-code Signal Discipline Circuits Learning Algorithms Network RS-232 Ext. Sync 1 PPS Sync DAGR Frequency Accuracy of ~1E-10, takes ~3 minutes disciplining time ~2E-11, takes ~15 minutes ~1E-11, takes ~30 minutes TOD PLGR Periodic Disciplining with handheld 33

34 Discussion Outline GPS Basics Basic GPS Applications GPS Signal Loss Mitigation The GPS Time/Frequency Engine Performance Characteristics Future GPS, Glonass & Galileo Signals 34

35 Typical Communications Applications T/F Sync System 35

36 Redundant Modular Time & Freq. System (3U) CommSync II GTF Module Plug-In Output Modules Commercial C/A-Code GPS RCVRs OR Imbedded SAASM Receiver Atomic Oscillators OR Qz Oscillators 36

37 Single String Modular Time & Freq. System (2U) Plug-in Output Modules Commercial C/A-Code GPS RCVRs Atomic Oscillators OR Qz Oscillators Ethernet & I/O Ports OR Imbedded SAASM Receiver 37

38 Single String Modular Time & Freq. System (1U) Atomic Oscillators OR Qz Oscillators Plug-in Output Modules Commercial C/A-Code GPS RCVRs OR Imbedded SAASM Receiver Ethernet & I/O Ports 38

39 GPS Time & Frequency Engines Can also come with Imbedded SAASM Receiver Sub-Systems and Modules for Special Purpose Applications 39

40 Discussion Outline GPS Basics Basic GPS Applications GPS Signal Loss Mitigation The GPS Time and Frequency Engine Performance Characteristics Future GPS, Glonass & Galileo Signals 40

41 5 UTC 0-5 Typical Time USNO Error SAASM to Calibration UTC locked to GPS All 4 Days (T/F System, 4-Day 4 Test) USNO SAASM Calibration Data Time Error (ns) Total Mean Std Dev RMS Nanoseconds Time Day 1 Day 2 Day 3 Day Seconds X10 41

42 Typical Time Error to UTC locked to GPS Time; < 20ns rms, 50ns Peak to UTC ns ns 42

43 Typical Holdover Time Error to UTC unlocked (T/F System) Microseconds ~7 to 10 us 1 Day Qz Oscillator (with modeling) Time ~4 to 6 us 7 Days Rb Oscillator (no modeling) 43

44 Typical Frequency Error to UTC locked to GPS 1.0x10-11 (T/F System) Tau = 300 Sec Number of Points = 1008 Long Term: ZYFER RCVR Vs. Ch 1 Frequency Data FreqOffset Quad Fit: x = a + bt + ct^2 Drift Quad Fit: x = a + bt + ct^ :48:31 Fractional Frequency x x10-12 Frequency x Frequency Offset = E-14 Drift = E-14 per day Phase Offset = E+1 Sec MJD 3.5 days 44

45 Typical Holdover Freq. Error to UTC unlocked (T/F System) ~1 to 2E-10 1 Day Qz Oscillator (with modeling) Frequency ~2 to 5E-11 7 Days Rb Oscillator (mo modeling) 45

46 Frequency Stability GPS disciplined Oscillator GPS RCV R Short-Term performance mainly due to 3 ns+ multi-path type noise and RCVR to Osc servo loop noise Com l and Mil Signal Performance from GPS RCV R vs. UTC Hump mainly due to RCV R to Osc servo loop time constant, temp, multi-path noise, and ionosphere s a 5 MHz Low Noise Module Performance locked to GPS Worst - Best GPS Satellite Clock performance Ground & in Space, NOT MEASURABLE from Space ~1.4E-13 Worst - Be st GPS Satellite Clock performance Ground & in Space MEASURABLE ~1.4E

47 Typical Freq. & Time Accuracy vs. Warm-up Time Ref zero Rb Lock at ~3 min; Freq. Acc. ~1E-9 Time Rb Resonance Search Mode, ~ ±1E-9 Frequency GPS discipline at ~13 min; Freq. Acc. ~1E-11 Ref zero GPS Lock at ~4.5 min; Freq. Acc. ~2E-10 47

48 Discussion Outline GPS Basics Basic GPS Applications GPS Signal Loss Mitigation The GPS Time/Frequency Engine Performance Characteristics Future GPS, Glonass & Galileo Signals 48

49 GPS & Glonass Signals Today L2-Band (MHz) GPS-L2 GLO-L2 L2 P(Y) P P L1-Band (MHz) L1 C/A C/A WAAS, EGNOS, MSAS, GAGAN generated L1-C/A Look-alike 1563 GPS-L C/A GLO-L1 Black and Blue Signals Operational L1 P(Y) P

50 GPS L2C Civil & M-Code M Military Signal Additions GPS Block IIR-M Satellites L2-Band (MHz) M L2C M GPS-L2 GLO-L2 L2 P(Y) P P L1-Band (MHz) L1 C/A C/A WAAS, EGNOS, MSAS, GAGAN generated L1-C/A Look-alike 1563 M GPS-L M C/A GLO-L1 Black and Blue Signals Operational L1 P(Y) P

51 GPS L5 Civil Signal Addition L2-Band (MHz) M L2C M 1246 GPS Block IIF Satellites GPS-L5 GPS-L2 GLO-L2 L2 P(Y) P P L1-Band (MHz) L1 C/A C/A WAAS, EGNOS, MSAS, GAGAN generated L1-C/A Look-alike 1563 M GPS-L M C/A GLO-L1 Black and Blue Signals Operational L1 P(Y) P

52 GPS L1C Civil Signal Addition L2-Band (MHz) M L2C M 1246 GPS Block III Satellites GPS-L5 GPS-L2 GLO-L2 L2 P(Y) P P L1-Band (MHz) L1 C/A L1C M GPS-L1 L1 P(Y) 1587 M C/A 1602 C/A GLO-L1 P WAAS, EGNOS, MSAS, GAGAN generated L1-C/A Look-alike Black and Blue Signals Operational

53 Glonass L3 Signal Addition GPS-L L2-Band (MHz) M L2C M GPS-L2 GLO-L2 Future GLO-L3 L2 P(Y) P P L1-Band (MHz) L1 C/A L1C M GPS-L1 L1 P(Y) 1587 M C/A 1602 C/A GLO-L1 P WAAS, EGNOS, MSAS, GAGAN generated L1-C/A Look-alike Black and Blue Signals Operational

54 Galileo Signals GAL-E5a GPS-L5 L2-Band (MHz) M L2C M GPS-L2 GLO-L2 Future GLO-L3 L2 P(Y) P P L1-Band (MHz) L1 C/A L1C M GPS-L1 L1 P(Y) M 1587 C/A 1602 C/A GLO-L1 P WAAS, EGNOS, MSAS, GAGAN generated L1-C/A Look-alike Black and Blue Signals Operational

55 Galileo Signals GAL-E5a GPS-L GAL-E5b L2-Band (MHz) M L2C M GPS-L2 GLO-L2 Future GLO-L3 L2 P(Y) P P L1-Band (MHz) L1 C/A L1C M GPS-L1 L1 P(Y) M 1587 C/A 1602 C/A GLO-L1 P WAAS, EGNOS, MSAS, GAGAN generated L1-C/A Look-alike Black and Blue Signals Operational

56 Galileo Signals GAL-E5a GPS-L5 GAL-E5b L2-Band (MHz) GAL-E6a M M 1246 L2C GPS-L2 GLO-L GAL-E6b 1300 Future GLO-L3 L2 P(Y) P P Pilot L1-Band (MHz) L1 C/A L1C M GPS-L1 L1 P(Y) M 1587 C/A 1602 C/A GLO-L1 P WAAS, EGNOS, MSAS, GAGAN generated L1-C/A Look-alike Black and Blue Signals Operational

57 Present & Upcoming GPS, Glonass & Galileo Signals GAL-E5a GPS-L5 GAL-E5b L2-Band (MHz) GAL-E6a 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-L1 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 57