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GPS and GNSS Research at Stanford University
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  1. GPS and GNSS Research at Stanford University Sam Pullen, Per Enge, Todd Walter, Sherman Lo, Jason Rife, and Brad Parkinson Stanford University http://scpnt.stanford.edu

  2. GPS People at Stanford • Aero/Astro Faculty: Per Enge, Brad Parkinson, Bob Twiggs, Dave Powell • Senior Research Engineers: Todd Walter, Sam Pullen • Research Associates: Eric Phelts, Sherman Lo, Jason Rife • Research Engineers: Ming Luo, Juan Blanch, Godwin Zhang, Doug Archdeacon • Postgraduate Researcher: Jiyun Lee • Consultant: A.J. Van Dierendonck • PhD Students: Lee Boyce, Ung-Suok Kim, Michael Koenig, Seebany Datta- • Barua, Tsung-Yu Chiou, Dave DeLorenzo, Ju-Yong Do, Hiroyuki • Konno, Alexandru Ene, Di Qiu, Alex Chen, Grace Gao, Eui-Ho • Kim, Nikolai Alexeev, Mohamad Charafeddine • Support: Tom Langenstein (SCPNT), Sherann Ellsworth, Dana Parga • Allied Efforts (not including those within SCPNT): • ARL: Profs. Steve Rock and Bob Cannon • Hybrid Systems Lab: Prof. Claire Tomlin • Mechanical Engineering: Prof. Chris Gerdes • Geophysics: Prof. Paul Segal • University of Colorado: Prof. Dennis Akos • Illinois Institute of Technology: Prof. Boris Pervan • University of Minnesota: Prof. Demoz Gebre-Egziabher • MIT: Prof. Jonathan How

  3. GPS Overview • 24+ Satellites • 12 Hour Orbits • 6 Orbital Planes • 1 Way Ranging • Atomic Clocks • Spread Spectrum • Global 3D Positioning • <100 m Horiz. • Requires at Least 4 Satellites in View • Declared Fully Operational in July 1995 • Operated by U.S. Air Force in Colorado Springs, CO

  4. Why Augmentation? • Current GPS and GLONASS Constellations Cannot Support Requirements For All Phases of Flight • Integrity is Not Guaranteed • All satellites are not monitored at all times • Time-to-alarm is from minutes to hours • No indication of quality of service • Accuracy is Not Sufficient • Even with SA off, vertical accuracy > 10 m • Availability and Continuity Must Meet Requirements

  5. LAAS Components Courtesy: FAA

  6. WAAS Components Courtesy: FAA • Network of Reference Stations • Master Stations • Geostationary Satellites • GEO Uplink Stations

  7. WAAS and LAAS extend GPS Navigation Capabilities WAAS Today NPA WAAS Future L-NAV V-NAV 350 ft DH LAAS Near-Future Benefit: Lower DH GLS 250 ft DH CAT I 200 ft DH LAAS End-State CAT II 100 ft DH CAT III 0-50 ft DH Courtesy: Sherman Lo Requirement: Better Accuracy, Tighter Bounds DH = Decision Height

  8. GPS Research Timeline at Stanford Development and validation of WAAS integrity equation Beginning of JPALS and LORAN research FAA LAAS Integrity Panel (LIP) formed Development of LAAS carrier-smoothed code architecture Completion of example LAAS ground system design FAA WAAS Integrity and Performance Panel (WIPP) formed RAIM, IBLS, WAAS concept development 1990 1995 2000 2004 WAAS NSTB prototype development and testing Flight testing of early IBLS and WAAS prototypes GPS/UWB RFI Testing FAA WAAS Certification (July 2003) WAAS flight-test validation (Lake Tahoe) LAAS IMT prototype development and testing FAA Awards CAT I LAAS Ground System Contract 737 IBLS-guided autolands in Central CA Alaska and Moffett Field Flight Tests

  9. NSTB (FAATC/SU WAAS Prototype)

  10. NSTB Accuracy Comparison (Center of Country)

  11. NSTB Performance at Cold Bay, Alaska

  12. NSTB Performance at Cold Bay, Alaska (2)

  13. Integrity Beacon Landing System (IBLS)

  14. - United/Boeing 737 Autoland Results 110 Automatic Landings of Boeing 737-300 (Crows Landing, CA)

  15. LAAS Architecture Overview airport boundary Corrected carrier-smoothed -code processing -VPL, LPL calculation Cat I/II/III Cat I GPS Antennas VHF Antennas Airport Pseudolites (optional) LGF Ref/Mon Rcvrs. and Processing VHF Data Broadcast

  16. IMT GPS SIS 7 P Database 2 A A SISRAD 1 3 6 C D MQM Smooth B SQR B LAAS SIS 4 24 8 SQM prototype 5 10 F E SQM DQM 26 14 11 L 9 VDB Message Formatter & Scheduler 13 12 M VDB TX 25 23 G Executive Monitor (EXM) 15 7 LAAS SIS H Correction 19 18 27 22 VDB Monitor O 29 31 16 N 20 VDB RX 28 30 17 I K J Average MRCC sm-Monitor 21 Q LAAS Ground System Maintenance IMT Functional Flow Diagram

  17. “Evil Waveform” Failure Mode Example Correlation Peaks   Normalized Amplitude 1/fd Code Offset (chips) Comparison of Ideal and “Evil Waveform” Signals for Threat Model C C/A PRN Codes Volts Chips Note: Threat Model A: Digital Failure Mode (Lead/Lad Only: ) Threat Model B: Analog Failure Mode (“Ringing” Only: fd)

  18. Multicorrelator EWF Monitor CPROMPT CLATE CEARLY “Ratio Tests” (CLATE / CPROMPT) Normalized Amplitude “-Tests” (CEARLY-CLATE) Code Offset (chips)

  19. DEPARTURE ENROUTE ARRIVAL NON-PRECISION APPROACH CAT I CAT II CAT IIIA OCEANIC / EN ROUTE TERMINAL INITIAL CLIMB TAKEOFF JPALS MISSED APPROACH 200 TAXI 100 0 Category (CAT) I - 200 FT DH and 1/2 Mile VisCAT II - 100 FT DH and 1/4 Mile VisCAT IIIA - 0 FT DH and 700 FT Vis JPALS Mission Need Statement JROC validated Mission Need Statement, August ‘95 “…a rapidly deployable, adverse weather, adverse terrain, survivable, maintainable, and interoperable precision approach and landing system (on land and at sea) that supports the warfighter when ceiling and visibility are limiting factors…”

  20. Aircraft Carrier Landing Targeted Hook Touch Down Point Between 2 & 3 Wires 1 Wire 2 Wire 3 Wire Hook engages 3 wire 4 Wire

  21. SRGPS “At Sea” Challenge Yardarm Antennas Yardarm (Starboard) Antenna Yardarm (Port) Antenna

  22. Technical Challenges and Opportunities • Ionosphere Spatial Decorrelation • Rare ionosphere storms can create regions of unusual spatial decorrelation • Mitigated by WAAS and LAAS monitoring, but observability cannot be guaranteed • JPALS mitigates with dual-frequency removal of ionosphere measurement effects • Rare-Event Error Bounding • “Tails” of GNSS error distributions are fatter than predicted by Gaussian • Insufficient data exists to ID tail distributions • Exploiting GPS and GNSS Modernization • Signal and integrity enhancements in GPS III • Galileo ranging satellite constellation • 2nd civil frequency (GPS L5 / Galileo E5)