GPS and GNSS Research at Stanford University Sam

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

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 Ph. D Students: Lee Boyce, Ung-Suok Kim, Michael Koenig, Seebany Datta. Barua, Tsung-Yu Chiou, Dave De. Lorenzo, 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

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

Why Augmentation? QCurrent GPS and GLONASS Constellations Cannot Support Requirements For All Phases of Flight QIntegrity is Not Guaranteed QAll satellites are not monitored at all times QTime-to-alarm is from minutes to hours QNo indication of quality of service QAccuracy is Not Sufficient QEven with SA off, vertical accuracy > 10 m QAvailability and Continuity Must Meet Requirements

LAAS Components Courtesy: FAA

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

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

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

NSTB (FAATC/SU WAAS Prototype)

NSTB Accuracy Comparison (Center of Country)

NSTB Performance at Cold Bay, Alaska

NSTB Performance at Cold Bay, Alaska (2)

Integrity Beacon Landing System (IBLS)

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

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

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

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

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

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 at sea) that supports the warfighter when ceiling and visibility are limiting factors…” DEPARTURE ENROUTE OCEANIC / EN ROUTE INITIAL CLIMB TAKE OFF ARRIVAL TERMINAL NONPRECISION APPROACH CAT IIIA MISSED APPROACH 200 TAXI 100 0 Category (CAT) I - 200 FT DH and 1/2 Mile Vis CAT II - 100 FT DH and 1/4 Mile Vis CAT IIIA - 0 FT DH and 700 FT Vis

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

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

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