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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

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 NASA and FAA-Funded GPS Ph.D. Graduates
Penny Axelrad: Faculty of University of Colorado Changdon Kee: Faculty of Seoul National University Boris Pervan: Faculty of Illinois Inst. of Technology Glenn Lightsey: Faculty of UT Austin Demoz Gebre-Egziabher: Faculty of Univ. of Minn. Gabe Elkaim: Faculty of UC Santa Cruz Shau-Shiun Jan: Faculty in Taiwan The following founded IntegriNautics, a company specializing in high integrity positioning: Clark Cohen: President and founder Stewart Cobb: co-founder Dave Lawrence: co-founder Paul Montgomery: Integrinautics Mike O'Connor: Integrinautics Tom Bell: Integrinautics (now at LM) The following founded Traxsis, a company specializing in internet based positioning: Roger Hayward: President and founder Jock Christie: Traxsis co-founder Rich Fuller: Traxsis The following founded Nav3D, a company specializing in 3-D perspective displays: Andy Barrows : President and founder Keith Alter: Nav3D co-founder Awele Ndili: Cofounder of M Shift Sam Pullen: Senior Research Engineer leading the LAAS effort at Stanford. Matt Rabinowitz: Co-Founder of Rossum Ping-Ya Ko: Engineer in Taiwan Y.C. Chao: Co-Founder of Televigation Yeou-Jyh Tsai: Engineer at ITRI in Taiwan Ran Gazit: Engineer at Rafael in Israel Jaewoo Jung: Trimble Navigation Andy Rekow: Engineer at John Deere Eric Phelts: Research Associate WAAS & LAAS Harris Teague: Seagull Technology Inc. Eric Abbott: Engineer with L3 Communications Hiro Uematsu: Engineer with NASDA Donghai Dai: Engineer with Televigation Sharon Houck: Engineer at Seagull Technology Andrew Hansen: Engineer at Meta-VR Konstantin Gromov: Engineer at JPL Eric Olsen: Engineer at Johns Hopkins APL Gang Xie: Engineer at Motorola Sherman Lo: Research Associate (LORAN) Jenny Gautier: Research Associate (JPALS)

4 Projects at Stanford FAA DoD DoT Office of Technology and Licensing
Wide Area Augmentation System Local Area Augmentation System LORAN Datalink and GPS Backup DoD JPALS (land and sea-based versions) DoT UWB Analysis and Testing of Interference to GPS Office of Technology and Licensing Atlantis John Deere Autonomous Tractor

5 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

6 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

7 Aircraft Guidance Goals
Key Elements: Accuracy Availability Integrity Continuity The key elements in navigation aids for aviation are: accuracy, availability and integrity. Accuracy is the difference between what is reported to the pilot and the true position of the aircraft. Along with the position of the aircraft the WAAS user equipment will supply the confidence in that position which is reported in terms of possible extent of the position error. Availability is when the position in combination with the position confidence does not interfere with potential path obstructions. Integrity is achieved by continuously providing a position and confidence pair so that the position never exceeds the confidence level without a warning. Courtesy: Rich Fuller Integrity: Accuracy < Protection Limit

8 LAAS Components Courtesy: FAA

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


11 WAAS and LAAS extend GPS Navigation Capabilities
WAAS Today NPA WAAS Future L-NAV V-NAV 350 ft DH Lower DH Benefit: LAAS Near-Future GLS 250 ft DH CAT I 200 ft DH LAAS End-State CAT II 100 ft DH CAT III 0-50 ft DH WAAS extends navigation capabilities of GPS. Allows NPA but more importantly approaches with vertical guidance These are generally lower pilot work load/less configuration changes Lower landing minimums allows for operations in more adverse visibility conditions Courtesy: Sherman Lo Requirement: Better Accuracy, Tighter Bounds DH = Decision Height

12 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

13 NSTB (FAATC/SU WAAS Prototype)

14 NSTB Accuracy Comparison (Center of Country)

15 NSTB Performance at Cold Bay, Alaska
These histograms are another way of representing the data. Here instead of a two-dimensional histogram we have three separate one-dimensional distributions. They show, from top to bottom, the accuracy, integrity, and availability of the system. As with the triangle chart the probabilities are plotted on a logarithmic scale. The logarithmic scales are used to emphasize the tails of each distribution. We already have great confidence in the TMS operation the vast majority of the time. We are now interested in exceptions. The middle histogram is of primary interest. It shows the ratio of actual error to the one sigma value(sV). For reference, a gaussian curve is also shown. This parabola would be applicable if all the errors were gaussian, zero mean, and independent. As can be seen, the errors are more tightly distributed than the gaussian reference. All but seven of the 259,602 data points have values less than These seven points can also be seen in the Triangle chart with a corresponding VPL of roughly 8.5 meters.

16 NSTB Performance at Cold Bay, Alaska (2)
The triangle chart of actual performance at Cold Bay shows 90% availability for Cat I 96% availability for IPV and many points “clipped” at the top when the VPL exceeded 25 meters. Overall the performance is not too bad but has substantial room for improvement. Remember this is our worst performing station. Most were significantly better. Errors caused by PRN 18 can be seen in the CAT I region.

17 Queen Air Flight Test Aircraft

18 Tunnel Display Bank angle Final approach pathway Flight path vector
Vertical deviation Horizon line Ground- speed Heading Courtesy: Keith Alter Distance to touchdown Horizontal deviation

19 Localizer Approaches at Moffett Field
Ask: “so what if pilot is 1 dot off? Keep in mind that the separation between runways at SFO is 700 feet.” Roll activities not significantly different Jock: mention ILS can go unstable Courtesy: Sharon Houck

20 Integrity Beacon Landing System (IBLS)

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

22 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

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

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

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

26 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…” INITIAL CLIMB OCEANIC / EN ROUTE TERMINAL NON-PRECISION APPROACH ARRIVAL DEPARTURE TAKE OFF TAXI CAT I CAT II CAT IIIA 200 100 MISSED APPROACH Category (CAT) I FT DH and 1/2 Mile Vis CAT II FT DH and 1/4 Mile Vis CAT IIIA - 0 FT DH and 700 FT Vis ENROUTE JPALS

27 JPALS Operational Environments
Shipboard Tactical Fixed Base Special Missions

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

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

30 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)

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