Global Navigation Satellite System (GNSS) GPS Serves Over 400 Million Users Today. GPS is used throughout our society

Transcription

1 Global avigation Satellite System (GSS) For freshmen at CKU AA December 10th, 2009 by Shau-Shiun Jan ICA & IAA, CKU Global avigation Satellite System (GSS) GSS (Global Positioning System, GPS) Basics Today s Accuracy Tomorrow s Accuracy (2009 & even more in 2012) Beyond Accuracy Real time error bounds (SBAS & GBAS) Indoors & downtown (television signals) Applications Last Thoughts Many slides of this presentation are from Prof. Per Enge, Stanford University. Thanks! 1 2 GPS is used throughout our society Personal & car navigation Aircraft navigation & surveillance Farming Courtesy: Dr. Sherman Lo Asset Tracking (kids, pets,etc.) Fleet Management Electronic Tolling Cellular & other network timing Supply Chain & Inventory Control Maritime navigation & surveillance And many more! 3 GPS Serves Over 400 Million Users Today 1973: DoD approval 1975: first satellite 1995: 24 production satellites 2009: 31 satellites military, aviation maritime, space, auto-farming, precision construction, telecommunications, E-911, car navigation, animal tracking, etc. 4

2 GPS Signal Components: avigation Data, PR Code & RF Carrier 6000 km 300 m How it works from Misra and Enge, cm 6 Auto-Correlation Properties Present GPS Signal Spectrum L2 : MHz L1 : MHz Time shift between replica code and received code Received power density: W/m 2 Received power: W into a reasonably sized hemispherical antenna Spread spectrum for: ranging g discriminate reflections multiple access without time or frequency multiplexing modest rejection of radio frequency interference 7 8

3 Scatter Plots for Today s GPS Present and Future Spectra of GPS Signals Stand Alone GPS DGPS at 10 km Today s satellites E E 1 m 10 m 1 m 10 m L2 : MHz L1 : MHz ew satellites launched beginning in 2005 DGPS at 100 km 1m 10 m E 1m 10 m E DGPS at 1000 km ew satellites launched beginning g in 2009 L2 : MHz L1 : MHz 8 IIR-M on orbits today 9 L5 : MHz L2 : MHz L1 : MHz 10 Faster Codes Give Better Performance in oise and Multipath Ionospheric Measurement and Beat Frequencies Correlation peak for C/A code (1 Mcps) MHz 75 cm ML MHz WL 86 cm -300 m 300 m -30 m 30 m Correlation peak for L5 code (10 Mcps) L5 : MHz L2 : MHz L1 : MHz MHz 5.87 m EWL 11 12

4 Tomorrow s Accuracy Beyond Accuracy Part I: Integrity 1m 10 m E 1m 10 m E Stand-Alone DGPS to 1000 km? Accuracy measured at the 95% level after the fact Pilots need a guaranteed bound on error size Pr(true error exceeds bound)<10-7 Independent monitor networks deliver error bounds in real time On airport monitoring provides 2 s TTA (time to alarm) Continental monitoring provides 6 s TTA Military recently recognizes need for error bounding Link Sitka, Alaska: Runway 11 Centerline Kodiak, Alaska: Runway 25 Centerline 15 16

5 On-Airport Monitoring (GBAS) GPS constellation VHF data broadcast of airport corrections data for error bounding Continental Monitoring etworks (SBAS) GPS constellation Geostationary broadcast of 1.) Continental corrections 2.) Data for error bounds 3.) Ranging gsignal Multiple GPS receivers used for cross-checking & redundancy Airport Property Courtesy: Per Enge Central processor to generate corrections & error bounding data Link 17 WAAS: Operational on July 10, 2003! MSAS: Operational on Sept. 27, 2007! Link Reference receivers Courtesy: Per Enge Uplink station Central processor 18 SBAS Today Challenge: Ionosphere WAAS CWAS EGOS GAGA MSAS SAS 19 20

6 Performance of SBAS Beyond Accuracy Part II: Continuity Indoors & downtown assisted GPS (supplant GPS nav. message) ranging from cell towers or television signals Hackers motivate civilian anti-jam basic backup network (BB) of traditional nav. aids inertial aiding to extend averaging time Courtesy: Per Enge ring nulling & beam steering antennas Stand alone DGPS SBAS ew signals help, but we need more Television Signals Are Designed to Go Indoors and Downtown (from Rosum Inc.) Applications 23 24

7 Joint Precision Approach Landing System (JPALS) Satellite avigation Vision - Aviation Courtesy: Stanford GPS Lab 25 Courtesy: Stanford GPS Lab 26 Air Traffic Control Automation Last Thoughts Galileo (delayed ) Compass-2 (one MEO on orbit since April 2007) Quasi-Zenith Satellite System (similar idea in Taiwan) GLOASS (FDMA to CDMA soon) Courtesy: Dr. R. Teo 27 28

8 GPS Modernization and Galileo In L1 (1575MHz) and L5 (1176MHz) band, the center frequency of GPS and Galileo is identical. Compass Frequency Plan Compared with GPS and Galileo On April 13, 2007, China launched the first MEO satellite in its Compass GSS system, 21,550 km above the Earth. (GPS: 20,184 km; Galileo: 23,222 km) It has been transmitting on L1, E6 and E5b. Chip Rate Code Length BOC Center Modulation Frequency GPS 1.023MHz 1 milliseconds L1, L2, L5 Galileo 1.023MHz 4 milliseconds E1, E5, E6 29 Courtesy: Stanford GPS Lab 30 GSS Facts Currently, 30 GPS satellites on orbit (31 sometimes) Currently, 19 GLOASS satellite on orbit May 2000, Selective Availability (SA) off July 2003, U.S. Wide Area Augmentation System (WAAS) operational February 2005, 1st Japanese MTSAT launched September 2005, 1st new L1/L5 WAAS GEO Launched September 2005, 1st Modernized GPS satellite launched (Civil Codes on L1 and L2) October 2005, 2nd L1/L5 WAAS GEO launched December 2005, 1st GALILEO test satellite launched April 2007, 1st Chinese Beidou satellite launched September 2007, Japanese MSAS operational March 2009, 1 st Modernized L1/L2/L5 GPS Satellite Launched (Civil Codes on L1, L2 and L5) 31 What you need to do before working on GSS? Math: Linear Algebra (matrix), Engineering math (Fourier and Laplace), Probabilities (Statistic) Statics, Dynamics, Fluid, Structure, Thermodynamics, Signal and Control. Importantly, open your mind! 32