Present and Future Global Navigation Satellite Systems (GNSS)

More documents

Recommendations

Info

Anti-Spoofing (A-S) • On block II satellites P-code is replaced by a secret Y-code (actually the P-code is encrypted) • To prevent military receivers from tracking "false" GPS satellites and to prevent jamming • Only (military) receivers with the appropriate "key" can use the Y-code • Two frequency GPS receivers cope with A-S in the following way Signal squaring on L2: L1 code & phase, L2 half wavelength phase Cross-correlation: L1 code & phase, Y2-Y1 code & L2-L1 phase P/W tracking: L1 code & phase, L2 code & phase Anti-Spoofing will always result in some loss of information, even if they can cope with A-S, the signal-to-noise ratio is worse than w/o A-S! • A-S was enabled on Monday 31 January 1994 0h00m, occasionally off for testing and other purposes 18 GEO2TECDI – Bangkok, May, 2009 – GNSS Lecture 2
Selective Availability (SA) – 1990-2000 • Intentional degradation of satellite signals by "Dithering" of satellite clock (through adding periodic errors to the satellite clock with periods of 5-7 minutes) Introducing deliberately errors in the broadcast ephemerides Classified algorithm and characteristics • To provide 100 m horizontal and 170 m vertical accuracy (95% confidence level) for C/A-code navigation • Ways to mitigate the negative effects for positioning Military receivers are able to overcome SA Use Glonass instead ☺ Can be overcome by differential GPS operation (much better than absolute positioning) • Implemented on all block II satellites, but not block I, although it is was off on some block II satellites • Was operational from March 1990 until May 2nd 2000 (none during the 1st Gulf war), switched off on May 2nd at 4:05 UTC!! 19 GEO2TECDI – Bangkok, May, 2009 – GNSS Lecture 2
Page 1 and 2: Present and Future Global Navigatio
Page 3 and 4: Principle of Satellite navigation S
Page 5 and 6: Global Navigation Satellite Systems
Page 7 and 8: NAVSTAR GPS Block II Satellite sola
Page 9 and 10: GPS Satellite Ground Tracks 90 60 3
Page 11 and 12: 80 60 40 20 0 270 −20 −40 −60
Page 13 and 14: GPS Signal Components • All signa
Page 15 and 16: Examples of GPS Receivers PC card m
Page 17: RINEX: Receiver INdependent EXchang
Page 21 and 22: GPS Services SPS/SA: SPS PPS Standa
Page 23 and 24: GPS PRN 23 Anomaly, 1 Jan, 2004 500
Page 25 and 26: Modernized Signal Evolution Present
Page 27 and 28: GEO2TECDI - Bangkok, May, 2009 - GN
Page 29 and 30: Introduction to Glonass GLONASS Rus
Page 31 and 32: GEO2TECDI - Bangkok, May, 2009 - GN
Page 33 and 34: GLONASS signal structure (2) Differ
Page 35 and 36: The 4 GALILEO arguments - European
Page 37 and 38: Galileo added value • Under contr
Page 39 and 40: GALILEO In Flight Configuration Nav
Page 41 and 42: GPS versus Galileo GPS Satellites:
Page 43 and 44: COMPASS 43 GEO2TECDI - Bangkok, May
Page 45: QZSS 45 GEO2TECDI - Bangkok, May, 2

Present and Future Global Navigation Satellite Systems (GNSS)

Create successful ePaper yourself

Delete template?

Save as template?