Septentrio en GLONASS receiver design

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Frank Boon geeft een update van de mogelijkheden die Septentrio heeft met GLONASS

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Septentrio en GLONASS receiver design

  1. 1. Impact of GLONASS on receiver design FDMA versus CDMA Frank Boon NiN Workshop 27/03/09
  2. 2. Background  Prototyped GPS+GLONASS PolaRx2  based on 4 Proprietary RF Chips  not commercialized : poor GLONASS constellation  served as engineering lessons platform  GLONASS ‘resurrection’ increased demand  AsteRx2 designed as GPS+GLO+GAL from start  AsteRx2 serves as geodetic OEM GPS+GLO receiver in many productsMarch 27, 2009 © Septentrio GLONASS workshop Amsterdam 2
  3. 3. Contents  Background  FDMA in detail  GLONASS Impact on:  RF Design  Satellite Acquisition  Tracking  Positioning Algorithms  Receiver Compatibility  Summary  OutlookMarch 27, 2009 © Septentrio GLONASS workshop Amsterdam 3
  4. 4. FDMA in detail  Satellite identification division multiple access  GPS uses digital identification : one central carrier  GLONASS uses frequency identification k=-2 k=-1 k=0 k=+1 k=+2  one PRN-code for all GLONASS satellites  12 individual frequency carriers in-view  k : Frequency Number, Fn  more k-values definedMarch 27, 2009 © Septentrio GLONASS workshop Amsterdam 4
  5. 5. FDMA in detail  Consequences of FDMA  Requires wider band-pass filter  Individual filter response per carrier  Fn-SlotNR relation not defined / guaranteed  SlotNR important : antipodal system, Fn reused  users accustomed to PRN, SlotNR feels like PRN  recently 2 SV-combinations changed Fn without announcement.  Individual wavelength for each satellite  influence on RTK,PPP algorithmsMarch 27, 2009 © Septentrio GLONASS workshop Amsterdam 5
  6. 6. Impact on RF design  Current GNSS spectrumMarch 27, 2009 © Septentrio GLONASS workshop Amsterdam 6
  7. 7. Impact on RF design  band-pass filter choices : individual filtersMarch 27, 2009 © Septentrio GLONASS workshop Amsterdam 7
  8. 8. Impact on RF design  band-pass filter choices : combined GPS+GLO filtersMarch 27, 2009 © Septentrio GLONASS workshop Amsterdam 8
  9. 9. Impact on RF design  Individual carriers per SV  each GLONASS satellite excites different part of RF phase delay [rad] frequency [Hz] Filter Frequency Response  Individual group delay and phase shift per SV  pseudoranges and carrier phases will be biasedMarch 27, 2009 © Septentrio GLONASS workshop Amsterdam 9
  10. 10. Impact on RF design  RF quality determines measurement quality  linearize group delay : simplifies calibration  reduce slope of filter response  ensure temperature stability phase delay [rad]  bias around cm-level  Combined GPS+GLO RF frequency [Hz]  equal mean RF group delay for GPS+GLONASS  GPS enables calibrate GLONASS hardware delays  improved temperature stability & coherencyMarch 27, 2009 © Septentrio GLONASS workshop Amsterdam 10
  11. 11. Impact on Satellite Acquisition  Previously cumbersome...  GLONASS-M significant improvement  Fn and SlotNR relation not defined upfront  GLONASS : relation only defined in almanac  GLONASS-M : both in almanac & ephemeris  Cold Boot : acquire on Fn first  GLONASS : wait for almanac before reporting SLot  GLONASS-M : directly available  RINEX and RTCM data SlotNR based  Still one aging non-M GLONASS satellite...March 27, 2009 © Septentrio GLONASS workshop Amsterdam 11
  12. 12. Impact on Tracking  implementation of receiver Clock Jumps  odd Fn can violate integer number wavelengths  1 msec jump shifts c*10-3 / l = f*10-3 wavelenghts  spacing of 0.5625 MHz leads to 562.5 wavelengths  2 msec jumps only, or adjust phase measurements  non FDMA related  P-code not encrypted but content unknown  tracking is based on assumptions of content  during past year three changes have happened  requires firmware updates (brand indepedent)  use L2CA instead (GLONASS-M only)March 27, 2009 © Septentrio GLONASS workshop Amsterdam 12
  13. 13. Impact on Positioning Algorithms  PZ90-2 solved difference with WGS-84  Cumbersome Ephemeris format  Orbit prediction Quality still lacking  GPS-GLONASS time difference (MOSCOW UTC)  varies over time, observed 100 nanosec / month  individual wavelengths  adapt RTK and PPP algorithms  use abstract carrier phases : non-integer  pair closely space Fn : large phase residuals  RTCM/CMR generation  requires receiver clock bias wrt GLONASSMarch 27, 2009 © Septentrio GLONASS workshop Amsterdam 13
  14. 14. Inter Receiver Compatibility  RTK based on double differences  affected by mixing receiver brands or generations  Different HW design, different group delays  RF implementations vary per receiver brand  DD-biases depend on included Fn combinations  Calibrate with Initial GPS only RTK solution  determine phase shift and group delay determination for each Fn single difference  monitor time behavior to compensate T driftMarch 27, 2009 © Septentrio GLONASS workshop Amsterdam 14
  15. 15. Summary  FDMA has a significant impact on design  hardware : RF quality required  firmware : common firmware blocks not possible  Not relevant for end-user  if properly designed   GLONASS-M is a step forward  direct link between SlotNR and Fn  L2CA is future proof, avoid P  accuracy degradation acceptable  GLONASS-K significant leap  looking forward to CDMAMarch 27, 2009 © Septentrio GLONASS workshop Amsterdam 15
  16. 16. Outlook  Not meant as negative towards GLONASS  great constellation to support GPS until Galileo arrives  GPS+GLO improves DOP, height component  GPS+GLO improves availability  GPS+GLO improves integrity (redundancy)  When Galileo arrives  GLONASS will modernize to CDMA  L3 overlaps with E5 : great DualFreq GPS+GLO+GAL  fantastic quadruple constellation opportunities  next workshop on what will Compass (Beidou-2) bring...March 27, 2009 © Septentrio GLONASS workshop Amsterdam 16
  17. 17. Outlook Thanks for listening.March 27, 2009 © Septentrio GLONASS workshop Amsterdam 17

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