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IGS Receiver Considerations

Todd E. Humphreys, Cornell University Larry Young, JPL Thomas Pany, University FAF Munich. IGS Receiver Considerations. 2008 IGS Workshop, Miami Beach FL. Opportunity: New GNSS Signals.

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IGS Receiver Considerations

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  1. Todd E. Humphreys, Cornell University Larry Young, JPL Thomas Pany, University FAF Munich IGS Receiver Considerations 2008 IGS Workshop, Miami Beach FL

  2. Opportunity: New GNSS Signals (Fig. 1 of Wallner et al., "Interference Computations Between GPS and Galileo," Proc. ION GNSS 2005)

  3. Overview • IGS receiver characteristics: Ultra, Super, Minimum • Commercial Receiver Outlook • Software Receiver Outlook • Recommendations

  4. Digital Storage Rx RF Front-End ADC MassStorage ReferenceOscillator SampleClock The Ultra Receiver

  5. Digital Storage Rx Digital Storage Rx Digital Storage Rx Digital Storage Rx Software Post-Processing RF Front-End RF Front-End RF Front-End RF Front-End ADC ADC ADC ADC FFT-based Acquisition Tracking Loops, Data Decoding, Observables Calculations MassStorage MassStorage MassStorage MassStorage Software Correlators ReferenceOscillator ReferenceOscillator ReferenceOscillator ReferenceOscillator SampleClock SampleClock SampleClock SampleClock The Ultra Receiver

  6. The Super Receiver • Tracks all open signals, all satellites • Well-defined, publicly disclosed measurement characteristics (phase, pseudorange, C/No) • RINEX compliant • Completely user reconfigurable, from correlations to tracking loops to navigation solution • Internal cycle slip mitigation/detection • Up to 50 Hz measurements • Internet ready; signal processing strategy reconfigurable via internet • Low cost

  7. Minimum IGS Receiver Requirements 2008 2012 2016 2020

  8. Requirements Considerations L2C/L5 Rollout Timetable 2020 Discontinuation of Codeless/Semicodeless access Pseudorange Precision Multipath Errors

  9. Minimum IGS Receiver Requirements 2008 2012 2016 2020 X X

  10. Commercial Receivers Offerings Septentrio PolaRx3 Trimble NetRS/NetR5 Leica GRX1200 Topcon NET-G3

  11. Sample Responses to Questionnaire Measurement intervals defined? Tracking loop parameters configurable or disclosed? Firmware updates deliverable via internet? Baseband software available for licencing? Recommended receiver and approximate list price (no antenna):

  12. Outlook for Commercial Receivers • Bad: • Some vendors unwilling to disclose measurement characterization • Problems in past with proprietary output formats (2 year wait!) • Uneven C/N0 reporting on some devices • No support for exotic tracking techniques • Limited reconfigurability • IGS has little leverage • Good: • Market trend is to track all available signals, all satellites • Internet ready • Some vendors offer increasing reconfigurability • All top vendors provide near-optimal standard tracking • Rugged, stable, reliable platforms

  13. Software GNSS Receiver Front End FPGA/DSP/CPU RF Front-End ADC FFT-based Acquisition Tracking Loops, Data Decoding, Observables Calculations Software Correlators ReferenceOscillator SampleClock

  14. Flexibility: Iridium-based Navigation on a Software Receiver Platform ~100-m geolocation errors

  15. Cornell GRID Receiver(GNSS Receiver Implementation on a DSP) Cornell “GRID” Dual-Frequency Software-Defined GNSS Receiver • Supports 72 L1 C/A channels • FFT-based acquisition down to C/N0 = 32 dB-Hz • Carrier tracking down to C/N0 = 25 dB-Hz • Version 2: Dual-frequency (L1/L2C) with improved scintillation robustness • Completely software reconfigurable Humphreys, T. E., B. M. Ledvina, M. L. Psiaki, and P. M. Kintner, Jr., "GNSS receiver implementation on a DSP: Status, challenges, and prospects," Proc. 2006 ION GNSS Conf., Institute of Navigation, 2006

  16. GNSS Software Receiver at University FAF Munich & IFEN GmbH • L1, L2, L5 front-end • 13 MHz bandwidth at each frequency • Multiple CPU cores for parallel processing • Tracks all-in-view civil GPS, SBAS, and Galileo • 1 kHz max measurement output rate • Completely software reconfigurable

  17. JPL’s TOGA Instrument(Time-shifted, Orthometric, GNSS Array) • L1, L2, L5 front-end • Electronically-steered antenna array • Multiple FPGAs for parallel processing • Buffer memory for near-realtime or offline processing • Completely software reconfigurable

  18. Outlook for GNSS Software Receivers • Bad: • Only JPL currently supports P(Y) tracking • Have not been thoroughly evaluated against traditional receivers • Good: • Complete reconfigurability • Complete transparency • Support for exotic tracking strategies • Theoretical performance equal or better than commercial receivers • Unknowns: • Who will build platforms? • Who will maintain software? • ACs? • Commercial provider? • Price?

  19. Recommendations (1/2) • Study the effects of long-delay multipath by comparing (P1,P2) with (C1,C2) measurements from same SV • Compare software receiver and traditional receiver performance via signal simulator and field tests • Demand from receiver vendors either (1) detailed measurement description, or (2) adoption of a standard measurement technique (e.g., JPL technique) • Consider an IGS-sponsored software receiver • Revise minimum receiver requirements according to the foregoing schedule • Any comment on US proposal to discontinue access to semicodeless P(Y) tracking? If not, then suggest “no comment.”

  20. Recommendations (2/2) • Any comment on US proposal to discontinue access to semicodeless P(Y) tracking? If not, then suggest “no comment.” • Establish an IGS format for exchange of data among software receivers • Specify BW and carrier frequency • Specify sample rate, quantization, type of AGC used • Samples must be time tagged with an accuracy < 10 usec and sample clock must have Allan deviation < 10e-9 for T = 1 to 100 sec (shorter time scales commensurate) • Specify IF of sampled data • Recommend Galileo provide all signals to science users

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