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

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 The Ultra Receiver Digital Storage Rx Mass Storage RF Front- End Reference Oscillator ADC Sample Clock

5 The Ultra Receiver Software Correlators Tracking Loops, Data Decoding, Observables Calculations FFT-based Acquisition Software Post-Processing Digital Storage Rx Mass Storage RF Front- End Reference Oscillator ADC Sampl e Clock Digital Storage Rx Mass Storage RF Front- End Reference Oscillator ADC Sampl e Clock Digital Storage Rx Mass Storage RF Front- End Reference Oscillator ADC Sampl e Clock Digital Storage Rx Mass Storage RF Front- End Reference Oscillator ADC Sampl e Clock

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 L1 L2 P2 C1 or P Minimum IGS Receiver Requirements

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

9 Minimum IGS Receiver Requirements L1 L2 L2 or L5L2 P2P2 or C2 P2 or C2 or C5 P2 C2 C1 or P1 L5 C5 ? ? X X

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

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 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 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

13 Software GNSS Receiver Front End RF Front- End Reference Oscillator ADC Sample Clock Software Correlators Tracking Loops, Data Decoding, Observables Calculations FFT-based Acquisition FPGA/DSP/CPU

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

15 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 ION GNSS Conf., Institute of Navigation, 2006 Supports 72 L1 C/A channels FFT-based acquisition down to C/N 0 = 32 dB-Hz Carrier tracking down to C/N 0 = 25 dB-Hz Version 2: Dual-frequency (L1/L2C) with improved scintillation robustness Completely software reconfigurable Cornell “GRID” Dual-Frequency Software-Defined GNSS Receiver Cornell GRID Receiver (GNSS Receiver Implementation on a DSP)

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

19 Recommendations (1/2) 1. Study the effects of long-delay multipath by comparing (P1,P2) with (C1,C2) measurements from same SV 2. Compare software receiver and traditional receiver performance via signal simulator and field tests 3. Demand from receiver vendors either (1) detailed measurement description, or (2) adoption of a standard measurement technique (e.g., JPL technique) 4. Consider an IGS-sponsored software receiver 5. Revise minimum receiver requirements according to the foregoing schedule 6. Any comment on US proposal to discontinue access to semicodeless P(Y) tracking? If not, then suggest “no comment.”

20 Recommendations (2/2) 7. Any comment on US proposal to discontinue access to semicodeless P(Y) tracking? If not, then suggest “no comment.” 8. Establish an IGS format for exchange of data among software receivers 1. Specify BW and carrier frequency 2. Specify sample rate, quantization, type of AGC used 3. 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) 4. Specify IF of sampled data 9. Recommend Galileo provide all signals to science users