IGS Receiver Considerations
Todd E. Humphreys, Cornell University
Larry Young, JPL
Thomas Pany, University FAF Munich

Opportunity: New GNSS Signals
IGS receiver characteristics:
Ultra, Super, Minimum
Commercial Receiver Outlook
Software Receiver Outlook
The Ultra Receiver

The Ultra Receiver
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

Minimum IGS Receiver Requirements
Requirements Considerations
Minimum IGS Receiver Requirements
Commercial Receivers Offerings
Sample Responses to Questionnaire
Outlook for Commercial Receivers
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
Software GNSS Receiver
Flexibility: Iridium-based Navigation on a Software Receiver Platform
Cornell GRID Receiver (GNSS Receiver Implementation on a DSP)
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

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

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

Outlook for GNSS Software Receivers
Complete reconfigurability
Complete transparency
Support for exotic tracking strategies
Theoretical performance equal or better than commercial receivers
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.

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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