Todd E. Humphreys, Cornell University

1
IGS Receiver Considerations

• Todd E. Humphreys, Cornell University
• Larry Young, JPL
• Thomas Pany, University FAF Munich

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
The Ultra Receiver
5
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
2020
2012
2016
8
Requirements Considerations
L2C/L5 Rollout Timetable
2020 Discontinuation of Codeless/Semicodeless
access
Pseudorange Precision
Multipath Errors
9
Minimum IGS Receiver Requirements
2008
2020
2012
2016
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 Calcula
tions
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
JPLs 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

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Outlook for GNSS Software Receivers

• 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

• 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 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