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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. - PowerPoint PPT Presentation
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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
MassStorage
RF Front-End
ReferenceOscillator
ADC
SampleClock
5
The Ultra Receiver
SoftwareCorrelators
TrackingLoops, DataDecoding,
ObservablesCalculations
FFT-basedAcquisition
Software Post-Processing
Digital Storage Rx
MassStorage
RF Front-End
ReferenceOscillator
ADC
Sample
Clock
Digital Storage Rx
MassStorage
RF Front-End
ReferenceOscillator
ADC
Sample
Clock
Digital Storage Rx
MassStorage
RF Front-End
ReferenceOscillator
ADC
Sample
Clock
Digital Storage Rx
MassStorage
RF Front-End
ReferenceOscillator
ADC
Sample
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 L1
L2 L2
P2 P2
C1 or P1
C1 or P1
2008 20202012 2016
Minimum IGS Receiver Requirements
8
Requirements Considerations
Pseudorange Precision Multipath Errors
L2C/L5 Rollout Timetable 2020 Discontinuation ofCodeless/Semicodeless access
9
Minimum IGS Receiver Requirements
L1 L1 L1 L1
L2 L2 L2 or L5
L2
P2 P2 or C2
P2 or C2 or C5 P2 C2
C1 or P1
C1 or P1
C1 or P1
C1 or P1
L5
C5
?
?
XX
2008 20202012 2016
10
Commercial Receivers Offerings
Topcon NET-G3
Trimble NetRS/NetR5 Septentrio PolaRx3
Leica GRX1200
11
Sample Responses to QuestionnaireMeasurement 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
ReferenceOscillator
ADC
SampleClock
SoftwareCorrelators
TrackingLoops, DataDecoding,
ObservablesCalculations
FFT-basedAcquisition
FPGA/DSP/CPU
14
Flexibility: Iridium-based Navigation on a Software Receiver Platform
~100-m geolocationerrors
15Humphreys, 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
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
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 receiver5. Revise minimum receiver requirements
according to the foregoing schedule6. 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 frequency2. Specify sample rate, quantization, type of AGC
used3. 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 data9. Recommend Galileo provide all signals to
science users