# Presentation: 665615

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

-   Larry Young, JPL
-     Thomas Pany, University FAF Munich

- 2008 IGS Workshop, Miami Beach FL

- IGS Receiver Considerations

## Opportunity: New GNSS Signals

- (Fig. 1 of Wallner et al., "Interference Computations Between GPS and Galileo," Proc*. ION GNSS 2005*)

## Overview

- IGS receiver characteristics:
-    Ultra, Super, Minimum
- Commercial Receiver Outlook
- Software Receiver Outlook
- Recommendations

## 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

| L1 |  |  | L1 |
| --- | --- | --- | --- |
| L2 |  |  | L2 |
| P2 |  |  | P2 |
| C1 or P1 |  |  | C1 or P1 |
|  |  |  |  |
|  |  |  |  |
|  |  |  |  |
|  |  |  |  |

*2008*

*2020*

*2012*

*2016*

## Requirements Considerations

**Pseudorange Precision **

**Multipath Errors **

**L2C/L5 Rollout Timetable **

**2020 Discontinuation of**
**Codeless/Semicodeless access **

## 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 |
|  |  |  | ? |
|  |  |  | ? |

- X

- X

*2008*

*2020*

*2012*

*2016*

## Commercial Receivers Offerings

**Topcon NET-G3 **

**Trimble NetRS/NetR5 **

**Septentrio PolaRx3 **

**Leica GRX1200 **

## 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):

## 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

## Software GNSS Receiver

- Front End

- RF Front-End

- ReferenceOscillator

- ADC

- SampleClock

- Software
- Correlators

- Tracking
- Loops, Data
- Decoding,
- Observables
- Calculations

- FFT-based
- Acquisition

- FPGA/DSP/CPU

## Flexibility: Iridium-based Navigation on a Software Receiver Platform

**~100-m geolocation**
**errors**

## 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

- 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)

**Notes:**
I know that we who aspire to being academics should hew to theory and not get too excited about devices, but I’ll confess that I get excited about this box, and I devoted a great deal of time to developing it while at Cornell.  
It’s capable even compared to receivers who use dedicated GPS processing chips, and its flexibility means that it can be tailored for use in novel GPS-based applications.  

You can think of it as a powerful platform for ionospheric, etc, research

## GNSS Software Receiver at University FAF Munich & IFEN GmbH

- 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) 

- 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

## Good:
Complete reconfigurability
Complete transparency
Support for exotic tracking strategies
Theoretical performance equal or better than commercial receivers

- 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?

## 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