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Center Independent Research & Development: GSFC IRAD

Real-time GPS Signal Simulator

Completed Technology Project

Project Introduction

With a minimal FTE investment and no additional procurement funds, the development of a low fidelity orbital GPS Signal simulator would is possible.  

This IRAD leverages existing Navigator software, MATLAB simulation tools, Goddard Enhanced Onboard Navigation System (GEONS), and TDRSS Waveform and Noise Generator (TWANG).  A small amount of work is required to integrate these existing products together to develop a GPS signal simulator.

The existing GEONS API interface will be used to provide the following information about the various GPS transmitting satellites: GPS satellite signals available, signal power estimates, signal delays, and signal frequencies.

An existing low-fidelity data bit generator will be leveraged that ingests GPS ephemeris/almanac data and produces the data bit stream that is generated by the GPS satellites.  The software for the data bit generator is to be updated to conform more closely to the GPS data bit structure.

The GPS Satellite’s signal information (power, Doppler, and delay) and raw data bit message would be fed into either TWANG, or part of Navigator’s software would be repurposed for this application.  Raw RF data would be output into a file, or onto a TCP socket. The recorded raw RF data would be replayed through our existing software receiver for initial testing.

Existing Universal Software Radio Peripherals (USRPs) in the lab would transmit the raw RF data to one of the Formation Flying Test Bed’s (FFTB) GPS receivers for testing, or into a separate USRP and then into the software receiver for hardware testing.

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