Real-time GPS Signal Simulator

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.

This would provide the following benefits:

• Several labs across center would have access to a low-cost orbital, GPS constellation signal simulator.
• Projects using a GPS receiver would be able to use this GPS simulator at a very low cost of $3K compared to $30K for a playback simulator. This would enable testing of satellite formations at low cost.
• Possible additional licensing opportunities for GEONS and Navigator product lines.
• Demo examples of using GEONS and TWANG.
• Ability to quickly generate custom GPS signals for future GPS receiver research and development.

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

None of these are guaranteed paths for this specific project — TechPort itself doesn't have an "apply" button. Reaching out to the contact(s) above with a specific question is usually the fastest way to find out what's actually open.