GPStream: A Low Bandwidth Architecture to Deliver or Autonomously Generate Predicted Ephemeris

Eric Derbez, Rich Lee

Abstract:	Assisted GPS is becoming a mainstream GPS architecture choice in mobile deployments to improve the time to first fix (TTFF) and to better exploit a receiver´s sensitivity. There are various methods of providing assistance data to the mobile device requiring varying degrees of real-time connectivity and data passed across a communications link. The architecture described here reduces both the real-time connectivity and data requirements compared to other techniques. By performing numerical integration on board a PND or wireless PDA, the GPStream architecture allows a client to use either the: predicted GPS (PGPS) mode to receive a 2KB payload to generate ephemeris for a week; or the self-assist GPS (SAGPS) mode to generate its own 1-3 day prediction given previous ephemerides demodulated from the sky. We first start by describing the architecture & modeling done in the GPStream software. Then we proceed to describe how errors in orbit prediction impact the URE and what trade-offs are made in the PGPS/SAGPS payload and modeling. Finally, we discuss orbit error analysis of PGPS/SAGPS synthetic ephemeris versus International GNSS Service (IGS) data, and discuss position fix accuracy through actual fix data and more extensively through simulations across number of SVs & geometry.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	1258 - 1264
Cite this article:	Derbez, Eric, Lee, Rich, "GPStream: A Low Bandwidth Architecture to Deliver or Autonomously Generate Predicted Ephemeris," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 1258-1264.
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