Inertially-aided GPS Signal Re-acquisition in Poor Signal to Noise Environments and Tracking Maintenance through Short Signal Outages

Paul D. Groves and Daniel C. Long

Abstract:	The main subject of this paper is using INS aiding to reacquire GPS signals in poor signal to noise environments. Conventional signal acquisition requires a much stronger signal to noise environment than signal tracking. This is because a large number of code phase and Doppler shift combinations have to be searched, so measurement data for each combination can only be accumulated for a short period, typically 1 ms, requiring a relatively high signal to noise. For re-acquiring signals in a well calibrated INS/GPS system, the user-satellite line of sight velocity is known and the approximate code phase can be obtained from the integrated navigation solution and the known satellite position. Consequently, much fewer combinations need be searched, enabling data to be accumulated for much longer, allowing re-acquisition in much poorer signal to noise environments. A theoretical analysis is backed up by simulation results showing that reacquisition can operate at similar signal to noise levels to code tracking C/N0 levels down to about 8-10 dB-Hz. The paper also describes using the integrated navigation solution to maintain tracking through brief GPS signal outages in a tightly-coupled INS/GPS system, matching what is an implicit process in deep INS/GPS. This work is relevant to navigation in poor GPS signal to noise environments such as indoors, in some urban canyons and in the presence of jamming or interference. It is also relevant where frequent short-term blockage of GPS signals is a problem, such as navigation in urban areas and highly dynamic applications.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	2408 - 2417
Cite this article:	Groves, Paul D., Long, Daniel C., "Inertially-aided GPS Signal Re-acquisition in Poor Signal to Noise Environments and Tracking Maintenance through Short Signal Outages," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 2408-2417.
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