Evaluation of Assisted GPS (AGPS) in Weak Signal Environments Using a Hardware Simulator

M.D. Karunanayake, M.E. Cannon and G. Lachapelle

Abstract:	The E-911 mandate from the Federal Communication Commission requires a mobile 911 caller location to be established for 67 percent of calls to within 50 meters and 95 percent of calls to within 150 meters for wireless handset-based solutions. High Sensitivity (HS) GPS receivers, once initialized outside, can acquire and track GPS signals in weak signal environments. This is not necessary with an Assisted GPS (AGPS) receiver where assistance is provided via a cellular network so acquisition can be done at lower signal strengths. The focus of this paper is to investigate AGPS receiver performance from two perspectives. The first is to determine the acquisition and tracking threshold of an AGPS receiver. The second is to investigate the effect of timing and assistance data on AGPS receiver acquisition performance under weak signal conditions. A SiRFLocTM evaluation kit, developed by SiRF Technologies Inc., is used to investigate AGPS receiver performance. Tests are conducted using the Spirent GSS6560 Hardware Simulator and results are analyzed in terms of Time-To- First-Fix (TTFF) and position accuracy. It was found that an AGPS receiver provides a 13 dB improvement in acquisition sensitivity over an HS receiver. The accuracy of timing, the initial reference position and the associated uncertainty of the initial position all have an impact on the TTFF.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	2416 - 2426
Cite this article:	Karunanayake, M.D., Cannon, M.E., Lachapelle, G., "Evaluation of Assisted GPS (AGPS) in Weak Signal Environments Using a Hardware Simulator," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 2416-2426.
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