A Novel Approach to Enhancing the Sensitivity of C/A Code GPS Receivers

P. A. Dafesh and T. Fan

Abstract:	The availability of a GPS navigation solution is limited by a receiver's ability to acquire the GPS signal in the presence of foliage attenuation, in-building attenuation and multi-path. All of these conditions make it desirable to exploit the available GPS signal strength to its fullest. One of the factors limiting the acquisition of a GPS signal is the processing gain that can be obtained under these conditions. This is especially critical for in-building and urban applications of GPS receivers. Usually, it is desirable to maximize the coherent integration period for a GPS receiver, which is typically limited to the data bit period. For the C/A code, having a 1 ms repeat period, the processing gain benefit of integrating over 20 ms can only be realized if the bit boundaries are known. In acquisition of the P(Y)-code signal, the non-repetitive nature of the code, and the coherency of the code to the GPS data message will precisely determine the bit boundaries relative to the start of the integrate and dump period. For the C/A code, these boundaries are known only to within some number of 1 ms C/A code repeat periods. As a result, the start of an integration period can be off by as much as 10 ms from the start of a data boundary if a 20 ms integration period is used. Consequently, the acquisition process is usually limited to small integration periods or increased losses due to lack of data boundary coherency prior to carrier tracking. While wireless-assisted GPS aiding has been proposed to enable the determination of bit boundaries for application to this problem, the reliance on the wireless infrastructure makes this approach undesirable due to the need to interface with multiple wireless standards all over the world. This paper describes a novel technique to determine the detection of the GPS bit boundaries during the acquisition process. The technique mitigates the effect of losses due to unknown bit boundaries prior to carrier tracking and does not rely on wireless assisted GPS techniques. Thus the approach provides enhanced receiver acquisition sensitivity for in-building applications where wireless network assistance is unavailable. The work describes the implementation and potential benefits of this approach during acquisition prior to carrier loop pull-in.
Published in:	Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001) June 11 - 13, 2001 Albuquerque, NM
Pages:	481 - 488
Cite this article:	Dafesh, P. A., Fan, T., "A Novel Approach to Enhancing the Sensitivity of C/A Code GPS Receivers," Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001), Albuquerque, NM, June 2001, pp. 481-488.
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