Real time verification of bit-cell alignment for C/A code only receivers

Jonathan Hill and William R. Michalson

Abstract:	This paper discusses how RAIM type techniques can be used to verify bit-cell alignment. In obtaining lock on a GPS satellite, it is important that the boundary between bit cells be properly identified. Given a rate of 20 Gold code periods per data bit, a misalignment by one sample introduces 1msec of delay, or approximately 300Km of pseudorange error. Obtaining bit-cell synchronization is a statistical process dependent on the carrier to noise ratio, thus bit-cell synchronization will occasionally be incorrect. Unlike authorized users, verification of bit cell alignment is difficult for C/A code only receivers. Such a GPS receiver may detect a bit-cell misalignment as an unrealistic navigation solution. Such an approach is undesirable, as it results in a navigation solution outage. It is preferred to detect such a bit-cell misalignment before a subsequent navigation solution is performed. This paper discusses how RAIM type techniques can be used to verify the initial bit cell alignment, as well as verify bit- cell alignment for a satellite before it is admitted to the group of participating satellites used to form the navigation solution.
Published in:	Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001) June 11 - 13, 2001 Albuquerque, NM
Pages:	463 - 468
Cite this article:	Hill, Jonathan, Michalson, William R., "Real time verification of bit-cell alignment for C/A code only receivers," Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001), Albuquerque, NM, June 2001, pp. 463-468.
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