Coarse Time Navigation: Equivalence of Algorithms and Reliability of Time Estimates

K. Muthuraman, J. Brown, M. Chansarkar

Abstract:	Methods that rely on estimating time-of-week (TOW) information, in addition to user position and receiver clock bias, rather than decoding TOW from live signals are commonly referred to as coarse time navigation algorithms. A priori information required for these algorithms include valid ephemeris, an approximate user position and TOW. Inputs to these algorithms are sub-ms pseudorange measurements. When sub-ms pseudorange measurements are used to resolve unknowns, integer-millisecond errors across measurements can lead to potential blunders. Two possible solutions are found in the literature to address this issue: Lannelongue & Pablos (1998) and van Diggelen (2002). One of the novel contributions of this paper is to clearly show that, under most practical conditions (range error less than 75 km), these two methods collapse down to be identical, through clear mathematical models. Further, this paper also evaluates the possibility of starting with coarse time parameters to resolve time within fine time standards (10 ms or better) by excluding degraded solutions through integrity checks. The analysis is presented using statistics gathered under different signal power and satellite geometry conditions. Results indicate that the proposed integrity checks are reliable in detecting solutions with a time error of 10 ms or more under nominal signal conditions. However, under weak signal conditions (25 dB-Hz) 5-15% of the filtered solutions still had an error larger than the desired 10 ms.
Published in:	Proceedings of the 2012 International Technical Meeting of The Institute of Navigation January 30 - 1, 2012 Marriott Newport Beach Hotel & Spa Newport Beach, CA
Pages:	1115 - 1138
Cite this article:	Muthuraman, K., Brown, J., Chansarkar, M., "Coarse Time Navigation: Equivalence of Algorithms and Reliability of Time Estimates," Proceedings of the 2012 International Technical Meeting of The Institute of Navigation, Newport Beach, CA, January 2012, pp. 1115-1138.
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