An efficient computational method for horizontal/vertical exclusion level as part of Fault Detection and Exclusion implementation

L. Lupash

Abstract:	It is well known that the fault detection and exclusion (FDE) function in a GPS receiver is required for primary means GPS navigation. The determination of the horizontal/vertical exclusion level (HEL/VEL) is a part of the FDE function in a GPS receiver. While the computation of horizontal/vertical protection level (HPL/VPL) is well represented in technical literature, relatively few brief references are known to be presented in open literature on HEL/VEL computation. The common known HEL/VEL computation is based on the determination of HPL/VPL quantities for subsets of satellite geometry (or measurements) when one satellite is eliminated at one time from the available satellite list, and the HEL/VEL value is taken as the maximum over all determined HPL/VPL quantities. This approach is computationally inefficient especially when the number of available navigation satellites (or measurements) is large. On the other hand, this paper presents a new efficient algorithm for the computation of HEL/VEL when a snapshot RAIM implementation is considered. The basic idea is to reduce the computational burden by using at maximum the information already known from the HPL/VPL determination. By using a known matrix identity when one measurement is eliminated at one time from the original measurement matrix the HEL/VEL quantities can be determined more efficient. The computational saving in flops is substantial, dependent on the total number of measurements used. It is estimated that the reduction of computational effort is up to 30% when is compared with the classical (brute-force) implementation. Test results confirm the efficiency of the proposed method. Finally, the computation of HPL and HEL quantities are used to determine the fault detection and fault exclusion availability performance of the Trimble’s military receivers in accordance to RTCA/DO- 229 and GRAM-S requirements [3], [13].
Published in:	Proceedings of the 2003 National Technical Meeting of The Institute of Navigation January 22 - 24, 2003 Disneyland Paradise Pier Hotel Anaheim, CA
Pages:	133 - 141
Cite this article:	Lupash, L., "An efficient computational method for horizontal/vertical exclusion level as part of Fault Detection and Exclusion implementation," Proceedings of the 2003 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2003, pp. 133-141.
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