GPS performance monitoring results for operational applications including B-RNAV

David Walsh, Gary Brodin, Michael Daly, Mark Denney and Steve Griffin

Abstract:	UK Air Traffic Services are subject to approval by the CAA Safety Regulation Group (SRG). Approval of existing systems is granted once the regulator is assured that the systems employed meet safety requirements. GPS, as a US military system, presents difficulties in gaining safety assurances from the provider using traditional regulatory means. Therefore the regulator is seeking other means to seek information necessary to assist in the approval of GPS-based air traffic services. One approach is to monitor the GPS signal-in-space performance in respect to the specific needs of air traffic service (i.e. B-RNAV), and also in respect of the GPS performance specification itself. With regards to safety, of particular concern are GPS anomalies which could have safety related consequences in the aviation domain. GPS anomalies have been reported by institutions in the past and in CAA MORs. This paper firstly describes the GPS performance monitoring system which has been designed and implemented by the CAA ISN for the SRG. The requirements for the GPS signal-in-space monitoring system were established through analysis of GPS performance specifications, B-RNAV service application requirements, and reported GPS anomalies. Over 300 possible tests on the GPS Signal In Space were identified. The paper concentrates on the SPS Predictable Accuracy tests in the post-Selective Availability period. The Standard Positioning Service (SPS) test methodology is briefly discussed. Four different receiver types are used including certified avionics receivers (TSO C-129a). The monitoring system was particularly designed to detect “invisible” anomalies and to identify the source of the anomaly. The monitoring system has been exhaustively tested and nearly 2 years of data has been logged. This paper describes the results of the GPS monitoring system for March to August 2001. The results show actual GPS performance compared to expected performance over this period as experienced from Leeds, UK. The results shown are for predictable accuracy as defined in the SPS standard. The predictable accuracy results are also analysed with respect to the new suggested SPS standards.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	75 - 80
Cite this article:	Walsh, David, Brodin, Gary, Daly, Michael, Denney, Mark, Griffin, Steve, "GPS performance monitoring results for operational applications including B-RNAV," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 75-80.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In