The Case for Both RAIM and GIC Working Together: the Ultimate Solution to the GPS Integrity Problem

R. Grover Brown

Abstract:	GPS integrity has been studied intensively during the past few years. Two rather distinct approaches to the problem have evolved during this period. They are (1) Receiver Autonomous Integrity Monitoring (RAIM) and (2) the ground monitoring approach or GPS Integrity Channel (GIC). By and large, these have been considered as competing schemes thus far. It is suggested here that this need not be the case. Quite to the contrary, the two methods are complementary, and they can and should work together to provide the ultimate solution to the GPS integrity problem. The GIC scheme proposed by the GIC Working Group of RTCA Special Committee 159 will provide the user with quantitative measures of the GPS satellites' range errors as observed by the ground monitors. However, applying the corrections supplied by GIC in the navigation solution would involve combining the navigation and integrity functions, and many in the navigation community feel uncomfortable with mixing the two functions. This is where RAIM comes into play. The proposed GIC system also has the potential of providing ranging capability on the two geostationary satellites. If these additional ranging signals were made available, this would correct an availability weakness that exists in RAIM, and it would make it possible to use RAIM effectively 100 percent of the time, in CONUS at least. The user could then use , the pseudorange corrections supplied by GIC in the navigation solution and still get an independent integrity check with RAIM. The improved solution thus obtained would make it possible to meet the 100 m nonprecision approach goal. RAIM and GIC working together as just described would, in effect, provide a "double padlock" on GPS integrity. In order to accomplish this, however, ranging capability must be designed into GIC, and this is the main message of this paper
Published in:	Proceedings of the 1989 National Technical Meeting of The Institute of Navigation January 23 - 26, 1989 San Mateo, CA
Pages:	53 - 55
Cite this article:	Brown, R. Grover, "The Case for Both RAIM and GIC Working Together: the Ultimate Solution to the GPS Integrity Problem," Proceedings of the 1989 National Technical Meeting of The Institute of Navigation, San Mateo, CA, January 1989, pp. 53-55.
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