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

GPS integrity has been studied intensively during the past few years. Two rather distinct approaches to the problem have evolved during this period: (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, but 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 integrity information via two geostationary satellites. It is suggested here that the GIC system should be designed such that the user will be able to range on the geostationary satellites, as well as receive integrity information from them. The additional ranging capability will then enhance RAIM and make it possible to have RAIM available 100 percent of the time.