Achieving GPS Integrity and Eliminating Areas of Degraded Performance

There are two concerns regarding the civil use of the Global Positioning System (GPS). The first is “integrity,” which is the possibility that GPS transmits an erroneous navigation signal to the user. A malfunction of the atomic frequency standard in the satellite is regarded as a possible integrity problem. The second concern is the areas of degraded performance. Although four satellites may be visable, because of poor satellite geometry the accuracy of navigation can be severely degraded for a short period of time. This paper discusses an approach to the solution of each of these two issues. It is shown that a communications type geostationary satellite is a common element to the solution of both concerns. Also common to both is a network of integrity monitoring and control stations. The paper discusses a system to cover the North American continent and also how it might be expanded to become worldwide.