A risk analysis framework on GPS User Range Accuracy

Accuracy is a major concern in Global Positioning System (GPS), and User Range Accuracy (URA) is a statistical indicator of the ranging accuracy for satellites. URA is obtainable from the satellite´s signal in space (SIS); its computation depends heavily on the ground segment. The risk considered here is the failures from the GPS control segment that cause a satellite´s URA to exceed the requirement, hence excluding the satellite from being used in the position solutions, and ultimately degrading system availability. The corresponding risk analysis is complex and a framework is presented here as one approach to looking at the problem. A hypothetical example is applied to demonstrate the framework from an RMA (reliability, maintainability, and availability) specialty engineer´s point of view, where the requirements, algorithms, and failures analyses are integrated together.