Choosing the Best Solution to the GPS Integrity and Coverage Issues

Abstract

The FAA has stated that use of the GPS as a sole means civil aviation radionavigation system requires that a user be quickly notified of out‐of‐tolerance conditions (the “integrity” issue), and that the system provide adequate coverage even with satellite failures (the “coverage” issue). These FAA concerns have prompted numerous research studies aimed at warning GPS users of anomalous conditions and improving satellite coverage. Approaches to the integrity issue include implementation of ground‐based monitor stations to evaluate GPS signals (combined with various techniques for disseminating warnings to users), and processing of redundant data within the GPS receiver to detect anomalies and autonomously provide warning. Approaches to the coverage issue include expansion of the Department of Defense (DoD) constellation to 24 semisynchronous satellites, augmentation by dedicated geosynchronous GPS satellites, and addition of a civil GPS payload on existing geosynchronous civil weather satellites. Numerous publications have focused on technical solutions; however, selection of the best approach to resolving the coverage and integrity issues involves operational, institutional, economic, and international tradeoffs as well. This paper compares alternatives from these perspectives, using as a guide the criteria used in the Federal Radionavigation Plan for selection of a radionavigation system mix.