Analysis of Coast Times Upon Loss of GPS Signals for Integrated GPS/Inertial Systems

摘要

For aircraft navigation, integrating the Global Positioning System (GPS) with an inertial reference system provides a synergistic benefit because of their complementary error characteristics. GPS has good long-term accuracy while an inertial system has almost no high frequency noise. These complementary characteristics can be exploited to allow the aircraft to coast even if GPS signals are lost because of intentional or unintentional interference. In case of an interference-caused GPS outage affecting multiple aircraft, such a coasting capability would provide improved availability of Required Navigation Performance (RNP) operations, bringing significant operational benefits. For this purpose, the FAA Satellite Operational Implementation Team RNP Working Group asked the GPS/Inertial Working Group of RTCA Special Committee-159 to determine the characteristics of coasting capability for aircraft equipped with a tightly-coupled GPS/Inertial Reference System (IRS). This paper analyzes coast times for both a tightly-coupled GPS/IRS and a loosely-coupled GPS/IRS to determine if they can meet the FAA's requirements for three coasting scenarios which were considered to provide potentially significant operational benefits. The analysis is performed for a variety of conditions in terms of flight profile and user-to-satellite geometry along with a set of assumptions that the GPS/Inertial Working Group established. The results show that the tightly-coupled integration can meet the requirements for two of the FAA's three coasting scenarios, but the loosely-coupled integration cannot meet them for any of the three scenarios.