Analysis of P(Y) code multipath for JPALS LDGPS ground station and airborne receivers

This paper summarizes recent multipath analysis efforts for the Joint Precision Approach and Landing System (JPALS) Local Area Differential GPS (LDGPS). Multipath is expected to be a significant error source for JPALS and, in general, multipath mitigation is achievable through siting away from potential reflectors, internal receiver processing, and antenna based techniques. Multipath data are analyzed for several receiver systems. The multipath mitigation capabilities of controlled radiation pattern antennas (CRPAs) are of particular interest since this technology will be used in the operational JPALS system. Thus, several experiments were carried out in order to evaluate CRPA receiver performance in the presence of multipath. On the ground, two candidate CRPA systems and one baseline fixed radiation pattern antenna (FRPA) system were tested at five sites with various levels of multipath. Multipath statistics show that improvements of upwards of 20% are possible with CRPA receivers in these environments. JPALS flight test data from an F-18 jet and a C-12 turboprop are also analyzed. These results show multipath errors that are generally below the Local Area Augmentation System airborne accuracy models. Comparisons between a baseline and CRPA receiver also indicate improved multipath performance on the aircraft.