Analysis of P(Y) code and carrier multipath for JPALS ship and airborne receivers

The Land-Based Joint Precision Approach and Landing System (JPALS) is a military differential landing system similar in architecture to the civil Local Area Augmentation System (LAAS) [1]. Sea-Based JPALS is a relative kinematics system that utilizes carrier phase based solutions for the required accuracy of landing on an aircraft carrier. Code multipath is expected to be a significant error source for both systems while carrier multipath is of particular concern for the Sea-Based system and its stringent availability and accuracy requirements [2]. To develop validated requirements for the ship reference stations and the airborne platforms, multipath experiments were conducted in a static environment with an F/A-18 air frame, and also onboard an aircraft carrier. In all experiments, dual-frequency P(Y) code and carrier phase data were collected. This paper describes the experimental methodology and presents results form the tests conducted. The aircraft static tests show multipath errors of up to 1 m in P(Y) code, and are matched well by simulations. Superimposing realistic flight profiles on these results illustrates how multipath errors are randomized by aircraft attitude motions, resulting in a reduction of multipath RMS by up to 30%. Outdoor multipath tests were conducted onboard the aircraft carrier USS Eisenhower with several day of static dock-side testing to characterize the aircraft carrier environment for code and carrier multipath. Experiments were also conducted while the ship was at sea in order to assess the effect of the sea-state on multipath. In addition to code multipath, a double difference phase multipath ovservable was also computed. Receiver tracking performance and multipath analysis results are presented.