Integration and Testing of a Wide-Band Airport Pseudolite
The paper provides initial results of a series of flight tests conducted using the LAAS Test Prototype/Airport Pseudolite system.
Proposed Airport Pseudolite Signal Specification for GPS Precision Approach Local Area Augmentation Systems
The availability and continuity of accuracy and integrity are major concerns for GPS-based precision approach and landing systems without augmentation. Thus, following the lead of the FAA baseline Local Area Augmentation System (LAAS) architecture that includes pseudolites, RTCA Special Committee 159 Working Group 4a for GPS/Precision Landing Guidance has set up an Airport Pseudolite (APL) subgroup. The purpose of this subgroup is to develop LAAS pseudolite standards. This subgroup is responsible for trade studies necessary for the development of an APL signal structure. This development is well underway, starting with a set of basic assumptions to be considered in that development. Minimum performance criteria for a viable pseudolite signal structure are also being established. This paper presents these basic assumptions to be considered and the resulting minimum performance criteria for the APL signal structure. Then, the details of the proposed APL signal specification currently under review that meets those criteria are described. Also, the analytical results that justify the proposal against the defined considerations and minimum performance requirements are presented.
Performance Evaluation of On-Airport Local Area Augmentation System Architectures
Recently there has been growing demand for a Category III precision landing system architecture which is completely contained on airport property. In response, Stanford is exploring different Local Area Augmentation System (LAAS) architectures and evaluating their performance. To maximize this performance, the architectures incorporate information from a variety of sources, including code-centered carrier techniques, satellite motion, and airport pseudolites (APLs). In addition to using APLs as additional ranging sources, a new concept was developed for positioning with pseudolites. The new concept involves using the differential carrier phase between a pair of pseudolites. This differential carrier phase provides an additional observable that can improve the accuracy of GPS positioning. The surfaces of constant differential phase are hyperbolic. In the far field however, the system approximates an angular based system such as the Instrument Landing System (ILS). For example, if the two pseudolites are located at the top and bottom of a tower near the aim point, the phase difference measurement at the aircraft is analogous to the glideslope measurement for ILS. Although there is an integer cycle ambiguity associated with the differential carrier phase measurement, this ambiguity can be resolved when the aircraft is on long final approach. At this distance, the position difference between integer candidates is so large that differential code phase positioning can isolate the correct integer. Several APL configurations have been explored through computer simulation. The effects of both additional ranging sources and APL differential carrier phase measurements are incorporated into the simulation. Also incorporated are the effects of satellite motion and codecentered carrier smoothing. The resulting performance is due to a combination of these effects. In addition to simulation, ground experiments and flight tests have been performed. The results of simulation and flight testing are presented, and the navigation performance of these architectures is assessed.