Optimizing the Decision Rule of a GPS Integrity Monitoring System for Improved Availability

Résumé du livre

The Global Positioning System, which was created by the United States Department of Defense specifically for guiding munitions, has disseminated into many applications of the present. Using a differential, ground based augmentation scheme has enabled GPS guidance to be used for the ultra-safety requisite use of landing aircraft. The civil incantation of this project is called LAAS, for Local Area Augmentation System. The military desired a comparable system for their use, and has instituted the JPALS program, for Joint Precision and Approach Landing System. The object is to deliver an integrity monitor to satisfy the stringent requirements of difficult military operation. Although the distinction of emphasis might seem to be on the inherent danger of physical conflict, since the landing platform is expected to be distant from any combat, it is actually the electro-magnetic conflict which takes precedence in this thesis. The JPALS land-based, or sea-based, Integrity Monitor must be designed to endure radio frequency interference, RFI. The potential of RFI to undermine the operation of a landing system is quite real. The intrinsic obligation of an Integrity Monitoring System is to bound the errors associated with the guidance being provided. To this end, the system must determine if any of measurements are faulty, and if those fault(s) indicate the presence of a potentially hazardous position error. Hardware and software can be used to mitigate the impact of radio frequency interference to a GPS based landing system. Beam-steering antennas can be used to emphasize the satellites' signals, and to simultaneously deemphasize a jamming source. The focus of this thesis is in the software algorithms. How can we enhance the performance of our system in its robustness to interference, by optimizing the decision rule it uses to exclude satellites, and receivers, thereby maximizing the amount of useable information, and minimizing the error limits that are broadcast to the approaching aircraft.