Test Results of a GPS/Pseudolite Precision Approach and Landing System

Alison Brown, Frank Van Diggelen, Chuck LaBerge

Abstract:	This paper describes a GPS/Pseudolite system which has been designed to provide a CAT II/III precision approach and landing capability. The system uses a Differential Carrier Ranging (DCR) positioning technique which optimally combines Pseudorange, carrier-phase and dif- ferential corrections to compute a highly precise and reliable navigation solution in real-time. The Pseudolite is used to broadcast the DCR corrections to the aircraft and also to provide an additional measurement source which improves the system redundancy and reliability. In order to use GPS for precision approach landings, the reliability and continuity of service must be consistent with current CAT II/RI requirements. This problem has been solved in the proposed system through the use of Pseudolites to augment the GPS constellation. In order to avoid the Pseudolite signal interfering with the satellite operation, the Pseudolite frequency is offset from Ll. A broad-band GPS receiver architecture has been developed that allows GPS, Pseudolite and other signals (e.g. GLONASS) to be combined in the navigation solution without any loss of precision. The DCR algorithm uses a kinematic GPS technique which requires that the carrier cycle ambiguity on each satellite must be reliably resolved in real-time. NAVSYS has developed a new rapid ambiguity search technique that optimizes the ambiguity search space for the satel- lites. This has been demonstrated to reduce the search space by a factor of 2000 over previous methods which allows the carrier cycle ambiguities to be resolved within a few seconds of acquiring the DCR corrections. Another requirement for a GPS precision approach and landing system is the requirement to detect cycle slips and other out-of-tolerance conditions (e.g. multipath errors). NAVSYS hase developed a Receiver Autonomous Integ- rity Monitoring (RAIM) algorithm that is capable of identifying these errors and, in the case of cycle slips, can correct the integer cycle ambiguity in real-time. To test the performance of the GPS/PL system, an instru- mented flight test has been performed jointly by Allied- Signal and NAVSYS. Data from both the GPS and PL signals was collected on-board an aircraft during an approach and also monitored from a ground-based refer- ence station. This data was analyzed post-test to compute the trajectory of the aircraft using the GPS and PL mea- surements. The DCR corrected kinematic GPS solution was computed and compared against the truth trajectory of the aircraft. The results of this flight test are included in the paper.
Published in:	Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993) September 22 - 24, 1993 Salt Palace Convention Center Salt Lake City, UT
Pages:	853 - 853
Cite this article:	Brown, Alison, Van Diggelen, Frank, LaBerge, Chuck, "Test Results of a GPS/Pseudolite Precision Approach and Landing System," Proceedings of the 6th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1993), Salt Lake City, UT, September 1993, pp. 853-853.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In