Ultra-High Performance Differential Systems: Extending Accuracy and Weak-Signal Tracking Capability

Lawrence R. Weill

Abstract:	In real-time differential GPS systems the base station transmits pseudorange corrections to a remote receiver in real time. In many applications, the base station is not subject to dynamics and can be located with an unobstructed view of all GPS satellites. However, the remote receiver is often located in a poor signal environment due to vegetative absorption or other obstructions to a clear view of the satellites. Weak signals at the remote receiver pose severe problems in obtaining satisfactory positioning performance. The major problems are: 1. Very weak signals can require an inordinate amount of time to acquire. 2. The SNR may be below the tracking threshold of the Costas-type carrier tracking loops required by the receivers. 3. The SNR also may not be sufficient to demodulate the data stream to obtain ephemeris and timing data. 4. The ability of the receiver to tolerate dynamics is severely degraded. It is not widely recognized that, in addition to pseudorange corrections, some of the high-quality signal-related information available at the base station can dramatically improve positioning performance if that information is made available to the remote receiver in real-time via a radio link. This additional information includes a frequency/time reference, the measured doppler and code phase of all satellites in view, the real-time demodulated 50 Hz data stream from each satellite, and the ephemeris data that has been collected at the base station. This paper describes how the additional information is generated, transmitted, and used by the remote receiver to mitigate weak-signal problems, thereby permitting a level of performance not obtainable by contemporary differential GPS systems. Results of analysis and computer simulations are also shown which indicate that significant performance improvements can be expected; in some cases the improvement is dramatic.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	1753 - 1762
Cite this article:	Weill, Lawrence R., "Ultra-High Performance Differential Systems: Extending Accuracy and Weak-Signal Tracking Capability," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 1753-1762.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In