Mitigation of the Near-Far Problem by Successive Interference Cancellation

Premal H. Madhani, Penina Axelrad, Kent Krumvieda and John Thomas

Abstract:	Accuracy, availability, and continuity of service for certain high precision applications cannot be met by Global Positioning System (GPS) alone. An example is the precision approach and landing of aircraft. Ground based transmitters called pseudolites have been proposed for GPS augmentation to meet these critical requirements. A large variation in the range between the pseudolite transmitter and the receiver causes large fluctuations in the received signal power. In the region near the pseudolite, the pseudolite signals can be orders of magnitude stronger than the satellite signal power, making it difficult for the receiver to simultaneously detect the satellite signals. This is called the near-far problem. Many of the techniques proposed or implemented at present require a modification of the receiver front end or the pseudo random noise code structure. This paper describes the application of a signal processing technique, known as successive interference cancellation (SIC), that makes the receiver immune to the near-far problem without modifications to the receiver front end or the signal structure. In addition to the direct signal from the pseudolite, strong pseudolite multipath signals can also lead to degradation in receiver performance in a near-far scenario. A new technique, which we call reverse SIC (RSIC), is also developed and implemented to estimate and remove the pseudolite multipath signals. This results in reduced multiple access interference for weak satellite signals in a near-far environment and improved range measurement to the pseudolite. The new architecture is implemented on simulated and experimental near-far data sets. The results are compared to a conventional detector showing improvements in acquisition and tracking performance in the presence of a strong pseudolite.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	148 - 154
Cite this article:	Madhani, Premal H., Axelrad, Penina, Krumvieda, Kent, Thomas, John, "Mitigation of the Near-Far Problem by Successive Interference Cancellation," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 148-154.
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