Mitigation of Narrow-band Interference on Software Receivers Based on Spectrum Analysis

Z. Jiang, C. Ma and G. Lachapelle

Abstract:	Over the years, many GPS RFI mitigation methods have been developed and their effectiveness has been tested and quantified. However, most of these methods were implemented and tested using conventional hardware receivers. With the rapid development of computer technologies, the signal processing computational load is becoming less of a concern, and thus it becomes feasible to develop and test new interference mitigation methods based on software receivers and modern digital signal processing techniques. In this paper, a narrow band RFI mitigation method based on spectrum analysis is fully discussed and tested, using a newly developed software receiver. Although such a frequency domain analysis-based interference mitigation method has already been addressed by some researchers, for example, Peterson et al [1996] and Cutright et al [2003], many implementation issues, such as the determination of the detection threshold for different kinds of interference and different interference levels, the impact of narrow band interference and the effectiveness of this algorithm in a software receiver for signal acquisition and tracking and position fixing have not been fully addressed. In this paper, a narrow-band RFI mitigation algorithm based on spectrum analysis is fully discussed with respect to acquisition, tracking and position fixing. A series of hardware simulation tests are presented to assess the performance of this algorithm. For high level interference, a fixed detection threshold as previously suggested in the literature is not good enough. An adaptive detection threshold that is a function of the standard deviation of the normalized spectrum and the correlator power output is therefore proposed herein. Soft threshold in bit synchronization and improved acquisition based on earlier information are used in high dynamics and in a high interference environment. The factors that are crucial for weak signal detection, namely coherent integration time, tracking loop bandwidth and integration time in the loop filter are examined to assess the effectiveness of this algorithm. Some interference suppression strategies for spread spectrum systems, namely windowing and overlap processing, were also investigated.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	144 - 155
Cite this article:	Jiang, Z., Ma, C., Lachapelle, G., "Mitigation of Narrow-band Interference on Software Receivers Based on Spectrum Analysis," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 144-155.
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