Applying Fast Fourier Transform Analysis and Data Window in Software Global Positioning System Receivers to Mitigate Continuous Wave Interference under Dynamic Conditions

Abstract

Traditionally, most Radio Frequency Interference mitigation methods have been 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 together with modern digital signal-processing techniques. This paper describes an investigation into the development of a narrow-band Continuous Wave (CW) interference mitigation algorithm and performance testing using a software Global Positioning System receiver based on Fast Fourier Transform analysis and data windowing. In this paper, some strategies were proposed to improve the anti-jamming performance. First, for high-level interference, a fixed detection threshold suggested in previous literature is not optimal. An adaptive detection threshold that is of better performance and is a function of the standard deviation of the normalized spectrum and the correlator power output was used in lieu. Second, a priori information-based soft thresholding techniques for both bit synchronization and enhanced signal acquisition were applied under high dynamic conditions and high-level interference environments. The factors that are crucial for weak-signal detection and tracking, namely, coherent integration time, tracking loop bandwidth, and integration time in the loop filter were evaluated to assess the effectiveness of this algorithm. Some interference suppression strategies for spread spectrum systems, namely, windowing and overlap processing, were also investigated. Test results proved that the proposed algorithm is effective to mitigate narrow-band CW interference under certain power level. Windowing and overlapped processing are good strategies to further improve the anti-interfernce capability by 2 dB.