Interference Cancellation Using Power Minimization and Self-Coherence Properties of GPS Signals (Preprint)
AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH SENSORS DIRECTORATE
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This paper presents the performance analysis of two digital beam forming techniques used in conjunction with a software GPS receiver to mitigate interference to GPS signals in jamming environment. The first method is the constrained minimum power MOP method. The second method is the so-called self-coherence restoral SCORE method. Both experimental and simulation data are used in the study. The study was performed using experiment data collected in an anechoic chamber to obtain GPS and interference signals. A two by two GPS antenna array and a four channel radio frequency front end are used to collect simulated GPS data generated using hardware-based simulator in controlled jamming environment. Three types of interference signals are deployed in the experiments FM chirp, binary phase shift key, and broadband. The interference power levels used were 20, 30, and 40 dB above GPS signal power. A software GPS receiver was used to perform acquisition of GPS signals to evaluate the performance of the beam forming algorithms. The preliminary result showed that MOP method can effectively mitigate all three types of interference at all power levels if a single jammer is present. Experiments using multiple broadband jammers were also analyzed and our results shown that the effectiveness of the MOP diminishes as the jammer power increases and ceases to function at the 40 dB level. The SCORE method does not exhibit consistent performance for the experimental data. This is consistent with our simulation results which show that for the SCORE algorithm to generate satisfactory results, sufficient number of antenna elements is necessary even if there is no interference source present. The number of antenna element is determined by the number of satellites available, as well as the number of interference source.
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