Study of interference effects on GPS signal acquisition
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AbstractInterference and jamming is one of the major concerns in using the Global Positioning System (GPS) for critical applications. The GPS system has advantages over the narrow-band navigation systems since GPS signals are spread-spectrum signals and receiver design techniques can eliminate most of the interference signals. Any signal or its harmonics near the GPS L1 and L2 frequencies are a potential source of interference. The interference signals outside GPS frequency band can be filtered out either by a GPS antenna or a receiver front-end. Interference signals within the GPS frequency bandwidth are difficult to isolate using the filters. These signals need to be mitigated either by the acquisition process or the tracking process. This thesis investigates possible interference mitigation by the acquisition process. Acquisition methods were implemented as a part of the correlator in a software receiver and used for analysis. Interference resulting from sampling in the receiver front-end and cross-correlation between the GPS Gold codes were studied. Aliasing effect introduces a loss of 2-3 dB in the acquisition gain and causes false locks for smaller sampling frequencies at a wider precorrelation bandwidth. The cross-correlation between the GPS Gold codes causes problems for the signal acquisition below -135 dBm. Different radio frequency (RF) interference signals were studied to analyze their effect on the acquisition process. Adaptive predetection integration (up to 100 ms) was performed to determine the possible tolerance to the RF interference signals. A continuous wave (CW) interference hinders the acquisition more compared to any other RF signals such as swept CW, amplitude modulated (AM), frequency modulated (FM) or broadband noise. An RF signal level of 15-25 dB above the GPS signal level was found sufficient to jam the acquisition process.
Bibliography: p. 193-204