Weak GPS Signal Acquisition Using Antenna Diversity
SubjectEngineering--Electronics and Electrical
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AbstractGNSS Acquisition in fading and attenuated environments is challenging. In these situations, additional processing gain is required. A common method is to extend the coherent integration time. However, in weak signal situations, using only long coherent integration is limited by navigation data bit transitions and receiver oscillator instability. Using non-coherent and differentially coherent integration mitigates the bit transition problem but has lower processing gain as compared to coherent integration. Coherent, non-coherent and differentially coherent combining methods are not effective in dense multipath fading situations where the carrier-to-noise ratio (C/N0) varies significantly. Spatial antenna diversity provides additional processing gain to overcome multipath fading since multiple antennas detect signal components from independent fading channels. This thesis evaluates equal gain combining of two independent antennas in a standalone acquisition process. Traditionally acquisition has been evaluated at the cell level, which considers only a single cell, but in this thesis acquisition is assessed at the system level, where the complete acquisition process including the entire search space is examined. Receiver Operating Characteristic (ROC) curves in both cell and system levels are presented and compared both theoretically and using real data. Overall detection probability, probability of false alarm and acquisition time are investigated in terms of the mean and variance values. Optimal values for the integration time as well as combination of coherent and non-coherent integration that minimizes the mean acquisition time are obtained. The theoretical analysis is compared with Monte Carlo simulations and real GPS data results. Compared to a single antenna, smoother signal-to-noise ratio (SNR) values which show the fading mitigation were observed by applying diversity combining. Experimental results demonstrate the improvement of detection probability, enhanced immunity against false alarms, and significant reduction of the mean and variance of acquisition time in dense multipath environments.
CitationMozaffari, M. (2014). Weak GPS Signal Acquisition Using Antenna Diversity (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/28677
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