Weak GPS Signal Acquisition Using Antenna Diversity
Date
2014-12-03
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Abstract
GNSS 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.
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Engineering--Electronics and Electrical
Citation
Mozaffari, M. (2014). Weak GPS Signal Acquisition Using Antenna Diversity (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/28677