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Fast acquisition implementation for high sensitivity global positioning systems receivers based on joint and reduced space search

Fast acquisition implementation for high sensitivity global positioning systems receivers based on joint and reduced space search

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In Global Positioning Systems (GPS), unique pseudorandom codes allow different satellites to share available frequency spectra without interference. In receivers, the locally generated codes (replicas) are correlated with received signals to extract a particular satellite's signal and wipe-off its pseudorandom code. The signals received are generally misaligned with replicas. As a result, receivers search for signals using different codes, code phases, and additional residual sinusoidal demodulations at several possible frequencies. This search is called acquisition and it is computationally challenging for receivers operating under weak signal conditions. Software GPS receivers have been developed over the past several years and continue to be an area of extensive research. Faster, less complex, and more efficient algorithms are required for software GPS receivers. We present a fast algorithm for accelerating acquisition. Several frequency domain approaches proposed by authors earlier are combined to reduce computational complexity. These are (i) joint code, code delay and frequency search; (ii) limited code-phase search; and (iii) a shifting replica approach. Significant gains in arithmetic complexity are achieved. A novel method for restoring correlation degradation introduced by limited code phase search is also presented in this paper. Overall performance of the acquisition is illustrated on different platforms.

Inspec keywords: demodulation; Global Positioning System; random codes; synchronisation; radio receivers; communication complexity; software radio

Other keywords: computational complexity; joint code; pseudorandom codes; arithmetic complexity; satellites; residual sinusoidal demodulations; code delay; code-phase search; software Global Positioning Systems receivers; correlation degradation restoration; shifting replica approach; frequency search

Subjects: Radionavigation and direction finding; Satellite communication systems; Codes

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