The performance of acousto-optic correlators (AOC) in spread-spectrum receivers is considered. The received pseudorandom sequences are correlated with reference ones in an acousto-optic cell. In particular, the effects of receiver filtering on the AOC processing gain are analyzed in the presence of additive white Gaussian noise (AWGN). The signal processing method is presented. For ideal AOCs, simple analytical expressions are derived for two different types of receiver filters: ideal and RC first-order filters. The results are given in terms of the ratio of the code rate to the filter bandwidth. They show approximate processing gain losses of 4 dB for the first type and 1 dB for the second type for =5. For real AOCs, the results are obtained from numerical simulation.
A space-integrating acousto-optic processor conceived for Global Positioning System (GPS) signal acquisition is presented. The main advantage of the proposed system, as compared with traditional ones, is that only one parameter estimation, Doppler shift, is needed, instead of two. The GPS clear and acquisition (C/A) codes are matched to a paratellurite Bragg cell in time-compression hardware with a compression factor of 20. This technique is further exploited for accelerating Doppler estimation. Experimental results show an acquisition time of at most 1 ms.
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