Code acquisition schemes using antenna arrays for DS-SS systems and their performance in spatially correlated fading channels

We propose parallel and serial code-acquisition schemes using antenna arrays for initial acquisition of direct-sequence spread-spectrum signals, which can lower substantially the range of detectable signal-to-noise ratio (SNR) as compared to the corresponding conventional schemes with a single antenna. The proposed schemes use the sum of all the single-antenna decision samples from antenna arrays, corresponding to an identical subsequence of a given pseudonoise code as a decision variable in order to enhance SNR of the resulting signal. We analyze the mean acquisition time performance under an additive white Gaussian noise channel and spatially correlated time-varying flat Rayleigh fading channels by deriving the expressions for the probabilities of detection, missing, and false alarm. We consider two extreme cases of spatial fading correlation among antenna arrays, the case of uncorrelated diversity antennas and the case of perfectly correlated antennas. From numerical results, we see that the acquisition performance of the proposed schemes using antenna arrays becomes improved continually as the number of antennas increases and the performance improvement depends on the degree of spatial fading correlation.