Optimal decision strategies for acquisition of spread spectrum signals in frequency selective fading channels

The focus of this paper is on the initial acquisition of a direct sequence spread spectrum signal utilizing a purely parallel search strategy. A purely parallel search strategy is utilized because it reduces the acquisition time compared to either serial or partially parallel strategies. In particular, the purpose of this paper is to derive the optimal decision rule, based on the maximum-likelihood criterion, for coarse acquisition of direct sequence waveforms transmitted over frequency selective fading channels. The performance of the conventional decision rule, optimized for additive white Gaussian noise and flat fading channels, and the optimal decision rule, derived in this paper, are compared. It is shown that the performance improvement increases as the number of resolvable paths increases. Furthermore, it is shown that the optimal decision rule for Rayleigh fading channels, and a decision rule which yields approximately optimal performance for Rician fading channels, are easily implemented.