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 sequ ence (DS) spread-spectrum signal utilizing a purely parallel search st rategy. A parallel search strategy is utilized because it reduces the acquisition time compared to either serial or partially parallel strat egies. In particular, the purpose of this paper is to derive the optim al decision rule, based on the maximum-likelihood criterion, for frequ ency-selective fading channels. The performance of the conventional de cision rule, optimized for additive white Gaussian noise and flat-fadi ng channels, the optimal decision rule, derived in this paper, and a s uboptimal decision rule, also presented in this paper, are compared, I t is shown that the optimal and suboptimal decision rules for Rayleigh -fading channels outperform the conventional decision rule. For Rician -fading channels, it is shown both that the optimal decision rule outp erforms the conventional decision rule, and that the optimum decision rule for Rayleigh-fading channels, when implemented on a Rician-fading channel, yields approximately optimum performance.