Optimal and suboptimal coherent acquisition schemes for PN sequences with data modulation

Almost all previous acquisition schemes for direct-sequence spread-spectrum systems assume that there is no data modulation. However, in some applications, there is need for acquisition systems with the presence of data modulation, which is what we consider in this paper. First, we derive an optimal scheme using maximum likelihood estimate, by treating the phase of the incoming sequence as a signal parameter to be estimated. Two practical parallel search schemes as approximations to the optimal scheme are presented. We also consider serial and hybrid search schemes. Numerical results show that significant degradation of the standard coherent acquisition schemes occurs when there is data modulation. Using the proposed search schemes, performance is restored to the level which is almost equal to that of the standard schemes without data modulation.<>