A closed-loop coherent PN acquisition system with a pre-loop estimator

We propose a closed-loop system with a pre-loop code phase estimator (PLE) for acquisition of the pseudonoise (PN) signal in direct-sequence spread-spectrum systems. It consists of two major parts: a PLE and a closed-loop acquisition subsystem. The system uses an auxiliary signal, as opposed to the PN signal itself, to correlate with the incoming signal. The PLE uses the correlation result to obtain an estimate of the incoming code phase. Then, starting with this initial estimate, the closed-loop subsystem will acquire the code phase of the incoming PN signal. With coherent carrier demodulation, mean and variance of the acquisition time of the proposed scheme are obtained and compared to those of the conventional serial-search acquisition receiver and the closed-loop system without the pre-loop estimator. Results show that, with proper choices of parameters, the proposed system acquires the PN phase significantly faster than the other two systems.