Rapid acquisition for long PN code under low SNR

A rapid acquisition based on iterative message passing algorithm (iMPA) was developed to solve the problem of rapid acquisition for a long pseudorandom (PN) code under low SNR. Tanners' factor graph was used to represent the m sequence via demonstrating that m sequence is a sort of especial linear block code, and then the message passing algorithm was executed iteratively to estimate the original phase of the received m sequence over the graph model. Both analysis and simulation results show that the rapid acquisition using iMPA can work steadily under low SNR, and its detection performance drops about 5 dB comparing with hybrid acquisition. But the average acquisition time is about one tenth of the hybrid acquisition in the same acquisition environment, and the computing complexity is only one over tens of the traditional acquisition.