Research Of Rapid PN Code Acquisition Using Iterative Message Passing Algorithm

Exact synchronization of PN code is the precondition of the excellences of spread spectrum communicating system, and how to rapidly and effectively make the PN code to exact synchronization becomes the key of the excellent performance of spread spectrum communicating system. And the rapid acquisition technology of PN code is the effective method to remove the powerful sky-wave disturb in the wireless navigation system taking earth-wave. For those reasons, this paper introduces a new rapid PN code acquisition method using iterative message passing algorithm (IMPA).Firstly, this paper analyses two kinds of common PN code acquisition technology which are simple serial acquisition and hybrid acquisition. Simple serial acquisition searches every phase and decides whether the phase of local pseudo code is synchronization with the coming using the correlation. Evidently, hardware expenses of simple serial acquisition are smaller than other method, but the average acquisition time is longer. The simple serial acquisition can work under lower signal-to-noise ratio environment because the method implements sliding searching for to every phase of pseudo code. Comparing to the simple acquisition, the hybrid acquisition method is rapider and its hardware equipment is more complexes. This paper presents the changing curves of detection probability and false-alarm probability and average acquisition time with the unitary threshold and signal-to-noise ratio. Then, the algorithmic principle of IMPA has been introduced in details, which include factor graph theory, message passing algorithm based on the factor graph theory, and the basis for understanding IMPA is established profoundly.This paper gives the principle of the rapid PN code acquisition method using IMPA and a flow chart of realization of it, and realizes the key of the new acquisition algorithm and a simulation's spread spectrum system using C language and carries out the emluator then gets the main performance parameter. In some aspect, the rapid PN code acquisition technology using IMPA has advantage over the hybrid acquisition method, which is proved by the computer simulation.