Design of code acquisition of pseudonoise signals

There has been a growing interest regarding the study of direct-sequence spread spectrum (DS-SS) techniques for wireless mobile communication applications, the so called code division multiple access (CDMA) system, which has been shown to have significant advantages over time division multiple access (TDMA) systems. However, like other spread spectrum applications, the advantages of the CDMA system can be exploited only in the case where the pseudonoise signals of the local generator and the received signal are synchronized within a small fraction of one PN chip. In general, the code synchronization process in spread spectrum systems consists of two steps, code acquisition and code tracking. We propose a new acquisition method that uses the advantages of maximum likelihood and sequential search acquisition systems by using one characteristic of the PN code. The PN code, can be transformed to the Walsh code, that have the orthogonal property of m-sequences was exploited by Cohn and Lempel (1977) based on matrix factorisation. It can be shown that the copy feature is generally true for all PN codes, and based on this property of PN codes a new acquisition method of PN signals is proposed. In this new method, the received PN signals are first replaced in the N chip, then a copy analysis is performed followed by an estimation of the initial phase of the incoming PN code. The performance of this new method is analysed and investigated by the numerical simulations. The simulation results show that the performance of this method is the same as the maximum likelihood correlation methods.