.ds / Cdma Signal Blind Despreading Technology Research

Direct-Sequence Spread-Spectrum (DSSS) has low probability of intercept, Multiple Access, anti-jamming capability and other advantages. It has widely been used in military and civil communications. In the non-cooperative scenario, it is difficult to intercept and analysis DSSS signals with unknown spreading code sequence and other parameters.In order to achieve the Direct Sequence-Code Division Multiple Access (DS/CDMA) signal acquisition and blind dispreading, a variety of signal detection, parameter estimation and blind despreading algorithm has been analyzed, and an improved non-cooperative DS/CDMA signal receiver system has been designed. The main contributions of this dissertation are as follows.1.Complete study is made for the DS/CDMA signal intercept and blind dispreading, and a set of non-cooperative DS/CDMA signal receiver system design scheme has been proposed. In the non-cooperative scenario, the module of pseudo-code cycle synchronization has been introduced and a new carrier frequency estimation structure has been designed.2. Some DS/CDMA signal detection and feature extraction algorithms were analyzed, and some solutions were proposed to solve the possible problems in practical application.3. By studying the DS/CDMA signal model, the existing criterion for the classical fixed-order was extended to estimate the number of users in DS/CDMA system. A detailed analysis of the criteria performance and deficiencies has been made, and a new modified Akaike Information Criterion (AIC) has been discussed, the flexible performance of this criterion ensured the probability of correct estimate in case of low SNR.4. Estimation of the short-code DS/CDMA signals is also investigated in the interception and analysis context. An expectation maximization (EM)-based blind despreading approach is presented for the asynchronous DS/CDMA systems. At the same time, the hidden Markov model has been used to analyse the asynchronous DS/CDMA signal, and Baum-Welch algorithm has been used to blind despreading.