A Study On DS-CDMA Signals Blind Estimation Technique

DS-CDMA(Direct Sequence-Code Division Multiple Access)signals have been widely used for military and civil communication,satellite navigation and other fields due to their low probability of intercept,anti-jamming and code division multiple access.In non-cooperative applications,due to the unknown spread spectrum sequences of each user,the DS-CDMA signals should be estimated in a blind manner to despread the signals.Therefore,the blind estimation of DS-CDMA signals plays an important role in non-cooperative scenarios.In this thesis,we consider the problem of blind estimation of DS-CDMA signals.To solve this problem,we study the mathematical model of DS-CDMA signals under different scenarios and propose different blind estimation algorithms based on the characteristics of the various models.The main work is as follows:1.For the problem of blind estimation for synchronous and asynchronous short-code DS-CDMA signals under single channel receiving scenarios,we present a fast blind estimation algorithm based on the iterative least squares with projection algorithm.The proposed algorithm has low computational complexity compared with expectation maximization algorithm when the number of users is large.For the problem of great computational burden on conventional subspace estimation,an improved algorithm based on segment subspace estimation method is proposed.2.For the problem of blind estimation for long-code DS-CDMA signals under single channel receiving scenarios,this thesis presents a blind estimation algorithm that relies on expectation maximization and iterative least squares with projection algorithm.We also propose another two blind estimation algorithms.One is based on segment subspace estimation and the other is based on the special structure of the signals.3.For the problem of blind estimation for synchronous short-code DS-CDMA signals under multi-channel receiving scenarios,we introduce a blind estimation algorithm that relies on third-order tensor decomposition.Aiming at the problem of blind estimation for asynchronous short-code DS-CDMA signals,we propose a blind estimation algorithm based on rank F-F-1 decomposition of the tensor model.For the problem of blind estimation for synchronization long-code DS-CDMA signals,a blind estimation algorithm is proposed.The proposed algorithm build DS-CDMA signals as missing PARAFAC model,and then use the alternating least squares algorithm to implement the low-rank decomposition of the missing PARAFAC model to obtain the estimation matrix of the signal matrix.4.In this thesis,we consider the problem of blind estimation of short-code DS-CDMA signals in a multipath propagation environment with intersymbol interference.To solve this problem,we propose a blind estimation algorithm based on iterative least squares with projection algorithm.Aiming to multi-channel receiving application,this thesis presents a blind estimation algorithm that relies on rank F-F-1 decomposition of tensor model.