Ds And Ds / Cdma Signal Blind Detection And Estimation Methods

Direct sequence spread spectrum (DS) signals have been widely used for military communication and mobile communication known as Code Division Multiple Access (CDMA) system. Because DS signals have many advantages such as anti-jamming capability, low probability of interception, multiple access capability,and so on. Accordingly, the interception and anti-jamming technology for spread spectrum communication have been of great research interests. And the chief task is to detect and estimate the DS/CDMA signals.A class of DS/CDMA signals estimation methods has been developed. The methods are almost based upon the theory of conventional signal detection and estimation.However the DS/CDMA signals are wide-band weak signals, they aren't in conformity with the theory of conventional signal processing, so when the signal to noise ratios of the received signals becomes lower, the performance of the methods take a turn for the worse, the methods don't work. Presently, the development of DS/CDMA signal estimation is very slow, it is almost in study of conception and the study of concrete method is far from comprehensive and mature.The main contributions of this dissertation include two aspects. One is parameter estimation of the DS/CDMA signal, include period estimation and chip interval estimation of the PN sequence etc., the other is PN sequence estimation of the DS/CDMA signals. At first, to estimating common parameters, in this dissertation three detection methods-square detection, pre-processed revised cycle-spectrum algorithm and power spectrum reprocessing approach are applied to detect the DS/CDMA signal. These three methods have different advantages and disadvantages respectively. Every method can estimate a different parameter of the signal with good performance. The square detection can picks up the carrier frequencies, which is simple and has great performance. But this method can't recognize the signal as spread spectrum signal. The pre-processed revised cycle-spectrum algorithm can estimates the chip rate of signal's PN sequence. The shortcoming of pre-processed revised cycle-spectrum algorithm is its complexity and in need of long time to compute. A simple and powerful approach is power spectrum reprocessing approach , which can estimate PN sequence's time period. Using this parameter and the PN chip rate estimated by spectral correlation method, we can get another parameter, length of the PN sequence. In order to solve the estimation problem of PN sequence itself, we presented a matrix eigenvalue decomposition approach to estimate the PN sequence itself. Through decomposition of the correlation matrix of DS/CDMA signals, we can estimate the PN sequence from the largest and the second largest eigenvector. An effective synchronization of the PN sequence can be achieved by maximizing the squared Frobenius norm of a covariance matrix is of central importance in our approach.