Study On Approaches Of DS&DS/CDMA Signal Estimation

The problem of estimating direct sequence spread spectrum (DS) signals and direct sequence code division multiple access (DS/CDMA) signals direct from the received signals has been of great research interest with the development of the field of wide-band weak signal processing and the field of communication antagonism. For the last several decades, a class of DS&DS/CDMA signal estimation methods has been developed. The methods are almost based upon the theory of conventional signal detection and estimation. However the DS&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. Though DS&DS/CDMA signals are widely used in military and civil, until recently study on the DS&DS/CDMA signal estimation appeared in the literature. Presently, the development of DS&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. Due to the challenge of DS&DS/CDMA signal estimation without knowledge of the pseudo-noise (PN) sequence, the study of DS&DS/CDMA signal estimation is necessary, so that we can obtain efficient method of DS&DS/CDMA signal estimation.The main contributions of this dissertation include two aspects. One is parameter estimation of the DS&DS/CDMA signal, include period estimation and chip interval estimation of the PN sequence etc., the other is PN sequence estimation of the DS&DS/CDMA signals.Several valuable and important results which bring forth new ideas are achieved and listed as follows:1, Based upon the study of models of the DS&DS/CDMA signals, we obtain the parameters of base-band DS&DS/CDMA signals for estimation are as follows: the period and the chip interval of PN sequence, the moment of de-synchronization between observation window and symbols. Besides, we obtain waveform for estimation: the PN sequence itself.2, Based upon the study of the power spectrum of DS&DS/CDMA signals, a power spectrum reprocessing approach is presented to estimate the period of PN sequence.3, Based upon the study of the cyclic spectrum of DS&DS/CDMA signals, a spectral correlation approach is presented to estimate the chip interval of PN sequence.After synthesizing the DS&DS/CDMA signal estimation methods of time-domain correlation, we obtain two approaches. When the correlation time-delay can compare to the period of PN sequence, a time-domain correlation approach is presented to estimate the period of DS&DS/CDMA signals. When the correlation time-delay can compare to the chip interval of PN sequence, another time-domain4, correlation approach is presented to estimate the chip interval of DS&DS/CDMA signals.5, In order to solve the estimation problem of PN sequence itself, we presented a matrix decomposition approach to estimate the PN sequence itself. Through decomposition of the correlation matrix of DS&DS/CDMA signal, we can estimate the PN sequence from the largest and the second largest left singular vector.6, In order to solve the estimation problem of PN sequence itself, based upon the idea of the correlation matrix decomposition, we present the neural networks (N.N.) approach to estimate the PN sequence itself. Here, the N.N. approaches include: the principal component analysis and the principal components analysis N.N. . When the moment of the de-synchronization is known, we can use the principal component analysis N.N. to extract the first principal component of the DS&DS/CDMA signal, we can estimate the PN sequence from the first principal component. When the moment of the de-synchronization is unknown, we can use the principal components analysis N.N. to extract the first and the second principal components of the DS&DS/CDMA signals, we can estimate the PN sequence itself from them too. Compare with the existed DS&DS/CDMA signal estimation methods, an advant...