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Multiwavelet Analysis And Its Applications In CDMA

Posted on:2002-12-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:J PanFull Text:PDF
GTID:1118360062475194Subject:Circuits and Systems
Abstract/Summary:PDF Full Text Request
Multiwavelet analysis and its applications in CDMA systems are investigated in detail in this dissertation. The main work can be summarized as follows.1. A method for determining the associated multiwavelets from a class of multi-scaling functions using the genetic algorithm is proposed. It is important to determine the associated multiwavelet generated by a multi-scaling function for the flexible application of the multiwavelet analysis, and this can be converted equivalently into a problem of optimization in a high dimensional space under some conditions. The genetic algorithm, which simulates the evolutional process of the nature, is a global and robust algorithm, and the construction of orthogonal multiwavelets via genetic algorithm makes the guideline to determine multiwavelets clear and simple.2. A method for determining the associated multiwavelets from a class of multi-scaling functions using eigenvalues and eigenvectors of matrices is proposed. The theoretical analysis shows that under some conditions the associated wavelet sequence of a multiwavelet system can be constructed by eigenvalues and eigenvectors consisting of the scaling sequence of the multiwavelet system. This construction method is not restricted by the multiplicity of multiwavelets.3. The concept and the model of the multiwavelet neural network is proposed. Its universal and L: approximation properties as well as its consistency are proved, and the convergence rates associated with these properties are given. The theoretical analyses show-that multiwavelet networks can have more rapid convergence rate than wavelets, but wavelet networks can have better choice of initial values. To make a comparison between both networks experiments are carried out with GHM multiwavelet network and Daubechies 2 wavelet network.4. A method for the preprocessing of multiwavelet neural networks is presented. Initialization is a crucial problem in the application of multiwavelets, and the selection of initial weight affects directly the approximation performance and convergence rate of a multiwavelet neural network. The preprocessing method presented here gives a better scheme for the selection of initial weights of multiwavelet neural networks.5. The multiuser detection based on multiwavelet neural networks is proposed. Themultiwavelet neural network is characterized by high approximation performance and rapid convergence, and so the multiuser detector based on a multiwavelet neural network possesses its advantages over existing neural network-based multiuser detectors. Moreover, the dimension-reducing preprocessing presented in the thesis improves the performance of the multiwavelet neural network detector.6. Based on the method of subspace, the problems of the estimation of active users and timing in asynchronous CDMA systems are studied, the algorithms of the estimation of active user and timing are given, and the performances are analyzed. Furthermore, the problems of the estimation of channel parameters and timing are discussed in multipath fading asynchronous CDMA communication system. Combing the method of subspace with output energy minimum criterion, we give the estimated values of the channel parameters and timing of the desired user, and many computer simulations show the efficiency of the proposed methods in the case of different SNR and different SIR.7. A multiwavelet-based code-division multiple-access (MW-CDMA) scheme is presented based on the application of recent results in multiwavelet analysis filter, preprocessing and balancing to communications area. In MW-CDMA. at first, the received signal is decomposed into the components in the orthogonal wavelet spaces, and then the multiuser demodulation is implemented in each wavelet space. Theoretical analyses and experimental results show that MW-CDMA systems suppress multiple-access interference and ambient noise well. Moreover, the scheme gives a new guideline of thought to reduce the computation for demodulating.8. Multi...
Keywords/Search Tags:Multiwavelet, Multiwavelet with short sequence, Genetic algorithm, Multiwavelet neural network, Preprocessing, Balance, CDMA, Multiuser detection, Estimation of timing, Multiwavelet CDMA, Mlutiwavelet analysis filter, Haar lowpass filter
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