Multi-Carrier Spread Spectrum Communication And Its Multi-User Detection Technology Research

Multiple access system based on CDMA have been greatly favored in mobile communication applications.However,the performance of CDMA system is limited by both multiple access interference and inter-symobol interference(ISI).At the same time,OFDM technology has been more and more mature while its performance on resisting multipath fading is outstanding.Multi Carrier-Code Division Multiple Access(MC-CDMA)is a new Multi-carrier modulating technology for broadband mobile wireless communication.It combines the advantage of OFDM and CDMA,it can convert the frequency selective attenuation channel of the broadband to flat channel of the subcarrier.It has adaptive flexibility,high capacity,high bandwidth efficiency and interference robustness.It can be used for high speed data transmission,has attracted much attention in recent years.So it is considered as the core technique of the future 4G wireless communication system.In this paper, the development of MC-CDMA and related technology are first introduced, and the basic principle of CDMA,0FDM and OFDM-CDMA are illuminated.Based on the analyzing and comparing of three solutions of OFDM-CDMA,it can be conclued that MC-CDMA is superior to others in performace.Then the predigested MC-CDMA system model is established and its simulation flow chart in Matlab is proposed,include the model of transmitter,wireless channel and receiver,and then its key techniques are analyzed.Some technologies of MC-CDMA and their functions in MC-CDMA system are emphasized,such as frequency spread of data in frequcency domain,IFFT/FFT and Cyclic Prefix,and so on.And then,several commonly used linear and nonlinear suboptimal multiuser detectors are described,and their advantages and disadvantages are pointed out respectively.Lastly,the simulation results of these suboptimal detectors are given.At last,the discrete wavelet transform and wavelet MultiResolution Analysis(MRA) algorithm are introduced briefly.Then,an improved wavelet MRA algorithm proposed is illustrated in detail,and the corresponding decomposing and reconstruction formula are proposed and demonstarted.In the second part of this chapter,the discrete wavelet transform is incorporated into the multiser detection for asynchronous DS-CDMA systems,and form the Wavelet Transform based Multiuser Detector(WTMUD).Lastly,the principles and implementation of Genetic Algorithm(GA) are introduced,then the GA is used to optimize the outputs of WTMUD,and so form the hybrid Wavelet Transform and GA based Multiuser Detector(WTGAMUD).