Multiuser Detection For DS-CDMA And MC-CDMA Systems

It is evident that the 3rd Generation (3G) and beyond 3G (B3G) mobile communication will greatly facilitate and enrich our work and daily life, with the rapid development of modern digital mobile communication techniques. In order to provide colorful multimedia service and high rate data service, the 3G and B3G communication systems need higher wireless capacity. The traditional resources that have been used to add capacity are radio bandwidth and transmitter power. However, these two resources are among the most severely limited in the deployment of modern wireless networks. Therefore, people have started to investigate novel signal transmission techniques and advanced receiver signal processing methods to increase wireless capacity without attendant increase in bandwidth or power requirements, and multiuser detection technique is one of the most important research domains.Direct Sequence Code Division Multiple Access (DS-CDMA) technique is an important part of the CDMA standards, and it is the key to implement the wireless multimedia communications. But DS-CDMA is not suitable to the very high transmission rate. Therefore, DS-CDMA is combined with Orthogonal Frequency Division Multiplexing (OFDM) to form the MultiCarrier CDMA (MC-CDMA), which can support high rate transmission. MC-CDMA is the acknowledged most promising scheme for future wideband wireless communications.This dissertation mainly focuses on the multiuser detection in DS-CDMA and MC-CDMA systems. In Chapter 2, the necessity of introducing multiuser detection in CDMA systems is expounded, and the principles of multiuser detection and the optimal multiuser detector are presented. 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.In Chapter 3, the discrete wavelet transform and wavelet MultiResolution Analysis (MRA) algorithm are introduced briefly. Then, an improved wavelet MRA algorithm proposed by the author is illustrated in detail, and the corresponding decomposing and reconstruction formula are proposed and demonstrated. Using the improved wavelet MRA algorithm and conjugate quadrature filters, the author proposes a novel wavelet comb filter, which has the same resolution in all frequency bands and can detect the frequency components on the cross points of neighboring subbands. In the second part of this chapter, the discrete wavelet transform is incorporated into the muitiser 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).In Chapter 4, the encoder and decoder of Turbo code, and Maximum Aposteriori Probability (MAP) decoding algorithm are described compactly. And the iterative processing techniques based on Turbo principles and their applications are discussed. Areduced Turbo multiuser detection scheme based on Minimum Mean Square Error (MMSE) criterion is proposed, with is suitable for Turbo coded DS-CDMA systems in flat Rayleigh fading channels.In Chapter 5, the subspace based decorreiating detector, MMSE detector, and inter-symbol decorreiating detector are discussed in asynchronous MC-CDMA systems. An improve projection approximation subspace tracking algorithm is derived, and its tracking ability is analyzed. The performance simulation results of subspace based decorreiating detector, MMSE detector, and inter-symbol decorreiating detector implemented by blind adaptive algorithms are given. At last, a minimum bit error rate detector for asynchronous MC-CDMA systems, and its performance simulation are given.