Research On Multi-user Detection And PAR Reduction Technologies For Modern Mobile Communication Systems

Code Division Multiple Access (CDMA) becomes main stream in 3rd generation mobile communication systems due to its attractive features, such as anti-jamming, low intercept probability. But, the CDMA system is an interference constrained system and Multi-Access Interference (MAI) due to many simultaneous users constitutes the main limitation of DS-CDMA systems. Any interference cancellation technology will increase the capacity of the system, and Multi-User Detection(MUD) is for one. This dissertation focuses on the blind MUD and semi-blind MUD techniques.Orthogonal Frequency Division Multiplexing (OFDM) is one of the key techniques of the next generation high rate communications system due to its attractive features, such as high spectrum efficiency, multi-path fading mitigation. A main disadvantage of OFDM is potentially high PAR values. The use of the non-linear apparatuses such as amplifiers,A/D converter and D/A converter will cause inefficiency, interference and performance degradation. So, this dissertation also focuses on the PAR reduction techniques.The semi-blind multi-user detection has been considered for CDMA system where the codes of some users are known while others are unknown and the non-blind MUD and the blind MUD can't suppress MAI efficiently. A joint MUD algorithm of decorrelating algorithm and Non-Standard Linearly Constrained Constant Modulus(NSLCCM) algorithm which called semi-blind CM algorithm is proposed and another joint algorithm of decorrelating algorithm and Least Square CM(LSCM) algorithm is also developed in this paper. The performance of the algorithms is compared to that of the purely blind algorithm and non-blind algorithm, and the semi-blind algorithms are seen to have excellent SIR performance and BER performance.Based on the LSCM algorithm and subspace approach, a joint blind algorithm called LSCM-SUB algorithm is developed. The proposed LSCM_SUB algorithm can achieve fast convergence performance and better SIR and BER performance than theLSCM algorithm especially in the low SNR.And then, the LSCM-SUB algorithm is applied in the semi-blind MUD and results in the semi-blind LSCM-SUB algorithm. The proposed algorithm has superior convergence and stabilization performance and it is more robust in the case when the system is heavily loaded.As for the high peak to average ratio of the OFDM system, a joint approach of interleaving and phase rotation method called IPR is developed and a novel phase rotation vector form is proposed. A few of interleavers are used in the transmitter in the IPR approach. To de-interleaving, the receiver must know the interleaving order in the transmitter. So, the Side Information (SI) is used to implement it and the system overhead is increased because of it. To avoid introducing the SI, a blind detection approach in the receiver whose idea is from the Rate Decision (RD) approach in CDMA systems is proposed. The de-interleaver number is determined through the CRC decision vector and the reverse SER vector. The approach can achieve significant detection performance.The application of the IPR approach is evaluated in the IEEE 802.16d system. Compared with the performance of the IEEE 802.16d standard, the IPR method achieves better Complementary Cumulative Distribution Function (CCDF) performance without BER performance degradation almost.