Research On Technologies Of The Multi-user Detection In DS-CDMA/TD-SCDMA System

CDMA is a main multi-access technology in the third generation wireless communications systems (3G). The following topics are discussed in this dissertation: the structure of multi-user detection; the algorithm and performance analysis of multi-user detection for DS-CDMA and TD-SCDMA systems; the multi-user detection of TD-SCDMA system in the high-speed railway environments. All these topics play a significant role in the development of Chinese 3G wireless communications system TD-SCDMA. The main researches include the following points:1. We have proposed the multi-user detection algorithm based on the rule of least mean kurtosis (LMK) for DS-CDMA system. Then, the convergence characteristic of this algorithm is studied analytically. We have proved that the conditional LMK algorithm is global convergence under the assumption that noise is not present. Also, we have drawn that the LMK algorithm is the best solution at the global convergence point. The simulation results indicate that the performance of the proposed algorithm is close to that of the SVD sub-space multi-user detection. Moreover, this algorithm can trace the channel dynamically. The complexity of this algorithm is relatively low, thus it has some study and practical value.2. We have studied the structure of multi-user detector based on the constant modulus algorithm (CMA) in AWGN channel for DS-CDMA system. We have optimized the cost function of CMA algorithm and proposed a blinded multi-user detection algorithm, ie. sign error CMA (SE-CMA). Furthermore, we have analyzed and evaluated the algorithm in AWGN channel and multi-path channel through simulation. The results have shown that SE-CMA blinded algorithm is excellent, stable and simple. In practice, the computational complexity of this algorithm is low and easy to realize.3. We have studied the continuous and discrete transmission models for TD-SCDMA system. The minimum mean square error (MMSE) algorithm and Zero force (ZF) algorithm are applied to the multi-user detection of TD-SCDMA system. Then, we have compared the performance of normal single-user receiver with the multi-user receiver. In the last, we have proposed the multi-cell joint detection algorithm. The simulation results show that multi-cell joint detection can efficiently reduce the effect of high interference from adjacent cell. 4. Multi-cell channel estimation is proposed based on parallel interference cancellation (PIC) and successive interference cancellation (SIC) for TD-SCDMA system. The simulation results show that multi-cell channel estimation based on PIC and SIC can significantly improve the system performance. Finally, the performance of the system with multi-cell joint detection combined with multi-cell channel estimation is studied through simulation.5. With the prevail trend of mobile communications in the high-speed railway in our country, firstly, we have studied the characteristic of radio channel with high-speed. In order to reduce the effect of doppler frequency shift, we have proposed the methods of frequency offset estimation and frequency offset correction. The results have shown that these methods can highly improve the performance of TD-SCDMA system in the circumstances of high-speed railway mobility.