Multi-user Detection In Mobile Communication

In the cellular mobile communication system, there are many users needing to communication simultaneously in the same district. All the users in the CDMA system occupating the same slot and the same frequency, relying solely on the selected address codes to distinguish each other, however, actually the selected address codes can not guarantee complete orthogonal, so that multiple access interference must exit in the multi-user communication system. Multi-user detection technique take full use of the known structure information and statistical characteristics of the spreading codes, also adopt certain signal processing means to eliminate interference from all other users to the expectations use, it is entirely possible to eliminate the negative impact of multiple access interference on the system in theory.The multi-user detection technique in the DS-CDMA system is firstly studied and detection model is given, then theory analysis and performance comparison on the detection algorithms of traditional linear and nonlinear are done respectively in this paper. On the second, based on the different sizes of received signal power size, a multi-user detection algorithm based on power-grouping of partial parallel soft interference cancellation is proposed , In this model , users'signal are divided into several groups according to their power size firstly, then parallel soft interference cancellation is used in the same groups and serial interference cancellation is used in different groups that is to detect users in turn, by which the complexity of parallel interference cancellation is reduced. The theory and simulation results show that the performance of the algorithm used in this paper is better than other parallel interference cancellation algorithms related in this paper and improve the system capacity. In addition, blind multi-user detection techniques is discussed in this paper and an improved PASTd subspace tracking algorithm is proposed which introduce the partial interference cancellation and Schmidt orthogonalization method so that it avoids the accumulation of computational error and algorithm divergencing, simulation results show that the improved PASTd algorithm convergence fastly and improved bit error rate performance.With the multi-user detection technique becoming increasingly sophisticated, their applications have also expanded continuously, research of multi-user detection on the MIMO system become a hot topic at present. At last, interference cancellation multi-user detection technique is studied in the MIMO system, briefly introducing MIMO communication system, giving V-BLAST signal model and systems structure, analying several multi-user detection algorithm and comparing their performance by simulation.