Multi-user Mimo Downlink Link Precoding And User Scheduling Techniques

Multiple-Input Multiple-Output (MIMO) technology can improve communication system's capacity and reliability without any more system band required. It is considered as one of the key technologies in future mobile communication systems.In recent years Multi-user MIMO systems with one base station and many users have attracted the research attention, since no extra time slots and frequency resources are needed to support more users. For the downlink,since the mobiles are decentralized, the users are not able to coordinate with each other and can not separate the signals using array processing, multi-user detection(MUD) or other methods. In this dissertation, precoding and user scheduler algorithm for multi-user MIMO downlink systems is studied. Precoding algorithms for multi-user MIMO systems, which uses the channel state information (CSI) to process the transmit signal, have to be used to pre-eliminate the spatial interference among different users. Then reduce the complexity and cost of the receivers. System capacity can be enhanced through the user scheduling. To summarize, the research includes the following aspects:The background for this research and the main content are introduced in the first chapter.Chapter 2 introduces the fundamental theory of wireless communication and basic knowledge of MIMO system including the analysis of system model performance evaluation of single user and multi-user systems are analyzed separately.Multi-user precoding and user scheduler algorithm are studied in chapter 3 under the assumption of base station has the ideal channel state information. Three kinds of precoding algorithm: Block diagonalization (BD), joint precoding and Single to Leakage and Noise Ratio (SLNR) are analyzed in detail. A novel solution for Single to Leakage and Noise Ratio precoding is presented. The performance of this novel algorithm is improved through the power allocation. User scheduling also are discussed in the scenario of BD. Optimal and suboptimal of user selection algorithm is analyzed. Simulation results show that suboptimal can reduce the complexity with few sacrifice of performance. Chapter 4 presents a novel algorithm for the construction of codebook method in multi-user systems. The novel algorithm is based on Grassmanian space. Code distance factor is considered to improve the performance of system. Then, considering the problem of low matching in unitary precoding, correlation coefficient is introduced in this novel algorithm, matching is improved through approximate SNR.Finally, the whole thesis is summarized and future research direction is pointed.