Linear Filter Design For Multi-User MIMO-Relay Systems

Ubiquitous broadband wireless access is envisioned as an ultimate goal of future wireless communications systems. In conventional cellular networks, promoting the users'throughput around the edge of the cell is a challenging obstacle on the way to this destination. By the deployment of relay nodes (RNs) in traditional cells, relay enhanced cellular network structure is designed to extend the high-date-rate coverage at a low cost and complexity. Facing the future wireless communication system, the MIMO (Multiple-Input-Multiple-Output) technology can greatly improve the transmission reliability and system capacity by deploying multiple antennas on transceivers.Applying MIMO techniques relay networks, has brought new challenges for the physical layer, we need to design of the linear filter matrices on different nodes to make full use of the multiplexing gain and improve the system throughput. This paper mainly focuses on a multi-user MIMO relay system. Based on the HAF relay, linear filters on each node are analyzed theoretically and corresponding joint linear filter design for the multi-user MIMO relay system and robust linear filter design algorithm are proposed. By modeling and simulation, the feasibility and performance of proposed strategies are also validated. The sketch of this paper is outlined as follow:Firstly, this paper addresses the filter design and user selection issues for the downlink of a multi-user MIMO-relay system. To eliminate interuser interference, the filter design is based on the singular value decomposition (SVD) of the first hop link and block-diagonalization (BD) for the second hop link. Then the problem is converted to the power allocation problem at the relay station (RS). It can be determined in a closed-form by the water-filling policy. In a practical system with a large number of users, the RS need to select a subset of best users to serve. The exhaustive search for the optimal userset is, however, computationally prohibitive. Therefore, we propose a low-complexity algorithm that is based on the MIMO-relay channel capacity. Simulation results show that the proposed linear filter design scheme achieves significant system performance improvement compared with the equal power allocation scheme and the user selection scheme allows for a reasonable tradeoff between the complexity and performance.Secondly, this thesis presents a robust linear processing scheme for the downlink of MIMO-relay systems with imperfect channel state information (CSI) aiming to minimize the mean squared error (MSE). The imperfect CSI consists of the channel estimate and the estimation error covariance matrix. The robust linear processing is based on the associated Karush-Kuhn-Tucker conditions. After obtaining the solution to the optimization problem, we investigate the effects of the channel estimation errors and antenna correlation on system performance. Simulation results show that the robust linear filter design scheme is capable of alleviating the effects of CSI errors and improving the robustness of system.Thirdly, this paper also presents the evaluation of the relay performance in IMT-advanced and research on the radio resource management in relay system. The simulation results show Introducing relay into wireless networks can bring considerable throughput gain compared to without relay case. The throughput performance of the LTE-Advanced system with typeⅠrelay is limited by the intra-cell interference among the eNB and relay nodes.Finally, conclusions and future work are summarized.