Research On Precoding Scheme For MIMO Relay Systems With Imperfect Channel State Information

Multi-input multi-output(MIMO)relay system combined the advantages of MIMO technology and relay technology,which can significantly improve the system coverage and spectrum utilization.As a key technology that can further improve the performance of MIMO relay systems,it has been aroused the attention of academia.The precoding design needs to obtain the channel state information.However,due to the limitation of the channel estimation method and the existence of channel feedback delay,the ideal CSI is difficult to obtain.In this paper,the linear precoding design schemes based on imperfect channel state information(CSI)are proposed for the MIMO system,the single-user MIMO relay system,the multi-user MIMO relay system and the MIMO two-way relay system in order to improve the system bit error rate.The main research works are as follows:(1)For MIMO system,a linear precoding scheme design is investigated based on minimum mean square error(MMSE)criterion with the channel estimation error and feedback delay.The Lagrangian multiplier method,the partial derivative method are introduced for solving the unconstrained optimization method and the constrained optimization problem,respectively.Finally,an alternating algorithm is proposed for the joint design.Those researches laid the foundation for the precoding algorithm of MIMO relay system in the following chapters.(2)A precoding algorithm is proposed for single-user MIMO relay system based on MMSE criterion with the channel estimation error and feedback delay.The maximum power constraint at the transmitter and the relay node are taken into account.By introducing the correction factor with Lagrange multiplier method and KKT criterion,the optimization problem of solving the three-node matrix is transformed into a system of multiple equations with inequality constraints.Finally,the joint iterative method is used to update each node matrix optimally solution.Simulation results show that the proposed algorithm significantly improve the BER performance of single-user MIMO relay system compared with the exist approaches.(3)A precoding scheme based on MMSE criterion is proposed for the uplink multi-user relay system with the channel estimation error and feedback delay.The proposed precoding algorithm decomposes the constrained optimization problem into three sub-convex optimization problems and solve separately.The transmitter that equipped with single antenna is subject to independent distribution,it can be assumed that the precoding matrix is a diagonal matrix.The convexoptimization problem of relay matrix is transformed into semi-definite programming problem(SDP),which can be solved by toolbox.The equalizer matrix can be introduced by the gradient-based line search algorithms.Then the optimal solution is obtained by using iterative iteration.The simulation results show that the proposed scheme can achieve better system performance than the sub-optimal scheme without relay precoding.(4)For MIMO Two-way relay system with the channel estimation error and feedback delay,two precoding algorithms are proposed based on MMSE,which are matrix decomposition method and joint iterative method.The matrix decomposition method transforms the matrix optimization problem into the scalar element optimization problem in the matrix and solve it by dichotomy method.The joint iterative method alternately updates the matrix until the algorithm converges,then the optimal relay precoding matrix and the optimal equalizer matrix is obtained.Simulation results shows that the proposed design approach achieves better BER performance than other approaches.