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

Multi-input multi-output(MIMO)relay technology has gained extensive attention due to its wide coverage,high rate of transmission rate and resistance to channel fading effectively,improve the cell edge user service quality advantages widely followed.As a kind of adaptive technology which can improve the performance of system,precoding technology has become a research hotspot.In the case of remote transmission distance,take the direct path of the transmitter and receiver into account.In addition,due to the limitation of channel estimation technology and the short distance between antennas,the channel estimation error and antenna correlation are considered when the MIMO relay system is designed.Therefore,this paper focuses on several common MIMO relay systems with direct link,and studies the precoding algorithm in the non-ideal channel condition with channel estimation error and antenna correlation.The main research works are as follows:1.For MIMO relay system with direct link,a joint optimized algorithm is proposed based on the Minimum Mean-Squared Error criterion and constrained by maximum power at transmitting and relay terminal,which take antenna correlation and channel estimation error into account.First of all,the receiver is known as Wiener filter.Through transforming constrained problem into two sub-convex optimization problems with respect to object variables,the precoding matrix can be obtained by using projected gradient method and CVX toolbox.Finally,an alternating algorithm is proposed for the joint design.Simulation results indicated that the proposed design scheme can achieve better performance.2.On the research of the MIMO relay system of the previous chapter,for multi-user MIMO relay system with direct link,a precoding algorithm is proposed which is constrained by maximum power at transmitting and relay terminal and considered channel estimation error and antenna correlation.Due to the transmitter is equipped with a single antenna and is subject to independent distribution,it can be assumed that the transmitter precoding matrix is a diagonal matrix.Using the Lagrange multiplier method and the rule of KKT to transform the constraint optimization problem,and the bisection method can be applied to solve it to obtain the relay precoding matrix.The receiver can be expressed as the Wiener filter.Finally,the optimal solution is obtained for the joint iteration of each matrix.The simulation results verify the effectiveness of the proposed algorithm.3.For MIMO multi-relay system with direct link,take the channel correlation and channel estimation error of each node antenna into consideration,a precoding algorithm based on MMSE criterion is proposed.By substituting the expression of the receiver into constrained optimization function,the problem can be transformed into two sub-convex optimization problems.The solving problem of the terminal precoding matrix can be converted into SDP semi-positive programming problem and solved by the interior point method.The terminal precoding matrix is solved by Lagrange method.Finally,the precoding matrix can be optimized by the joint iteration method.The simulation results show that,compared to the suboptimal algorithm,the proposed algorithm can improve the performance of Bit Error Rate(BER).