Research On Precoding Optimization Algorithms For MIMO Relay Communication Systems

Multiple-input and multiple-output(MIMO)technique provides significant performance gains in the spectral efficiency and link reliability owing to multi-antenna has transmission mode for diversity and reuse.However,the MIMO relay technology can effectively solves the problem of information coverage and increases the probability that the users of blind area can receive signal,then the communication quality of the system can be improved.In addition,the MIMO relay technology combining with the precoding technology can decrease signal interference and reduces bit-error rate(BER)of the system.An effective precoding algorithm is critical to improve the performance of wireless communication systems.In this paper,we mainly research the design of the precoding algorithm under the following three communication models,including the multi-relay symmetric MIMO communication system,the transmitter/receiver multi-user MIMO relay communication system with direct links and the multi-user two-way MIMO relay communication system.The main purpose is that we design a feasible precoding algorithm for MIMO relay communication system to further improve performance of the system.The main work of this paper is as follows:1.In a scenario for multi-relay symmetric MIMO communication,considering the problems of high complexity,centralized manner and big feedback overhead for existing relay algorithms,a low-complexity and diversity diagonalizable relay algorithm is researched.The maximum mutual information(MI)is taken as the design criterion with all relay power constraint.Considering the specialization of the objective function expression,the objective function can be maximized by diagonalizing the matrix of the determinant.The objective function is constituted with the sum of multiple diagonal matrices by eigenvalue decomposition(ED)and singular value decomposition(SVD),so each relay precoding matrix is solved separately,based on which the form of the each relay precoder is derived.Simulation analysis verification,the researched algorithm in this paper comparing with the existing algorithms has a low-complexity and can obviously improve capacity of the system.2.In a scenario for transmitter/receiver multi-user MIMO relay communication,aiming to the problem that ignoring the direct links between the transmitter and the receiver can lead to performance loss for the system,a joint iteration algorithm that all precoding matrices of transmitting users to be intensively optimized is developed based on the design criteria of the minimum the sum mean-square-error(MSMSE).Firstly,the transmitting multi-user for the input of multi-streaming are equivalented as a base station for the input of single-streaming to optimize,the precoding matrix of the base station consists of the sub-precoding matrix of all transmitting users.Secondly,the non-convex MSMSE optimization problem is transformed into two sub-convex optimization problems to solve respectively,for each sub-convex optimization problem,we choose Karush-Kuhn-Tucker(K.K.T)conditions and CVX optimization toolbox to solve.Simulation analysis verification,the researched algorithm has an obvious improvement in the SMSE performance than other existing algorithms,and in the low signal to noise ratio(SNR)range,algorithm has a best BER performance.In addition,it has a fast convergence within 10 iterations.3.In a scenario for multi-user two-way MIMO relay communication,the two-way relaying can make up for the deficiency of the one-way relaying.Considering an individual optimization of the precoding problem for the base station and all users,we improve a novel Four-Step iterative algorithm,which the MSMSE is taken as the design criterion.Algorithm transforms the non-convex MSMSE optimization problem into four sub-convex optimization problems to respectively optimize source precoding matrix,user precoding matrix,relay transceiver matrix and receive filter matrix.According to the semi-definite programming(SDP)and square constrained quadratic programming(QCQP),combining with CVX optimization toolbox to solve the equivalent optimization problem,and algorithm simplify the complexity of mathematical operations.Simulation analysis verification,the Four-Step iterative algorithm can significantly improve SMSE performance than the Tri-Step iterative algorithm.In addition,the algorithm has a fast convergence.