Research On Interference Alignment Technology In LTE-A Multi-User MIMO Wireless Systems

With the rapid development of wireless communication technology,the interference is the key problem to improve the quality of communication and system capacity,then interference management approach becomes the main research in the field of wireless communications.As a new method to manage the interference between cells and users,interference alignment changed people's view of the capacity of the traditional Multiple-Input-Multiple-Output system,and become research hotspots in the wireless communication field.Interference alignment's core idea is to use the precoding technology at the base station to aligned the interference signal in one direction or space,and be orthogonal with the space that the desired signal map on.So the interference can be eliminated effectively.The key to achieve interference alignment is the precoding design,therefore,it's significant to study how to design the precoding matrix and optimize the precoding matrix.In this thesis,the research of the interference alignment begins with precoding matrix design with the iterative method and direct method and the interference alignment with limited feedback precoding matrix interference alignment in the MIMO communication systems and LTE systems.The details is as follows:Three kinds of precoding matrix design based on iterative method have been researched: minimizing the leakage interference algorithm,maximizing SINR algorithm and minimizing the rank of the interference matrix algorithm.The simulation results have been analyzed.It showed that when the degree of freedom of each user is 1,the maximize SINR algorithm has the best rate performance because of considering the desired signal power,and when each user gains 2 degrees of freedom,the minimizing the rank of the interference matrix algorithm has the best rate performance with the condition of high SNR.The precoding matrix design based on direct method has been researched,according to the comparing interference alignment algorithm don't use the total transmitting power of the system reasonably,the precoding matrix optimization method based on power distribution is proposed.The proposed method can reduce the influence of the interference signal to the desired signal and guarantee the receiving performance overall.The simulation results showed that the optimization algorithm can improve the bit error rate performance of the system with the little loss of the rate.In the real systems,Channel state information(CSI)is not completely known,the interference alignment with limited feedback in the circumstance of imperfect CSI has been researched.According to the high complexity and the large size of codebook caused by using single codebook to quantify the channel matrix in the traditional interference alignment with limited feedback,interference alignment with limited feedback based on double codebook is proposed.The simulation results showed that when the total number of the feedback bits are the same,this algorithm can achieve almost the same rate performance with the traditional algorithm,but the size of the codebook is much smaller and quantitative calculation is lower.In view of the rate of loss cause by the limited feedback system,the relation between the loss rate expression and the number of feedback bits has been deduced,and the bit allocation method based on lagrangian multiplier method is proposed,the simulation results showed that the bit allocation algorithm improves the rate performance compared with the traditional algorithm.