Research On Precoding And Correlative Technology Of Large Scale Antenna System

With the rapid growth of the number of wireless terminals,the contradiction between the capacity demand of wireless communication networks and the limited spectrum resources is becoming more and more obvious.As one of the key technologies of the fifth generation mobile communication technology,Large-scale Antenna(LSA)can effectively improve the capacity performance of the system.LSA puts a lot of antenna elements in a small area.It is bound to introduce certain interference.Therefore,the precoding technique should be used to eliminate the interference.It is also an effective technique to resist multipath fading in wireless communication technology,which can also reduce the complexity of signal processing at the receiver.This paper focuses on the research of precoding and related technologies in large-scale communication systems.In this paper,the system model of LSA downlink transmission is introduced.Based on this model,aiming at the high complexity of matrix inversion in zero forcing(ZF)precoding,we introduce several low complexity precoding algorithms which iteratively approach ZF precoding scheme.And these algorithms are suitable for narrow band channels.Next,a low-complexity recursive convolution precoding method in the downlink transmission link of LSA-OFDM system is studied in detail.The recursive method is used to avoid the direct calculation of the inverse of the matrix,and then it is converted into a precoding filter in the time domain.And the precoded filter coefficients can also be calculated by recursion.Because precoding processing is carried out in time domain,the number of inverse Fourier transform is equal to the number of users in the system,but it has nothing to do with the number of antennas at the transmitter side.The algorithm can effectively reduce the complexity of the precoding complexity of LSA-OFDM system and the processing complexity of inverse Fourier transform,and can effectively track the time-varying channel.It is assumed that the channel is not time-varying when the user updates the system.In view of the user update problem,a design scheme is proposed to simplify the system precoding after user update.The scheme can effectively reduce the complexity of user pre update processing after updating.Finally,the precoding design based on Quality of Service(QoS)is mainly studied,that is,the user's QoS needs are met by the precoding vector and the dynamic user power allocation.The joint solution of the two is more difficult.Therefore,it is converted into two steps to solve the problem,that is,to determine the precoding vector of the user first,and then to satisfy the user's demand by power allocation.This paper focuses on the following situation: in view of the user update in the time-varying channel,a precoding algorithm is proposed to simplify the low complexity of the user's update system by using the prior information.Simulation results show that the low complexity algorithm can effectively reduce the complexity of precoding and track the time-varying channel effectively.However,the performance of the system will deteriorate with time,so we need to increase the sending power of the sending side to meet the QoS needs of users.