Research On Signal Preprocessing And Beamforming Methods For Millimeter Wave Massive MIMO Under Non Ideal Hardware Conditions

With The rapid development of wireless Mobile Communication technology,The5 th Generation Mobile Communication System(5G)has already been commercialized,and ultra-5G has also stepped into the forefront of research.As three key technologies in today’s and future mobile communication,millimeter wave communication has a large number of frequency band resources and can serve millions of devices at the same time.Multiple Input Multiple Output(MIMO)uses hundreds of antennas,which can effectively compensate for the high path loss caused by millimeter wave communication.As one of the important technologies of beamforming,precoding preprocesses signals through channel state information to eliminate multi-user massive MIMO interference and improve gain.The three technologies complement each other and greatly improve the efficiency of communication transmission.However,the gain of the power amplifier is not linearly increased in the RF antenna of the actual massive MIMO communication system.Therefore,based on the above background,thesis considers the millimeter wave massive MIMO nonlinear power amplifier multi-user communication system,and studies the two technologies of precoding and power signal processing,and makes the following contributions:In the study of precoding technology,a gradient ascent algorithm combining joint gradient ascent and iterative search is proposed to maximize the total rate and the problem.The simulation results show that the algorithm can achieve the performance improvement of about 5 bps/Hz under the condition of low input power,low number of users and low number of transmitting antennas,but the performance improvement is very limited under other conditions.Therefore,in order to solve this problem,another algorithm based on Rayleigh entropy is proposed to maximize Signal Leakage plus Distortion plus Noise Ratio(SLDNR).After the algorithm maximizes the total rate and the problem is approximated to maximize the SLDNR problem,the problem is processed using the method of Rayleigh entropy solution.The simulation results show that the proposed algorithm can greatly improve the system performance,and the improvement range can reach 16 bps/Hz.In the power signal processing technology,firstly,aiming at the problem that the system performance deteriorates rapidly under the condition of high input power,the optimal total power approximation algorithm is proposed to approximate the system to the optimal input power state.Secondly,in order to further improve the performance of the system,the power distribution gradient rise algorithm is proposed,which replaces the precoded signal with the power signal on the basis of the first gradient rise precoded algorithm,and then we derive it.Finally,combining the advantages of the two technologies,a joint algorithm is proposed that combines the optimal total power approximation algorithm and maximizes the SLDNR algorithm and the power distribution gradient rise algorithm,which can greatly improve the speed of the millimeter wave massive MIMO nonlinear power amplifier system while reducing the power consumption,and the increase amplitude can reach about 17 bps/Hz.And the improvement is more obvious when there are more users.