Research On PAPR Reduction Algorithms Of Large Scale MIMO-OFDM System

With the rapid development of information and communication technology,requirements of users for transmission rate and reliability are raising.The future communication system is facing greater challenges.Multiple-Input Multiple-Output(MIMO)-Orthogonal Frequency Division Multiplexing(OFDM)technology combines the advantages of MIMO and OFDM.It can significantly improve the throughtput,reliability and frequency band efficiency of the system.It has become the key technology of the new generation of wireless communication system.However,the Peak-to-Average Power Ratio(PAPR)of OFDM time-domain signals is usually high,which means that the amplitude fluctuation range of the signal is large.The OFDM signal can easily enter the saturation region of power amplifier,which causes nonlinear distortion and affects system performance.This problem is more difficult in largescale MIMO-OFDM systems.Therefore,how to effectively reduce PAPR in OFDM systems is the focus of research in the field of communication.In this thesis,the main contents are as follows:(1)PAPR problems in OFDM systems and traditional PAPR reduction techniques are introduced.PAPR problems in large-scale MIMO-OFDM systems are also introduced.In large-scale MIMO-OFDM systems,a large number of antennas provide additional degrees of freedom.Based on this,an appropriate precoding method can be found,which is able to effectively reduce PAPR of the OFDM signal and suppress Multi-User Interference(MUI).(2)The objective function is to minimize carrier distortion of OFDM signal data.The precoding matrix,PAPR and free carrier power are used as constraints to establish a nonconvex optimization model.After introducing auxiliary variables,the Alternating Direction Method of Multipliers(ADMM)is used to solve the optimization model.The algorithm of Minimize Signal Distortion based PAPR Reduction(MSD-PAPR)is propesed.Simulation results show that the MSD-PAPR algorithm can greatly reduce the PAPR of OFDM signals and almost reach the ideal Bit Error Rate(BER)performance with the introduction of small controllable distortion.(3)In order to enable all variables to be solved in parallel and reduce the computational complexity of MSD-PAPR algorithm,the construction method of optimization model is improved in this thesis.An Improved Minimize Signal Distortion based PAPR Reduction(IMSD-PAPR)algorithm is proposed in this thesis.The algorithm has fewer solving variables.Each variable can be parallelized.It is easy to implement by hardware and can greatly improve the efficiency of algorithm execution.Simulation results show that IMSDPAPR algorithm has lower computational complexity than MSD-PAPR algorithm.In other words,IMSD-PAPR algorithm performs fewer iterations when achieving the same error-bit performance and better Out-of-Band Power(OBP)performance.