Research Of PAPR Reduction Methods In Large Scale MIMO-OFDM Systems

Massive Multiple-input Multiple-output(MIMO)and Orthogonal Frequency Division Multiplexing(OFDM)are two important techniques of Fifth Generation(5G)system.Massive MIMO-OFDM system,which combines the advantages of two techniques has broad prospects for development.Since OFDM modulation technique is a multi-carrier technique,reducing high Peakto-average Power Ratio(PAPR)is a fundamental problem in massive MIMO-OFDM systems.High PAPR brings three problems.(1)After being input to the Radio Frequency(RF)power amplifier,if the signal power is not in the linear region,it is prone to nonlinear distortion,which resulting in inband distortion and out-of-band radiation;(2)Causes the efficiency of the RF power amplifier to decrease;(3)It requires a higher dynamic range for Digital-to-Analog Converter(DAC),which resulting in a decrease in the efficiency of DA conversion.The PAPR suppression technique is effective in reducing the PAPR of signals in OFDM systems.Since single-antenna OFDM system is the basis of massive MIMOOFDM systems,the dissertation first studies the MIMO system and OFDM technology,introduces some classical PAPR suppression methods.Then the PAPR suppression methods for massive MIMO-OFDM systems are discussed.Finally,two effective PAPR suppression methods are proposed for the system mentioned above.First of all,a PAPR reduction method based on channel characteristics in massive MIMO-ODFM system is proposed.The method utilizes the high degree of freedom brought by massive MIMO,combines the matrix Null space theory to derive: adding a calculated vector to original signal not only ensures that the received signal is not changed with sideband information saved,but also can reduce the PAPR of the system.At the same time,in order to reduce the complexity of algorithm,a sub-optimal method of the method is provided.Simulation results show that the proposed methods have good PAPR reduction effect and low algorithm complexity.Secondly,a precoding design for low PAPR in massive MIMO-OFDM systems is proposed.The method is based on linear precoding methods in massive MIMO systems,and designed precoding matrices that can eliminate Multiuser Interference(MUI)and reduce PAPR.In addition,to reduce the computational complexity,the dissertation also provides a sub-optimalmethod for the precoding method.Simulation results verify the effectiveness of the proposed precoding method in PAPR suppression.The methods proposed have been verified by MATLAB simulation,can be used to reduce PAPR in massive MIMO-OFDM systems.