Research On Papr Reduction Techniques Of Massive MIMO System For 5G

The mobile communication system has stepped into the 5G era.Mobile communication system of 5G will play a great role in more abundant application scenarios and can provide an exceedingly new user experience.At the same time,it also puts forward higher requirements for the spectrum efficiency and power efficiency of communication systems.Massive MIMO systems,deploying massive antenna arrays at the base stations,can not only improve the spectrum efficiency and the communication quality of the system significantly,but also reduce the interference between users and the transmitting power of the base stations effectively.However,the peak to average ratio of OFDM signals is a key problem to be solved urgently in this system.In this paper,the crucial contributions are as follows:Original data streams in large-scale MIMO systems need to be passed through a precoder to reduce interference among users.Due to the deployment of large antennas at the base stations,there are infinite number of feasible precoding schemes in the system and different precoding schemes will produce different transmit signals.Therefore,to seek a kind of precoding scheme which can reduce the interference between users as well as generate signals with low PAPR,is a good idea to solve the problem of PAPR in large-scale MIMO systems.We established a model of PAPR reduction based on precoding and in view of this model,two PAPR reduction schemes based on precoding are proposed:(1)a split-Bregman algorithm framework is used to solve the problem.The algorithm framework uses the split technology and the traditional Bregman iterative algorithm,which has fast convergence speed and low algorithm complexity.(2)using the improved ADMM algorithm framework.The transmit data are divided into two groups according to the antennas,and in each antenna group,the firing data are divided into several parallel sub problems.Simulation results show that the scheme has faster convergence speed.Due to the difference between the number of transmitting antennas and receiving antennas in large-scale MIMO systems,there is an extra channel space which is completely orthogonal to the transmission channel of the system,that is,the null space.At the same time,the traditional clipping scheme is the most direct method to reduce PAPR and it superimposes the original signal and the clipping noise.Therefore,there will be no distortion of the transmitted signal after clipping if we can guarantee that the clipping noise is distributed in the null space of the transmission channel.Based on this idea,the concept of null space coding is proposed and a model of PAPR reduction based on null space coding is established.Moreover,in order to reduce the influence of the power of the clipping noise on the SNR of the received signal,the power of the clipping noise is minimized as the target of the problem,and the PAPR of the final transmitted signal is used as a constraint.This paper uses ADMM algorithm framework to solve it and the final simulation results show that the proposed scheme based on null space has lower complexity and better performance on BER.