Research On Papr Reduction Scheme Based On Predistortion Technology In OFDM System

In wireless communication systems,orthogonal frequency division multiplexing technology is widely used in 4G,IEEE 802.11,DVB,WiMAX standards or systems because of its high spectrum efficiency and strong anti-multipath fading ability.However,there is a problem of high PAPR in OFDM system,which will degrade the system performance.Therefore,reducing PAPR effectively can make OFDM more widely used.At present,there are many effective PAPR reduction technologies for the problem of PAPR in OFDM system.This paper focuses on the clipping technology and companding transformation technology,and puts forward the corresponding improvement scheme according to the shortcomings or defects of these two technologies.In clipping technology,this paper proposes a elimination of clipping distortion scheme for OFDM systems by compressed sensing based on distance metric.Firstly,aiming at the complexity of orthogonal matching pursuit(OMP)algorithm in the process of reconstructing the clipping distortion,we design a decision criterion to obtain the rough estimation set of clipping position.Using the clipping position information in the set,we design an OMP algorithm based on distance vector.The improved algorithm effectively reduces the computational complexity of OMP algorithm.Then,aiming at the accuracy of clipping distortion recovery,we propose a receiving structure for iterative recovery of clipping distortion.This structure uses the recovered clipping noise to continuously update the observation data,so as to reconstruct the clipping noise more accurately.Simulation results show that the scheme significantly improves the accuracy of denoising and has good adaptability in different channel environments.In the companding technology,aiming at the problem that the traditional companding technology will bring nonlinear distortion,a nonlinear companding scheme based on quadratic function is proposed in this paper.In this scheme,the probability density function(PDF)of OFDM signal is redesigned as a piecewise function.For small amplitude signals,the original rayleigh distribution of PDF is not changed.For medium and large amplitude signals,the PDF is defined as a quadratic function,and the corresponding companding function is derived.The companding function provides three independent companding parameters under the constraint of keeping the average signal power constant before and after companding,which can achieve a good tradeoff between PAPR gain and bit error rate.Simulation results show that compared with some existing companding schemes,the proposed scheme shows better bit error performance under the same PAPR suppression level.At the same time,we propose a joint PAPR reduction scheme based on clipping and companding technology.In the proposed joint scheme,the signal is companded and clipped at the transmitter,and the clipping distortion recovery algorithm is used for the received signal at the receiver.From the simulation results,we can find that the proposed algorithm can not only effectively reduce the PAPR,but also greatly improve the bit error performance of the system.Finally,we summarize the paper and point out some areas that still need to be improved.