Research On The PAPR Reduction Of OFDM Systems Based On Companding Operation

Orthogonal frequency division multiplexing(OFDM)is widely applied in communication systems,such as 5th generation(5G)),beyond 5G(B5G)and 6th generation(6G)owing to its high spectral efficiency and robustness to multipath interference.However,OFDM systems suffer from high peak-to-average power ratio(PAPR).A high PAPR will cause the OFDM signal samples to have high distortion when passing through a power amplifier(PA),which will reduce the PA efficiency.Finally,the OFDM signal transmission efficiency is influenced.Therefore,PAPR reduction is an important research topic in OFDM systems.Companding is attractive for PAPR reduction in OFDM transmissions based on modern and future communication systems such as 5G/B5G/6G.Because it is simple and effective for PAPR reduction.It can also balance the performance of PAPR reduction,BER performance,power spectral density(PSD)performance and computatinoal complexity.This paper investigated the PAPR reduction scheme for OFDM systems based on a companding operation,which are implemented with the methods of the combination of theoretical modeling,parameter solving,performance analysis,simulation results,etc.It is composed of four contents,including the design of piecewise linear companding function,hard-clipping-based piecewise nonlinear companding function,soft-clipping based piecewise nonlinear companding function and low complexity nonlinear companding function for PAPR reduction in OFDM systems.The investigation explores a series of companding schemes for PAPR reduction in OFDM systems from multi-level perspective.The study results provide a reference for the optimal companding design as well as parameter selection for companding based PAPR reduction scheme used in OFDM systems for modern and future communication systems such as 5G and 6G systems.The main contribution of this paper is given as follows:1)It provided a hybrid of companding and clipping scheme for PAPR reduction in OFDM systems.In the proposed companding scheme,signal samples with large amplitudes are clipped for peak power reduction.Signal samples with small apmlitudes are amplified for power compensation.This paper builds constraint optimization problem for choosing appropriate parameters for the proposed companding scheme.The constraint condition is the average signal power constant before and after companding while the optimization goal is companding distortion and out of band radiation.2)This paper designed a hard-clip-based continuous nonlinear piecewise companding(CNPC)function for PAPR reduction in OFDM systems.During the full signal processing,this paper did not compand the signals with small amplitudes to avoid unitary companding,which is effective in reducing the companding distortion as well as the computational complexity.For the signal samples with large amplitudes,this paper used a hard clip to restrain the peak OFDM signal power.For the medium-amplitude signals,this paper used a quartic polynomial to compensate for the companding operation power loss.3)This paper designed a soft-clipping-based piecewise nonlinear companding scheme for PAPR reduction in OFDM systems.For the proposed companding scheme,this paper did not change the probability density function(PDF)of the signals with small amplitudes.For the signals with large amplitudes,this paper designed the PDF of the companded signal amplitudes as a sine distribution.Then,we can find the companding function based on the PDF of the original and companded signals.4)This paper designed a low-complexity companding function for PAPR reduction in OFDM systems.Compared with piecewise function,it reduced the computational complexity for piecewise comparison.We first design the PDF of the companded signals,whose corresponding cumulative distribution function(CDF)is an arcsine function,and then we can determine the companding function based on the CDF of the original and companded signals.