Research On Companding Scheme For Peak-to-Average Ratio Reduction In OFDM System

Orthogonal Frequency Division Multiplexing(OFDM)is widely used in the physical layer protocol of 5G mobile communication system due to its advantages of high spectral efficiency,strong anti-multipath performance and low implementation complexity.However,OFDM technology,as one of the multi-carrier modulation technologies in digital communication,also has a common defect of multi-carrier modulation technologies,that is,the peak-to-average power ratio(PAPR)is too high.However,in a wireless communication system,if the PAPR of the signal is too high,the amplitude of some signal sample points will exceed the linear amplification range of the power amplifier when the signal is amplified by the high power amplifier,which will cause the signal to introduce a large non-linearity.Linear distortion,which affects the bit error rate(BER)performance and power spectral density(PSD)performance of a communication system.In addition,an excessively high PAPR also reduces the power amplifier efficiency of the power amplifier,resulting in unnecessary energy consumption.Moreover,in order to meet the sharp increase in the demand for mass communication,the bandwidth and the number of subcarriers of the wireless communication system are increasing,so the problem of excessively high PAPR of the OFDM signal is also more serious.Therefore,in order to improve the communication quality and energy consumption of the wireless communication system,it is necessary to effectively reduce the PAPR of the OFDM system.Among many PAPR reduction algorithms,the companding algorithm has the advantages of low computational complexity and flexible adjustment,and the PAPR reduction performance and computational complexity of this algorithm have nothing to do with the number of subcarriers.Therefore,it is of great value to select the research of reducing the PAPR of OFDM system based on the companding algorithm.The main research work and innovative achievements of this paper are as follows:(1)This paper proposes a segmental companding and clipping hybrid algorithm.The paper first analyzes the advantages of segmented companding algorithm in companding distortion and algorithm complexity,and summarizes two design suggestions for companding algorithm based on the analysis results.Based on two design suggestions,this paper proposes a threesection companding and clipping hybrid algorithm,and obtains the companding function form with the smallest companding distortion by the variational method.The parameter selection of the algorithm is mainly based on the equilibrium constraints of algorithm complexity,companding distortion signal size and out-of-band radiation power size.The simulation results show that the segmented companding and clipping hybrid algorithm proposed in this paper has obvious advantages in BER performance and PSD performance compared with the comparison algorithm under the premise of effectively reducing PAPR,and the algorithm’s computational complexity is extremely low.(2)This paper proposes a piecewise nonlinear companding algorithm based on the reciprocal curve of the exponential function.The algorithm divides the target PDF function obeyed by the companded signal amplitude into two sections,and truncates the original amplitude distribution with the reciprocal curve of the exponential function that resembles the descending section of the Rayleigh distribution.In addition,the algorithm does not perform companding processing on low-amplitude signals,and maintains that the left segmental amplitude distribution of low-amplitude signals is still Rayleigh distribution,which reduces algorithm complexity and companding distortion.The algorithm benefits from the fact that the function adopted is close to the original Rayleigh distribution,so that the companding distortion introduced in the companding process is extremely small,and then its BER performance and PSD performance are theoretically excellent.In addition,based on the difference between the target PDF of the companded signal amplitude and the distribution function of the channel noise,this paper corrects the multiplier factor introduced by the channel noise when decompressing at the receiver.The simulation comparison results show that the piecewise nonlinear companding algorithm proposed in this paper is better than or equal to the comparison companding algorithm in PAPR reduction performance,and its BER performance is also better than the comparison companding algorithm in the two cases of decompression and nondecompression Companding algorithm,and the PSD performance of the algorithm is also superior.