Frequency Offset Estimation Of OFDM-IM Based On Null Subcarriers Under Rayleigh Channel

In a multi-carrier communication system,due to the Doppler effect and the mismatch between receiver and transmitter,each carrier of the multi-carrier system will cause carrier frequency offset(CFO),resulting in the destruction of the orthogonality between the subcarriers,causing inter-carrier interference and affecting the system performance.The Orthogonal Frequency Division Multiplexing(OFDM)technology is widely used in multi-carrier wireless communication systems with its high spectral efficiency and ability to resist multipath interference.Base on OFDM,Orthogonal Frequency Division Multiplexing with Index Modulation(OFDM-IM)technology has gradually become a competitive modulation method.However,OFDM and OFDM-IM wireless communication systems are sensitive to CFO,which affects the reliability of communication.Therefore,CFO estimation and compensation have become one of the research directions of OFDM technology.We often use a multipath model to describe the channel.Compared with the determined channel,the amplitude attenuation coefficient of each path of the Rayleigh channel is a random variable.In the approximate calculation of the mean square error of the frequency offset estimation value,the complexity also increases.This article will take the Rayleigh channel as the background,and mainly carry out the following work around the frequency offset estimation based on the null subcarrier:1.The mean square error is selected as the performance evaluation parameter of the frequency offset estimation,and from the perspective of parameter estimation,the explicit derivation and theoretical analysis of the approximate expression of the mean square error are carried out.Among them,when deriving the theoretical value of the mean square error,we give approximate expressions of different accuracy based on Taylor series expansion,and use corresponding examples to verify.2.The traditional frequency offset estimation algorithm is briefly introduced,and the advantages and disadvantages of the specific estimation performance are analyzed.Subsequently,this article studies the OFDM frequency offset estimation algorithm based on null subcarriers,and discusses the setting and function of null subcarriers in detail.Among them,after performing related simulations,we analyzed the performance improvement of null subcarriers,and showed that on the basis of ensuring higher energy efficiency,the method can be further optimized through the inactive subcarrier detection of OFDM-IM frequency offset estimation performance.3.It is proposed to apply inactive subcarrier detection to OFDM-IM frequency offset estimation under Rayleigh channel to improve the accuracy of frequency offset estimation without subcarrier detection.In this paper,certain research and analysis have been carried out on the energy threshold of subcarrier detection,and after a compromise between the probability of error detection and the accuracy of frequency offset estimation,a suitable energy threshold has been selected.Through specific simulation experiments and theoretical comparisons,this paper verifies that the estimation algorithm has improved estimation accuracy compared with the OFDM frequency offset estimation scheme based on null subcarriers under high Signal-toNoise Ratio(SNR).Compared with the frequency offset estimation scheme based on null subcarriers,this algorithm adds a smaller computational complexity to obtain performance improvements.