Research On Key Technology Of Blind Demodulation For OFDM Signals

Orthogonal Frequency Division Multiplexing(OFDM)technology has the advantages of high speed,high utilization and high reliability.It has been widely used in various fields and is one of the mainstream modulation technologies on wireless transmission.The study of blind demodulation techniques for signals contributes to the supervision of communication resources and the establishment of a reliable communication environment.Compared with blind demodulation of single carrier signals,blind demodulation of OFDM signals is more difficult,requires more parameters,and requires higher synchronization requirements.Aiming at the blind demodulation of OFDM signals,the key technologies are studied,mainly including signal recognition,blind parameter estimation,and signal synchronization.Firstly,the process of blind demodulation of the signal is given on the basis of analyzing the modulation principle of OFDM.The OFDM signal recognition algorithm based on higher order statistics and cyclic prefix characteristics of the signal is studied,and the effectiveness of the algorithm is verified through simulation signal set.Secondly,the blind estimation algorithm for the main parameters of OFDM signals is studied.Based on the cyclostationarity analysis of OFDM signals,combined with cyclic spectrum and cyclic autocorrelation,the carrier frequency and chip time width are estimated using less computational effort.For estimating the effective length and cyclic prefix length of OFDM signals,an improved parameter estimation algorithm based on cyclic autocorrelation and sliding correlation is proposed.This algorithm does not require prior information and can achieve blind estimation of OFDM signal parameters in asynchronous state,and the performance is better than traditional algorithms.Then,the time frequency synchronization algorithm for OFDM signals is studied.The influence of synchronization error on blind signal demodulation is discussed,and timing synchronization algorithms based on maximum likelihood and set correlation are analyzed.Aiming at carrier frequency synchronization,an improved frequency offset correction algorithm for OFDM signals based on k-means clustering algorithm is proposed.Based on the traditional frequency offset estimation algorithm,the clustering algorithm is introduced to estimate the constellation phase offset and then calculate the subtle frequency offset,which improves the accuracy of the carrier frequency synchronization algorithm.Finally,the blind demodulation system for OFDM signals based on VS2010 is introduced,including its interface design and workflow.And the system is tested with simulated and actual signals.