Study On Frequency And Timing Synchronization For OFDM System

OFDM is the key technique for the fourth generation (4G) mobile communication. The great advantage of OFDM is that it is robust against frequency selective fading and that it improves frequency utilizing rate simultaneously. But OFDM is very sensitive to frequency offset and phase noise. Lack of carrier synchronization, the orthogonal character of sub channels will be destroyed, it will introduce sub carriers'disturbance ICI. The error of symbol timing synchronization will introduce ISI, and it will have serious effects on channel estimation. There are three kinds of synchronal modes in OFDM system: symbol timing synchronization, carrier synchronization, sampling-bell synchronization. This paper chiefly studies symbol timing synchronization and carrier synchronization.A brief discussion of wireless channels provides channel model to the following study of the OFDM system. This article created a simple OFDM system and validated the performance of OFDM system based on IFFT/FFT through analyzing the various processes of creating signal.The structure of the system model is the basis of this article to study on the symbol timing and carriers synchronization. The article gives theoretical analysis on the effect of symbol timing and carriers synchronization error, and gives results of impact of receiving signals constellation in MATLAB simulation environment.In view of these problems, several classic algorithms of symbol timing and carriers synchronization are introduced. MLE algorithm has a good performance over AWGN channels, but it gets wrong estimate over multipath fading channels due to the destruction of the guard interval data; the limit of the acquisition range of Moose's algorithm for carrier frequency offset is±12 the subcarrier spacing. On the analysis of these algorithms some new improved algorithms are presented. Simulation results show that these improvements enhance the OFDM synchronization performance.In addition most of the parameters used in simulation accord with the ESTI DVB-T 2K mode standard, this reflects the practical value of this study.