Research On Iterative Symbol Timing And Carrier Synchronization Of Ofdm System

Orthogonal frequency division n multiplexing (OFDM) is key technology for the fourth-generation mobile communications systems. One of its advantages is that it has high spectrum efficiency and is robust to the multi-path fading. However, OFDM is very sensitive to both symbol timing and carrier frequency offset, so it is probably to produce inter-carrier interference. Thus, in the OFDM system, symbol timing and carrier frequency offset are the main factors which affect the system performance. This paper makes a research of symbol timing and carrier frequency estimation for OFDM systems based on OFDM model.First of all, this paper describes the effect of the symbol timing and frequency offset to the system in detail, and analyses some classic frequency and symbol timing synchronization algorithms and these algorithms are simulated by MATLAB.Secondly, Maximum Likelihood (ML) method which is based on the Cyclic Prefix (CP) has been researched thoroughly. Aiming at solving the problem that the frequency offset estimation is not accurate due to the wrong estimation of symbol timing synchronization, the paper makes some research from the follow improvement for ML algorithm based on CP. The improved algorithm estimates three consecutive symbols at the same time. The algorithm uses observation window in order to reduce the frequency offset error, in which average of every frequency offset estimation values of three symbols is obtained during frequency offset estimation. This paper compares the improved algorithm and the original algorithm in the symbol timing estimation by MATLAB. Simulation of the improved algorithm show that this algorithm reduces the frequency offset estimation error which is caused by the inaccurate symbol timing estimation.Finally, because the multipath channel for OFDM symbol timing synchronization caused great influence in timing synchronization. The error of timing estimation of ML method is reduced with the iteration of timing estimation, so as to improve the accuracy of the timing estimation. The simulation shows that iterative synchronous estimation is feasible through analysis of calculation and computing speed.