Research Of Timing Synchronization And Frequency Offset Estimation In OFDM System

Orthogonal frequency division multiplex (OFDM) is a kind of multi-carrier transmission technique. It has been taken as a major technique for the next generation communication system as well as4G, because it can provide high-speed data transmission in complex wireless channels with high spectrum efficiency and the capacities to resist frequency selective fading and inter-symbol interference (ISI), however, OFDM is very sensitive to synchronization error. The emergence of the timing error and carrier frequency offset in the system will result in inter-carrier interference (ICI) and ISI, which affect the overall performance of the system. Thereby synchronization technique has drawn much attention in modern communication field.At first, this paper elaborates on the OFDM technique principle and significance of study synchronization technology in detail, and analyzes the impact brought by the symbol timing offset and carrier frequency offset in OFDM systems by the way of theoretical analysis and computer simulation.The main part of the paper focus on the study of the symbol timing synchronization and carrier frequency offset synchronization algorithm. Firstly, the classical synchronization algorithm has been studied penetratingly, and then the improved symbol timing synchronization algorithm based on amplitude zero auto-correlation (CAZAC) is proposed. The conjugate symmetric structure of the improved algorithm makes an impulse-shaped timing measure curve, and the synchronization information contained in the cyclic prefix is utilized to reduce the adverse effects brought by the sequence structure to timing estimation accuracy of side peaks. The proposed algorithm effectively overcomes platform phenomenon and much spike phenomenon resulted from Schmidl&Cox (S&C), Minn and Park algorithms, in timing estimating. Secondly, the carrier frequency synchronization algorithm has been researched and analyzed. At the foundation of the improved timing estimation, improved carrier-frequency synchronization algorithm is proposed. The improved carrier-frequency synchronization algorithm has higher precision of frequency offset estimation, and integer frequency offset is estimated in time domain without FFT calculation, reducing the system cost.