Research And Simulation On Timing And Frequency Synchronization Algorithm In OFDM System

Orthogonal Frequency Division Multiplexing (OFDM) is a highly-efficient multi-carrier modulation technology. The great advantage of OFDM is that it improves frequency utilizing rate simultaneously and that it is robust against frequency selective fading. So it is suitable for high speed wireless transmission, and it is considered as a Key technology in 4G communication. However, OFDM systems are extremely sensitive to synchronization error. When synchronization error exits, Serious Inter-Carrier Interference and Inter-Symbol Interference are introduced and demodulation performance will be degraded greatly. So eaccurate synchronization is essential to OFDM system.This paper mainly addresses synchronization algorithms in OFDM system. This paper first introduces the basic theory and characteristic of OFDM system, including the orthogonality between the sub-carrier for OFDM system, the realization of OFDM system based on IDFT/DFT and the structure of OFDM symbol with Cyclic Prefix (CP).Next the effects of symbol timing error and the carrier frequency offset on the performance of OFDM system are discussed in theory, and the importance of synchronization is illustrated.I mainly research Maximum Likelihood (ML) algorithm based Cycle Prefix (CP) and some improved algorithms. A lot of computer simulations are given over Additive White Gaussion Noise (AWGN) and frequency selective fading channels. We analyze and compare the performance of a few synchronization methods, including their applied areas, merits and shortcomings.Based on the analysis, the ML algorithm is improved. Simulation results show that the estimation error of improved algorithm is much lower than that of the conventional ML method in multi-path channel.In the end, the characteristic of training symbol and the principle for Schmidl&Cox algorithm and improved schemes are discussed.Based on the analyses of the existing algorithms and cyclic prefix (Cyclic Prefix) and training symbol of the relevant information , the Schmidl&Cox algorithm is improved, Simulation results show the improved algorithm overcomes the defect in timing synchronization of the traditional Schmidl&Cox algorithms, and also improve the symbol timing and frequency offset estimation performance...