The Study Of Timing And Frequency Synchronization Technique For OFDM

Orthogonal Frequency Division Multiplex (OFDM) is a kind of efficient modulation mode. Due to its good ability in coping with multi-path fading and optimum spectrum efficiency, OFDM is widely used in wideband wireless communication. OFDM system is sensitive to symbol timing and carrier frequency offset very much, so that it is probably to produce inter-carrier interference. Therefore precise timing and frequency offset estimation and compensation is very important in OFDM communication system. Synchronization becomes one of major research topics in this domain.In the practical application, in order to get good performance, strict synchronization is needed in OFDM systems. So, synchronization becomes one of the key issues related to OFDM performance.The basic principle and system structure of OFDM is illustrated in this paper. It focuses on the effect, which is caused by synchronization error, to the performance of OFDM. At the same time, the recent research is reviewed in the field of OFDM. An improved algorithm based on the training sequence is introduced.Because of the existence of'plateau'in the Schmidl algorithm, symbol timing is not very accuracy, and variance is very high. Based on the analysis of conventional method (Schmidl algorithm), the improved algorithm redesigns a modified training symbol. This algorithm can improve the synchronization performance to some extent. The simulation results show that the improved algorithm not only possess better timing synchronization performance than the conventional method, but also ensure higher accuracy of frequency synchronization estimation in both AWGN channel and multipath channel.However, no algorithm is perfect. The range of fraction Frequency offset (FFO) estimation is narrow. When FFO is more than half of sub-carrier spacing, the performance of frequency offset estimation decline significantly.