Research On Synchronization For OFDM System

Orthogonal Frequency Division Multiplexing(OFDM)has become the key technique in broadband wireless access and the next generation mobile communication system. Extensive attentions have been paid to OFDM due to its high spectral efficiency,high data rate and well anti-multipath ability.However, there are well-known shortcomings of OFDM technology: the timing offset and frequency offset is very sensitive. Timing offset causes inter-symbol interference, and frequency offset would destroy the orthogonality between subcarriers, causing ICI, which lead to a sharp decline in overall system performance. Therefore, it is necessary to research the effective timing synchronization algorithm and frequency synchronization algorithm to estimate and compensate for timing offset and frequency offset effectively, and try to minimize the negative impact on system performance. Therefore, research of this topic is necessary, and this paper is of great important academic value and practical significance.Firstly, the academic research background, the practical significance, the OFDM synchronization technology and the recent status were analyzed,and the basic principle of the OFDM system and synchronization were briefly introduced, And then the influence to the system performance of the symbol timing offset,carrier frequency offset was analyzed in detail to show the importance of the synchronization for OFDM systems.Seeondly, the ML algorithm based on CP in being is analyzed, the method of maximum likelihood estimation is adopted to jointly estimate symbol timing and carrier frequency offset. Base on the analysis, two improved ML algorithms are proposed. Simulation results show that the improved algorithms are better than the traditional algorithm in estimateing timing offset.In the end, many kinds of synchronization algorithlms are introduced and discussed in detail, such as Schmidl synchronization algorithm based on symbol timing and carrier frequency. Three improved algorithms are proposed to eliminate the timing plate of timing synchronization in SC algorithm. Simulation results show that the improved algorithms are better than the traditional algorithm in estimateing timing offset.