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Currently, OFDM (orthogonal frequency division multiplexing) technology in the field of wireless communication has been widely used, mainly because of high spectrum efficiency of OFDM technology, the data transfer rate is high, effective against multipath interference and narrowband interference and many other advantages. However, the OFDM system includes symbol timing offset and frequency offset, including the synchronization mismatch is very sensitive. Synchronization error signal generation data may be received phase shift of the attenuation data, a data cyclic shift, inter-symbol interference and inter-channel interference and other adverse effects, therefore, synchronization can work OFDM system is a key factor. As in the uplink OFDM PAPR problem difficult to solve, and is currently used more for OFDM downlink. Therefore, in-depth study of the downlink synchronization in OFDM systems is important. Based on the study of various synchronization training sequence is proposed based on a cascade the two OFDM symbols generated OFDM synchronization training symbols, the two OFDM symbols, a non-positive, the symbol, the symbol a is positive. Compared to some of the existing synchronization training sequence structure, which requires less training symbols of the OFDM symbols, so there is the advantage of low data overhead. Because the asymmetry of two OFDM symbols, the training symbols can be applied to timing synchronization and frequency synchronization, the increase in the performance and reduce the synchronization estimation computational complexity. Research on timing synchronization, we propose a \This method of using the proposed training symbol synchronization, timing synchronization with the conventional method, a plurality of correlation peaks merge, generating the estimated timing of the peak position deviation. For each sampling point in only 9 times the complexity of complex multiplication in the case, the various SNR has a better synchronization performance. Frequency synchronization in the study, the paper proposes a frequency synchronization method: \The algorithm in order to be able to lower computational complexity, the mid-range frequency offset estimation to solve the problem, the use of the proposed training symbol synchronization delay autocorrelation correlation values ??generated by the phase angle, after the merger, to obtain two initial frequency biased estimates, combined with the knowledge of number theory, be combined estimated frequency offset. Through computer simulation, when selecting the appropriate parameters of the program, you can get a larger frequency offset estimation range, the computational complexity than traditional algorithms, but you can get better frequency estimation minimum mean square error performance. This synchronization comprehensive training symbols, the \The program is including synchronous training symbol generation, coarse timing synchronization, fractional frequency offset estimation, the integer frequency offset estimation and fine timing synchronization, including a complete solution. With a lower computational complexity, and the advantages of lower estimated error rate in OFDM system has a high application value. Synchronous technology is a digital mobile communication system is one of the key technologies, there are many important research direction, this paper on which the timing synchronization and frequency synchronization issues to do some research. In MIMO-OFDM (multiple input multiple output orthogonal frequency division multiplexing) system synchronization, multi-cell, multi-user synchronization direction in case there are many issues worthy of further research to address and uplink MIMO-OFDM system synchronization of OFDM systems.
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