| OFDM is a high-speed multi-carrier transmission scheme, which is robust to multipath fading and high spectrum efficiency. As a new technology, it attracts wide attention and has been adopted in many wide-band wireless digital communication standards.OFDM systems contain more than one orthogonal sub-carrier, so it is different from single carrier systems. Synchronization error will lead to inter symbol interference as well as inter carrier interference. Therefore, synchronization is extremely crucial to OFDM systems. Symbol synchronization is used to confirm OFDM symbol's initiative position for accurate demodulation.Symbol non-synchronization will probably lead to serious ISI. If symbol synchronization is not good, the whole system's performance will decrease because frequency offset estimation and timing tracking is run after it. Therefore, symbol synchronization is an important part of OFDM system's synchronization. This paper firstly introduces the history and recent development of OFDM, the important status of synchronization in OFDM system, the domestic and overseas recent research status of synchronization. Secondly, we introduce the relational knowledge of wireless channel, the system model and basic theory of OFDM, also analyze OFDM signal's design rules. Thirdly, we introduce diversified synchronization errors, the influence of timing offset, carrier wave offset, sampling rate offset on OFDM system's performance, existing diversified synchronization algorithms, then analyze several algorithms based on cyclic prefix and pilot sequences and their performances including their maximal correlation algorithms and minimal average square algorithms by simulation. The algorithms based on pilot sequences are simple and their synchronization error is relatively low, but the system's validity falls. Losing step will lead to the whole frame symbols mistake. A new algorithm basing on cyclic prefix is presented at last. It is a short sequence adaptive synchronization algorithm. Minimum mean square error is replaced by minimal square error in the algorithm. Symbol synchronization is made up of coarse synchronization and fine synchronization. First, symbol's coarse synchronization is realized using a part length of cyclic prefix. Then, symbol's fine synchronization is realized using the whole length of cyclic prefix. And the algorithm can automatically regulate the size of synchronization's slip window according to the length of OFDM's effective data. When other performance indexes is fixed, the algorithm greatly decreases the mounts of calculation and shortens the synchronization establishing time. |
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