中文摘要：

提出了在直接检测光正交频分复用（DD—O—OFDM，directdetection—optical—orthogonalfrequen—cydivisionmultiplexing）传输系统中使用格雷对训练序列做定时同步算法。新算法利用格雷对的非周期自相关互补特性处理双滑动窗内的信号，获取信号能量；通过设计符号定时函数对信号能量进行处理，使得在获取信号能量的同时定时测量函数达到最大值，从而得到准确的符号定时点。实验统计表明，在DD-O-OFDM系统下，经200km标准单模光纤（SSMF，standardsinglemodefiber），以1．5Gbit／s的速率传输后，本文算法在接收端能准确地捕获定时点，获得很高的捕获率，且比其它算法有更低的时偏均值及均方误差（MSE）。当接收功率低于-36dBm时，新算法仍然能够获得最小的定时估计均值和MSE，而其它算法性能明显下降。同时，在低于-40dBm的接收功率情况下，新算法仍能准确地捕获定时点，降低了同步算法对色散的敏感度。

英文摘要：

A novel symbol timing synchronization scheme for direct-detection optical orthogonal frequency division multiplexing （DD-O-OFDM） systems is proposed. Making use of the non-periodic auto-correla= tion complementary property of the Golay pair, the new algorithm processes the signals in the do＇able sliding window to capture signal energy. It processes the signal energy by designing symbol timing func- tion so that the timing function can reach the maximum to get the correct symbolic timing point while capturing signal energy. The performance＇ of the new algorithm is evaluated in terms of mean and mean- square error （MSE） in one experimental system with 1.5G bit/s DD-O-OFDM signal transmission over 200 km standard single mode fiber （SSMF）. The experimental results show that the new algorithm has smaller MSE than other algorithms and achieves higher timing estimation accuracy. When the received power is less than --36 dBm, the new algorithm can still obtain the smallest timing estimation mean and MSE,while the performance of other algorithms significantly decreases, so the timing precision of the new algorithm is the highest. Meanwhile,in the case of low power of -40 dBm,the new algorithm can still accurately capture the timing point, and reduce the sensitivity on dispersion of the system timing synchronization.