中文摘要：

分析了直接检测光OFDM（DDO-OFDM）传输系统中由数模转换器和光纤链路中的光纤色散所致的OFDM信号高频衰减现象，以及经光纤传输后在光电检测时存在的子载波问互拍干扰现象。提出使用级联变系数训练序列和预增强结构的光OFDM（O-OFDM）信号来降低传输系统所受到的影响。理论分析和实验验证表明，级联变系数训练序列和预增强结构的基带OFDM信号在DDO—OFDM传输系统中，接收灵敏度比常规的交叉型训练序列结构的OFDM信号要高。说明基于级联变系数训练序列和预增强结构的O-OFDM信号的传输性能在抵抗子载波间互拍干扰（SSMI）和频率选择性衰减（FF）方面要优于常规的交叉型训练序列结构的O-OFDM信号。

英文摘要：

Frequency selective fading （FF） caused by digital to analog converter and optical fiber dispersion in optical fiber link was analysed, and signal-signal mixing interference （SSMI） when the orthogonal frequency division multiplex- ing （OFDM） signal was detected by PIN after transmitting over the fiber in direct-detection optical OFDM system. The cascaded variable coefficient training sequences and pre-emphasized configuration of O-OFDM signal were proposed to decrease the influence of the SSMI and FF. The theoretical analysis and experimental results show that the receiving sen- sitivity of the cascaded variable coefficient training sequences and pre-emphasized configuration of OFDM signal is higher than the interleaved configuration of training sequence of OFDM signal in DDO-OFDM system. It is demon- strated that the fiber transmission performance of the cascaded variable coefficient training sequences and pre-emphasized configuration of O-OFDM signal is better than the interleaved configuration of training sequence of OFDM signal in robust tolerance against SSMI and FF.