中文摘要：

多输入多输出（MIMO）技术是消除大气闪烁对空间光通信的影响和降低误码率（sER）的有效手段之一。针对2×2空间光通信系统，将Alamouti空时码与跳时超宽带技术（TH—UWB）结合，提出一种适合脉冲位置调制（PPM）的循环空时编码（RSTC）方法，推导了等增益合并（EGC）最大似然检测（MLD）和相关矩阵检测（CMD）的两种解码算法，最后分析了系统误码性能。在弱湍流和准静态衰落信道条件下仿真，结果表明，无论是在信道信息（CSI）已知还是未知情况下，编码2×2系统的误码率高于未编码的。该编码方法获得了空间和时间分集，相关矩阵检测法取得相似于信道最大比值合并（MRC）的效果，但随信道间相关性增加其误码性能下降明显。

英文摘要：

The multiple-input-multiple-output （MIMO） technique is one of the effective means to mitigate the effects of atmospheric scintillation and reduce the symbol error rate （SER） for free-space optical communications. Considering the combinatin of Alamouti space-time code and time topping ultra-wide band （TH-UWB） communications, a novel repetition space-time codes （RSTC） method for 2×2 free-space optical communications with pulse position modulation （PPM） is developed. In particular, two decoding methods of equal gain combining （EGC） maximum likelihood detection （MLD） and correlation matrix detection （CMD） are derived. When a quasi-static fading and weak turbulence channel model is considered, simulation is conducted. Simulation results show that whether the channel state information （CSI） is known or unknown, the coding system demonstrates more significant performance of the SER than the uncoding. In other words, transmitting diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from the different antennas. CMD has almost the same effect of signal combing with maximal ratio combining （MRC）. However, when the channel correlation increases, SER performance of the coding 2×2 system degrades significantly.