空时分组码虽然获得了满分集增益，但因不能提供编码增益而使系统性能受到限制。首先介绍了光MIMO系统的信道模型；其次针对Q-PPM(Q>2)调制方式，完成了对已有空时分组码的改进，并和RS 码相级联而提出了一种级联空时分组编码方案。在此基础上分析了该方法的误码性能。最后，利用仿真实验进一步验证了该方法的可行性，并和级联重复码的性能进行了对比。结果表明：在大气激光通信中，随着信噪比的增加，级联空时分组码获得了较高的编码增益，有效抵御了大气湍流效应。

Space-time Block Code (STBC) can achieve full diversity gain, but it can not provide code gain. So the system error rate capability will be restricted. In this paper, the optical Multiple Input Multiple Output (MIMO) system channel model was introduced at first. Then, for Q-PPM (Q>2) modulation, the existing STBC is amended. Moreover, by concatenating RS code, a concatenated STBC is proposed and its upper bound of error rate is analyzed. At last, the feasibility of this method is proved by the simulation experiment result. Compared the result with repetition code that concatenated RS code, it is shown that in atmosphere laser communication, the concatenated STBC can provide higher code gain.