多输入多输出(MIMO)技术可以在不额外增加频谱资源和发射功率的条件下成倍提高通信系统的信道容量, 但子信道间存在的空间相关性会影响光MIMO无线通信系统(OWC)的性能。本文研究了对数衰落信道中空间相关性对光MIMO系统误码率的影响。针对脉冲位置调制(PPM)方式, 采用指数相关模型推导出了光MIMO通信系统在不同相关机制下的对数振幅衰落系数矩阵和最大似然检测准则。然后, 采用Wilkinson近似方法推导出了该条件下光 MIMO系统误码率的上界。最后, 利用仿真实验进一步分析了空间相关性对OWC MIMO系统误码率的影响。结果表明: 空间相关性的存在使得OWC MIMO系统的性能恶化, 且随着收发天线数量的增加, 空间相关性会导致系统误码率恶化加剧。因此在实际工程应用中要合理放置天线, 尽量减小天线之间的相关性, 以便更好地发挥MIMO系统的优势。

Multiple Input Multiple Output (MIMO) systems can improve the channel capability of an Optical Wireless Communication(OWC) system without adding extra frequency resources and emitting powers, but the space correlation between the channels will impact the system performance. This paper researches the effects of space correlation on the Bit Error Rate (BER) of an optical MIMO system in log-normal fading channel. In view of the Pulse Position Modulation (PPM), the log-amplitude fading matrix in different correlation mechanisms and maximum likelihood detection rule were derived by using an exponential correlation model in the log-normal fading channel. On the basis of this, the upper bound of the BER of correlated OWC MIMO system was deduced by adopting Wilkinson method. Finally, the impact of space correlation on BER of the OWC MIMO system was analyzed further. The results show that space correlation deteriorates the performance of OWC MIMO system and the BER of the system will be worsen by the space correction with the increase of the number of the antenna. It suggests that antennas should be placed reasonably to reduce the space correction between the antennas, so to better play the advantages of MIMO systems.