空时网格码具有编码增益与频谱利用率高的特点, 针对强度调制直接检测(Intensity modulation/direct detection, IM/DD)方式, 提出了一种适合于大气激光通信的空时网格编码方案。该方案运用快速傅里叶逆变换(IFFT)的对称性以及加直流分量的方法解决了空时网格编码信号无法直接用于IM/DD链路传输MPSK信号的问题。之后, 通过蒙特卡洛方法分析了该方案在不同大气闪烁条件下的误码性能, 并对调制阶数和天线数对系统误码性能的影响进行了分析。结果表明: 所提方案能够有效抵御大气湍流所产生的闪烁效应, 其性能随天线数的增加而得到明显的改善, 并且在强湍流条件下表现出了更好的性能。

Space-time trellis code(STTC) has the advantage of high spectrum efficiency. A STTC coding scheme was proposed for M-PSK modulated intensity modulation/direct detection(IM/DD) atmospheric optical communication system. By using the proposed mothed, the problem that conventional STTC is unable to be directly applied to IM/DD link was eliminated by employing the IFFT symmetry and a direct-current (DC) component. The system BER performance in different atmospheric scintillation and modulation index was evaluated by Monte Carlo method. Simulation results show that the proposed scheme has the advantage of mitigating the scintillation effect caused by atmosphere turbulence, and the link BER performance improves with the increase of diversity gain particularly in strong turbulence channels.