自由空间光通信中相干OFDM系统性能分析

结合正交频分复用（OFDM）技术和相干探测的优势，研究了相干OFDM自由空间光通信（FSO）系统的误码性能，考虑了OFDM映射方式以及映射阶数对系统误码性能的影响。在Gamma-Gamma大气湍流信道下，分别从平均信噪比和所需平均接受光功率的角度考虑了系统在弱、中和强湍流三种情况下的误码性能。在此基础上，推导了系统误符号率的闭合表达式。仿真结果表明，相干探测下OFDM FSO系统可以较好地克服大气湍流效应，在弱、中湍流情况下，QAM映射方式下系统的误码性能明显优于PSK方式，在强湍流下这种优势不明显，此外随着映射阶数的增加，系统误符号率增加，因此在实际应用中可以通过降低映射阶数来提高系统误码性能。

Performance analysis of coherent OFDM system in free space optical communication

Combining the advantages of OFDM technology with the coherent detection, the bit error rate(BER) performance of coherent OFDM FSO system was studied, and the influence of OFDM mapping mode and mapping order on the symbol error of the system was taken into account. In Gamma-Gamma atmospheric turbulence channel model, the bit error performance of three cases of weak, moderate and strong turbulence were taken into consideration separately from the perspective of the average signal-to-noise ratio and the required average received optical power. On this basis, the closed form expression of the symbol error rate was deduced. Simulation results show that the coherent detection OFDM FSO system can better overcome the effects of atmospheric turbulence, in weak and moderate turbulence, the system BER performance with QAM mapping mode is obviously better than that of PSK mapping mode, however, under the strong turbulence the advantage is not very obvious. In addition, with the increase of mapping order, system symbol error rate increases, so in practice it can improve the system BER performance by reducing the number of mapping order.