This work is focused on the modeling and performance investigation of a 2 × 20 Gbit/s–40 GHz hybrid mode division multiplexing–orthogonal frequency division multiplexing-based radio over free space optics (RoFSO) transmission system under the influence of different weather conditions. The performance of the proposed system has been compared for 4-quadrature amplitude modulation (QAM), differential quadrature phase-shift keying, 16-QAM, and 32-QAM modulation schemes using error vector magnitude, optical signal-to-noise ratio requirement, and maximum link reach as the performance metrics. The results show that 4-QAM scheme demonstrates the best performance. The proposed RoFSO transmission system incorporating 4-QAM modulation demonstrates a successful transmission of 2 × 20 Gbit/s–40 GHz information over 104 km link range under clear weather conditions. Also, the maximum link range using the proposed system is reported as 4.52 km under light fog, 2.78 km under moderate fog, and 2.11 km under heavy fog conditions. Further, the performance of the proposed system has been compared with the previously reported literature which shows that the proposed system has a better figure of merit (information rate × transmission distance). The presented work can be used to implement a spectrum efficient, high-speed, long-haul information transmission system for future wireless networks.

中文翻译：

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FSO传输系统中基于2×20 Gbit / s–40 GHz混合MDM–OFDM的无线电中M-QAM和DQPSK调制方案的性能比较

这项工作的重点是在 不同天气条件的影响下，对基于2 × 20 Gbit / s–40 GHz混合模式划分复用–正交频分复用的基于自由空间光学（RoFSO）的无线电传输系统进行建模和性能研究 。已针对使用误差矢量幅度，光信噪比要求，四正交幅度调制（QAM），差分正交相移键控，16-QAM和32-QAM调制方案的提议系统的性能进行了比较，和最大链接覆盖率作为性能指标。结果表明4-QAM方案表现出最佳性能。拟议的结合了4-QAM调制的RoFSO传输系统证明了2 ×的成功传输  在晴朗天气下，在104 km的链路范围内提供20 Gbit / s–40 GHz的信息。此外，据报道，使用建议的系统的最大链路范围在轻雾下为4.52 km，在中雾下为2.78 km，在大雾条件下为2.11 km。此外，将所提出的系统的性能与先前报道的文献进行比较，这表明所提出的系统具有更好的品质因数（信息率 × 传输距离）。提出的工作可用于为未来的无线网络实现频谱高效，高速，长途信息传输系统。