To enhance the error performance of satellite downlink optical wireless communication system, a hybrid modulation scheme called PPM-FSK-SIM is proposed in this study. It is based on the concept of pulse position modulation (PPM), M-ary frequency shift keying (MFSK) and subcarrier intensity modulation (SIM). The analytical bit error rate (BER) of the proposed hybrid scheme is derived, in the presence of atmospheric turbulence with avalanche photodiode (APD) detection by using Meijer-G, which stands out as a reliable and efficient analytical tool that replaces the time-consuming Monte-Carlo simulation method to target a desirable BER. It is analysed over additive white gaussian noise (AWGN), log-normal and gamma–gamma channel models for geostationary satellite to Earth (downlink) communication. As compared to PPM and minimum shift keying (MSK), PPM-MFSK-SIM gives better error rate performance. The scheme is power efficient making it a favourable modulation technique for satellite downlink communication.

中文翻译：

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基于PPM和FSK的FSO卫星下行混合调制方案误码性能分析

为了提高卫星下行光无线通信系统的误码性能，本研究提出了一种称为PPM-FSK-SIM的混合调制方案。它基于脉冲位置调制 (PPM)、多路频移键控 (MFSK) 和副载波强度调制 (SIM) 的概念。所提出的混合方案的分析误码率 (BER) 是在存在大气湍流和雪崩光电二极管 (APD) 检测的情况下通过使用 Meijer-G 推导出来的，Meijer-G 是一种可靠且高效的分析工具，可替代时间-消耗蒙特卡洛模拟方法以达到理想的 BER。对地球静止卫星到地球（下行链路）通信的附加高斯白噪声 (AWGN)、对数正态和伽马-伽马信道模型进行了分析。与 PPM 和最小移位键控 (MSK) 相比，PPM-MFSK-SIM 提供更好的错误率性能。该方案具有功率效率，使其成为卫星下行链路通信的有利调制技术。