Error performance of hybrid subcarrier intensity modulation (hybrid-SIM) in optical free-space satellite downlink has been studied in this work. Bit error rate (BER) is improved by aperture averaging and spatial receiver diversity and it is found out be effective in strong turbulence regime. Subsequently, the reduction in scintillation index has been investigated by implementing a single large receiver and an array of point receivers of length with the same effective aperture area. Moreover, the BER at different turbulence conditions is compared with minimum shift keying and multiple levels of pulse position modulation pertaining to aperture averaging. Upon analysing the single input multiple outputs (SIMO) system, the desired response is obtained above a certain threshold in average received irradiance. At different zenith angles and turbulence strengths for , the threshold is 4.59 and 3.35 dB, respectively, and it rises by 13.6 and 26.43 dB when is increased to 9. This constraint can be exploited to optimise the number of receivers concerning system requirement and availability. Further, the pointing error effects are also investigated for SISO and SIMO systems, which takes into account both atmospheric turbulence and misalignment induced fading.

中文翻译：

---

具有孔径平均和接收器分集的用于光无线下行链路通信的混合SIM卡的性能增强

在这项工作中，已经研究了在光自由空间卫星下行链路中混合子载波强度调制（Hybrid-SIM）的误码性能。通过孔径平均和空间接收器分集提高了误码率（BER），发现误码率在强湍流条件下是有效的。随后，通过实现单个大型接收器和长度为点的接收器阵列，研究了闪烁指数的降低具有相同的有效光圈面积。此外，将在不同湍流条件下的误码率与最小移位键控以及与孔径平均有关的多级脉冲位置调制进行了比较。通过分析单输入多输出（SIMO）系统，可以在平均接收辐照度的某个阈值以上获得所需的响应。在不同的天顶角度和湍流强度下 ，该阈值分别为4.59和3.35 dB，并且在出现以下情况时分别增加13.6和26.43 dB 增加到9。可以利用此约束来优化与系统需求和可用性有关的接收器数量。此外，还针对SISO和SIMO系统研究了指向误差的影响，同时考虑了大气湍流和未对准引起的衰落。