Integrating high altitude platforms (HAPs) and free space optical (FSO) communications is a promising solution to establish high data rate aerial links for the next generation wireless networks. However, practical limitations such as pointing errors and angle-of-arrival (AOA) fluctuations of the optical beam due to the orientation deviations of hovering HAPs make it challenging to implement HAP-based FSO links. For a ground-to-HAP FSO link, tractable, closed-form statistical channel models are derived in this article to simplify optimal design of such systems. The proposed models include the combined effects of atmospheric turbulence regimes (i.e., log-normal and gamma-gamma), pointing error induced geometrical loss, pointing jitter variance caused by beam wander, detector aperture size, beam-width, and AOA fluctuations of the received optical beam. The analytical expressions are corroborated by performing Monte--Carlo simulations. Furthermore, closed-form expressions for the outage probability of the considered link under different turbulence regimes are derived. Detailed analysis is carried out to optimize the transmitted laser beam and the field-of-view of the receiver for minimizing outage probability under different channel conditions. The obtained analytical results can be applied to finding the optimal parameter values and designing ground-to-HAP FSO links without resorting to time-consuming simulations.

中文翻译：

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地到 HAP 自由空间光通信的分析信道模型和链路设计优化

集成高空平台 (HAP) 和自由空间光 (FSO) 通信是为下一代无线网络建立高数据速率空中链路的有前途的解决方案。然而，由于悬停 HAP 的方向偏差导致的指向误差和光束到达角 (AOA) 波动等实际限制使得实施基于 HAP 的 FSO 链路具有挑战性。对于地面到 HAP FSO 链路，本文推导了易于处理的封闭形式统计信道模型，以简化此类系统的优化设计。提议的模型包括大气湍流状态（即对数正态和伽马伽马）的综合影响、指向误差引起的几何损失、由光束漂移引起的指向抖动方差、探测器孔径大小、波束宽度、和接收光束的 AOA 波动。分析表达式通过执行蒙特卡洛模拟得到证实。此外，推导出了不同湍流状态下所考虑链路的中断概率的闭式表达式。进行详细分析以优化发射的激光束和接收器的视场，以最大限度地减少不同信道条件下的中断概率。获得的分析结果可用于寻找最佳参数值和设计地面到 HAP FSO 链路，而无需求助于耗时的模拟。进行详细分析以优化发射的激光束和接收器的视场，以最大限度地减少不同信道条件下的中断概率。获得的分析结果可用于寻找最佳参数值和设计地面到 HAP FSO 链路，而无需求助于耗时的模拟。进行详细分析以优化发射的激光束和接收器的视场，以最大限度地减少不同信道条件下的中断概率。获得的分析结果可用于寻找最佳参数值和设计地面到 HAP FSO 链路，而无需求助于耗时的模拟。