Free space optical (FSO) communication systems experience turbulence-induced fading. As a possible solution to mitigate the effects of fading, adaptive transmission that allows the adjustment of transmission parameters such as transmit power and modulation size can be used. Most of the existing works on adaptive FSO systems assume the presence of full channel state information (CSI) at the transmitter side. In practice, incomplete/outdated CSI may prevent the complete extraction of the theoretical gain expected from adaptive systems. In this letter, to avoid the difficulties associated with feedback, we propose a feedback-free adaptive modulation selection algorithm for FSO systems. We formulate the design as an optimization problem where average throughput is maximized by selecting the largest modulation order under the constraint that the required transmit power for a targeted bit error rate (BER) value does not exceed the maximum transmit power. We further present numerical results to confirm the superiority of the proposed adaptive algorithm.

中文翻译：

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FSO 系统的无反馈自适应调制选择算法


自由空间光学 (FSO) 通信系统会经历湍流引起的衰落。作为减轻衰落影响的可能解决方案，可以使用允许调整传输参数（例如传输功率和调制大小）的自适应传输。大多数自适应 FSO 系统的现有工作都假设发射机侧存在完整的信道状态信息 (CSI)。在实践中，不完整/过时的 CSI 可能会阻止自适应系统预期理论增益的完全提取。在这封信中，为了避免与反馈相关的困难，我们提出了一种用于 FSO 系统的无反馈自适应调制选择算法。我们将设计表述为一个优化问题，其中在目标误码率 (BER) 值所需的发射功率不超过最大发射功率的约束下，通过选择最大调制阶数来最大化平均吞吐量。我们进一步提出数值结果来证实所提出的自适应算法的优越性。