The coherence distance (CD) is the spatial distance over which the channel does not change appreciably. It is a common and important wireless communication channel parameter. While adoption of this parameter in the realm of radio-frequency is well established, it is a less familiar concept in the realm of optical wireless communication (OWC), where it can be beneficial as a measure for spatial optical channel changes. In this Letter, the average CD is proposed as a metric to characterize indoor OWC channels and a method for its evaluation is outlined.

中文翻译：

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室内光无线通信信道中的相干距离

相干距离（CD）是信道不会明显改变的空间距离。它是一个常见且重要的无线通信信道参数。虽然已经很好地确定了在射频领域采用此参数，但是在光无线通信（OWC）领域中它并不是一个很熟悉的概念，它可以作为衡量空间光信道变化的一种措施。在这封信中，提出了将平均CD用作表征室内OWC频道的指标，并概述了其评估方法。