Coherence Time Evaluation in Indoor Optical Wireless Communication Channels

Abstract

The coherence time is the time over which the channel-gain-values correlation coefficient drops below a predefined threshold. The coherence time is typically used to quantify the pace of appreciable channel changes and is important, for example, for determining handoff and resource allocation time constraints. The goal of this work is to experimentally measure the coherence time of indoor optical wireless communication (OWC) channels under various mobile scenarios. The amount of movement was quantified by mobile sensor measurements. The experiments show that it is reasonable to assume that the channel varies slowly for a time period of ~100 milliseconds for most mobile scenarios.

Keywords

• optical wireless communication
• coherence time
• optical wireless channel
• autocovariance function (ACF)
• nine degrees of freedom (9DoF)