Uplink/Downlink Reciprocity in VLC Channels and Its Application to Rate Analysis of SLIPT Systems

In visible light communication (VLC) systems, the uplink and downlink channel gains depend on environmental geometry. This geometric nature induces a relationship between the uplink and downlink VLC channel gains. In this paper, the reciprocity relation between the uplink and downlink VLC channel gains are analyzed. It is shown that the reciprocity relationship can be accurately modeled as affine or polynomial. This reciprocity analysis can be a useful tool that enables several VLC system analysis and design. As an interesting application, using this channel reciprocity and model of the solar cell, the relationship between the downlink rate, harvested power and uplink rate are obtained for a solar cell based VLC-SLIPT system. This enables the formulation of the uplink-downlink rate region for a solar cell-based SLIPT system. The rate region gives the set of all simultaneously achievable rates in the uplink and downlink. The rate analysis, enabled by the reciprocity result, gives the trade-off between downlink and uplink rates that is essential in the system design of solar cell based SLIPT receivers.