Mobility management for D2D communication combining radio frequency and visible light communications bands

Combination of radio frequency (RF) and visible light communication (VLC) bands for device-to-device (D2D) communication is seen as a promising way to both increase the system capacity and cope with an overcrowded RF bands. The main concern, however, is a proper mobility management and selection of the band that is beneficial at the moment. While the VLC usually provides a much higher throughput than RF, it is also very sensitive to a signal blockage and shadowing. Therefore, throughput as well as potential sudden drops in VLC channel quality should be considered in a design of handover between VLC and RF to avoid redundant handovers. In this paper, we propose an algorithm, tailored for D2D communication, deciding whether or not it is beneficial for a user equipment to switch from VLC to RF or vice versa. If handover to RF is not beneficial at the moment despite a drop in VLC channel quality, a dwell timer waits for a specific time if VLC channel recovers. We propose an optimization of the dwell timer according to estimated throughput in RF and VLC and delay due to handover. Simulations show that the proposed algorithm increases an average throughput when compared to existing state-of-the-art algorithms while number of handovers and average interruption are still very low.