Group-based concurrent transmissions for spatial efficiency in IEEE 802.15.7 visible light communications

This paper presents a group-based concurrent transmission (GCT) scheme for visible light communications (VLCs), which aims to improve the spatial efficiency of IEEE 802.15.7-based VLC personal area networks (VPANs). To this end, the GCT combines the VLC devices that interfere with each other into a group taking into account the directionality of the light sources, and thus allows the concurrent transmissions of device groups. Then, it differentiates the BE value of each device group according to the number of VLC devices in the group, to prevent unnecessary backoff delay and collision. The GCT has two main operations: (1) VLC device grouping and (2) concurrent transmission scheduling. In the former, each device conducts neighbor discovery to create VLC device table (VDT) entries, through which the central controller builds groups considering the interference between neighbors. In the latter, the BE decision procedure is performed, in which the central controller allocates the different BE value to each group in accordance with the number of devices belonging to the group. To evaluate the performance of GCT, we developed the analytical model using the discrete-time Markov chain. The numerical results show that the GCT achieves a better network performance than the IEEE 802.15.7 standard.