Protocol Design and Capacity Analysis in Hybrid Network of Visible Light Communication and OFDMA Systems

Visible light communication (VLC) uses a vast unregulated and free light spectrum. It is considered to be a solution for overcoming the crowded radio spectrum for wireless communication systems. However, duplex communication, user mobility, and handover mechanisms are becoming challenging tasks in a VLC system. This paper proposes a hybrid network model of VLC and orthogonal frequency-division multiplexing access (OFDMA) in which the VLC channel is only used for downlink transmission, whereas OFDMA channels are served for uplinks in any situation or for downlinks only without VLC hotspots coverage. A novel protocol is proposed combined with access, horizontal, and vertical handover mechanisms for mobile terminal (MT) to resolve user mobility among different hotspots and OFDMA system. A new VLC network scheme and its frame format are presented to deal with the multiuser access problems in every hotspot. In addition, a new metric ρ is defined to evaluate the capacity of this hybrid network as the spatial density of interarrival time of MT requests in s^-1m^-2 under the assumption of the homogenous Poisson point process (HPPP) distribution of MTs. Analytical and simulation results show improvements in capacity performance of the hybrid, when compared to OFDMA system.