Two-stage access point selection for hybrid VLC and RF networks

This work studies the issue of access point selection (APS) in a hybrid wireless network accommodating visible light communication (VLC) and radio-frequency (RF) technologies. A hybrid network constructs multiple layers of coverage, and thus a user possibly acquires a high level of receiving signal strength (RSS) from more than one access point (AP). This fact undermines the effectiveness of conventional RSS-based APS methods. Another challenging factor is the dissimilarity between heterogeneous APs in terms of coverage area and capacity. In general, RF offers larger coverage area but lower capacity than VLC, and therefore the RF system is susceptible to overload. Although the issue of APS can be formulated as an optimisation problem, this approach requires a prohibitive amount of processing power. In this paper a two-stage APS method is proposed on the basis of fuzzy logic, with very low computational complexity. The new method first determines the users that should be connected to the RF system, and then assigns the remaining users as if in a stand-alone VLC network. Results show that when achieving the same amount of throughput, the proposed method can support up to 25% and 56% more users than the load balancing (LB) and signal strength strategy (SSS) methods, respectively.