Optimal Placement of FSO Links in Hybrid Wireless Optical Networks

Wireless mesh network addresses the last mile issue; however, RF-based technologies are still a bottleneck for todays' media-rich applications. In this paper, we propose enhancing the capacity of an existing wireless mesh backhaul using free-space optical links. Such a hybrid RF/FSO network is capable of multiplying the available bandwidth for each subscriber if the FSO transceivers are placed at strategically located nodes. Adopting a TDMA- based framework, we formulate a problem for the optimal placement of FSO transceivers and RF link activation schedules which maximize the network capacity. An integer-linear program (ILP) is developed to obtain an optimal solution. Due to the complexity of this ILP, we also propose a relaxation which yields an upper bound on the network capacity in such an architecture, and develop a probabilistic heuristic that approaches this capacity. We show by simulations that our heuristic achieves a high fraction of the network capacity upper bound, and it can be implemented efficiently.