Link Allocation, Routing and Scheduling of FSO Augmented RF Wireless Mesh Networks

Wireless Mesh Networks (WMNs) are designed to provide broadband wireless services; however, capacities of WMNs are fundamentally limited in bandwidth because of the scarcity of RF spectral resources. A solution is to design a WMN using multiple wireless technologies. Since the optical spectrum remains unlicensed and under-utilized, we propose to augment RF WMNs with free space optical (FSO) systems. FSO links do not interfere with RF links and have higher capacity than RF links. In this paper, we study the throughput improvement of FSO-augmented RF WMNs. We address two questions. First, given a fixed number of FSO links, where should we install them to achieve the maximum improvement of network throughput for given traffic demands? Second, how do we route and schedule the flows in the hybrid FSO/RF network to achieve this throughput? We jointly formulate the above problems as one mixed integer linear programming problem. The results show that the throughput of the network increases dramatically by properly allocating FSO links. We also provide a computationally efficient algorithm to evaluate upper and lower bounds on the throughput of this hybrid FSO/RF network. The network administrator can use these bounds to determine the tradeoff between the number of FSO links (which are expensive) and the throughput improvement.