Optimal placement of FSO relays for network disaster recovery

Free Space Optics (FSO) relays can be used to recover a network which is partially disconnected due to natural disasters or terrorist attacks. Rapid and efficient recovery can be achieved thanks to FSO technology being wireless and providing high bandwidth. However, placement of such relays is a challenging problem as FSO links greatly depend on weather conditions. In this paper, we find the minimum number of transceivers and their optimal placement which guarantees the recovery of a certain fraction of network capacity in the worst weather conditions and maximizes the throughput in the best weather conditions through transceiver reconfiguration. The problem is formulated as an integer linear program (ILP) which takes the link availability prediction as an input and guarantees fairness to all existing traffic flows. To avoid the complexity of the ILP, an efficient probabilistic heuristic that computes the placement of FSO transceivers is proposed. We show through extensive simulations that the heuristic performs within 12% of the optimal performance.