Routing impact in highly dynamic mesh networks of RF and FSO links

Applications such as situational awareness are becoming more prevalent in highly dynamic tactical mesh networks and are placing high demand on existing RF network capacity. These applications require high aggregate data capacity but have some flexibility in packet by packet latency. Combined radio frequency and free space optical communication within a heavily scintillated atmospheric path behaves as an RF link augmented by an optical link. Such link scenarios are found in near-Earth paths within a network where high link availability is required but the aggregate data rate, although high, is flexible and has a dynamic range much wider than seen in traditional terrestrial networks. In a hybrid RF/FSO mobile network, a high data rate free space optical transmission provides a "link of opportunity" that supplements the RF, since atmospheric turbulence dominates link performance and drives the routing path selection criteria. This paper describes a characterization of a hybrid RF/FSO link that presents two paths of significantly different capacities to the router. Atmospheric turbulence is emulated on the FSO link in order to demonstrate the current challenges in using these links in tactical environments and we identify the optimizations required at the routing layer to take advantage of the very high aggregate mesh capacity in a network of combined RF and optical link paths.