Capacity scaling in free-space-optical mobile ad hoc networks

Wireless networking has conventionally been realized via radio-frequency-based communication technologies. Free-space-optical (FSO) communication with an innovative multi-element node design leverages spatially-diverse optical wireless links; making it a viable solution to the well-known diminishing per-node throughput problem in large-scale RF networks. Although it has the advantage of high-speed modulation, maintenance of line-of-sight between two FSO transceivers during a transmission is a challenge since FSO transmitters are highly directional. In this paper, we present our simulation efforts to make high-level assessments on throughput characteristics of FSO-MANETs while considering properties of FSO propagation and existence of multiple directional transceivers. We identify the intermittent connectivity problem that is caused by the relative mobility of nodes with multiple directional transceivers. We propose two cross-layer buffering schemes to remedy this problem and present their performance results. We conclude that sophisticated buffering mechanisms are required to properly buffer a packet during the misalignment period of two communicating nodes to avoid negative effects of this intermittency on the transport layer.