GPS-Free Maintenance of A Free-Space-Optical Link Between Two Autonomous Mobiles

摘要

Free-Space-Optical (FSO) communication has the potential to provide optical-level wireless communication speeds. It can also help solve the wireless capacity problem experienced by the traditional RF-based technologies. Despite its capacity advantages, FSO communication is prone to mobility. Since the FSO transceivers are highly directional, they require establishment and maintenance of line-of-sight (LOS) between each other. We consider two autonomous mobile nodes, each with one FSO transceiver mounted on a movable head capable of rotating 360 degree. We propose a novel scheme that deals with the problem of automatic maintenance of LOS alignment between the two nodes with mechanical steering of the FSO transceivers. We design protocols to maintain an FSO link between the mobiles satisfying a minimum received power or signal-to-noise ratio (SNR). We also present a prototype implementation of such mobile node with FSO transceivers. The effectiveness of the alignment protocol is evaluated by analyzing the results obtained from both simulations and also experiments conducted using the prototype. The results show that, by using such mechanically steerable transceivers and a simple auto-alignment mechanism, it is possible to maintain optical wireless links in a mobile setting with nominal disruption.