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

Abstract

Free-Space-Optical (FSO) communication has the potential to not only deliver wireless communication links at optical-level speeds but also solve the wireless capacity problem that the traditional RF-based technologies are confronting. Despite its capacity advantages, FSO communication is prone to mobility. High directionality of FSO transceivers requires establishment and maintenance of line-of-sight (LOS) between them. Facilitating continuous alignment requirements has been a major concentration of mobile FSO research to date. We consider two autonomous mobile nodes, each with one FSO transceiver mounted on a movable head capable of rotating 360 degrees. We propose a novel scheme that deals with the problem of automatic detection, establishment and maintenance of LOS alignment between the two nodes with mechanical steering of the FSO transceivers. The proposed method shows that 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. We design protocols to maintain an FSO link between the mobiles satisfying a minimum received power or signal-to-noise ratio (SNR), and evaluate our designs for mobiles moving on straight lines or curves.