Randomized 3D Neighbor Discovery with Mechanically Steered FSO Transceivers

Free-space optical (FSO) communication has recently found credible mobile applications between high-altitude platforms (HAPs) and satellites. Success of these applications rely heavily on line-of-sight (LOS) beam discovery and alignment. Unlike millimeter-wave or Terahertz systems using antenna arrays with large electronic beam-steering capability, FSO systems utilize mechanical steering to scan angles more than a few degrees. In this paper, we design an LOS link discovery method for mechanically steered FSO transceivers attached to flying nodes. We assume that the nodes know each others’ locations with an error significantly larger than the footprint of the FSO beam. The FSO transceivers are full-duplex and do not have access to out-of-band radio channels. We design an all-optical neighbor discovery and beam alignment method that randomly searches the space where the other node may be. Our design ensures uniform search of the search space to maximize the detection probability of the other node. 3D simulations show that our method significantly improves the beam discovery time in comparison to the baseline method of scanning the space linearly.