A Point-to-Multi-Point Tracking System for FSO Communication

Free space optics (FSO) is considered primarily for establishing point-to-point (PtP). However, due to the increasing demand for mobile platforms and mechanisms to establish point-to-multipoint (PtM) connections, this research proposes and implements a novel PtM tracking mechanism for FSO communication. The alignment mechanism consists of two tracking systems, i.e., coarse tracking and fine-tuning. The coarse tracking is responsible to locate FSO transceivers placed at different positions by using magnetometer sensors connected to the cloud. On the other hand, the fine-tuning mechanism overcomes high-frequency amplitude oscillation or jitter with a displacement range of 8 cm. The link is continuously monitored and if the link is lost or not established after a pre-determined time, then the reference line-of-sight (LoS) angle is updated in the cloud to provide an alternate connection. The stability of the closed-loop system is analyzed in terms of root locus and step response. The proposed PtM system is experimentally validated with FSO terminals located at different locations and distances over indoor and outdoor environments. The proposed method achieved an alignment time of less than 5 s for ten degrees of misalignment.