A Fast Handover Mechanism for Ground-to-Train Free-Space Optical Communication using Station ID Recognition by Dual-Port Camera

There are demands for high-speed and stable ground-to - train optical communication as a network environment for trains. The ex- isting ground-to-train optical communication system developed by the au- thors uses a camera and a QPD (Quadrant photo diode) to capture beacon light. The problem with the existing system is that it is impossible to iden- tify the ground station. In the system proposed in this paper, a beacon light modulated with the ID of the ground station is transmitted, and the ground station is identified by demodulating the image from the dual-port camera on the opposite side. In this paper, we developed an actual system and con- ducted experiments using a car on the road. The results showed that only one packet was lost with the ping command every 1 ms near handover. Although the communication device itself has a bandwidth of 100 Mbps, the throughput before and after the handover was about 94 Mbps, and only dropped to about 89.4 Mbps during the handover.