Modelling and analysis of FSO ground-to-train communications for straight and curved tracks

In this work, a free space optical (FSO) link for the ground-to-train communications is proposed. Analytical analysis is carried out for the case of the straight track as well as curved rail tracks. We show that the transmitter divergence angle, the transmit power and the size of the concentration lens needs to increase for the curved section of the rail track compared to the straight track. We derive the analytical expression (11) for the received power level along the rail tracks based on the link geometry for the cases of straight and curved tracks. The received power variation is compared for two cases showing a similar dynamic range. In the worst case scenario when the radius of curvature is 120 m the transmit power at the base station (BS) needs to increase by over 2 dB when the concentration lens radius is increased by 5 times. Analyses also show that the received power increases with the radius of curvature. Finally, results are compared with the existing straight track model.