Abstract
The growing deployment and advanced development of high-speed train systems calls for provisioning of broadband Internet services, which cannot be readily provided by the existing radio frequency technology. Thus, an alternative technology, namely, free space optics (FSO), has been proposed to overcome the bandwidth bottleneck problem. However, as each FSO base station (BS) only covers a short length along the track, a large number of BSs are required to realize the seamless coverage, thus incurring high capital expenditures to the railway operator as well as frequent handover processes, which may degrade the system performance. In order to solve this problem, we propose a dual transceivers scheme in a ground-to-train communications system. Since two transceivers of a BS can point to different directions, laser beams of the BS can be transmitted forwardly and backwardly such that the total coverage length of each BS is remarkably extended. Furthermore, the two coverage areas of a BS's transceivers are not contiguous along the track, thus forming a blackout area between them. In this case, two transceivers of a train, which are deployed at the front and back of a train, respectively, can cooperate to maintain continuous ground-to-train FSO communications. Therefore, the number of the BSs is reduced, and the impact of frequent handovers is alleviated. The performance of the proposed scheme is demonstrated via extensive simulations.