All-Optical UAV-Based Triple-Hop FSO-FSO-VLC Cooperative System for High-Speed Broadband Internet Access in High-Speed Trains

In this paper, we proposed an unmanned aerial vehicle (UAV) based all optical triple hop mixed free space optical-free space optical-visible light communication (FSO-FSO-VLC) system for broadband internet access in high-speed train applications. The system consists of triple hops from gateway to the UAV, UAV to train and train to the end user. Two decode and forward relays are mounted on the UAV and train respectively to transmit the data between the gateway to the end-users. The first hop between gateway to UAV consist of FSO link which follows M-distribution. The second hop between the UAV to train consists of FSO link and is modelled using Gamma-Gamma distribution which takes into account both atmospheric turbulence and pointing errors due to position/orientation deviation. The third hop between the train and end user is connected using VLC link and it is mathematically modelled using Lambertian emission distribution. The relays map the incoming signal on the FSO links and send it down to the user inside the train via the VLC downlink. We derived the closed form expressions for average bit error rate and outage probability of the proposed system. This paper investigates the effects of atmospheric turbulence, field of view, beam divergence angle, displacement deviation variance, optical concentrator gain, number of access point, and modulation schemes on system performance. First time, we proposed all-optical system which offers high data rate and low transmission delay.