Executive Summary : | As fifth-generation (5G) wireless technologies are currently being rolled out worldwide, it is expected that sixth-generation (6G) wireless networks with enhanced capabilities compared to 5G networks will be implemented between 2027 and 2030. Further, it is also expected that 6G will include ubiquitous mobile ultra-broadband services everywhere including new environments such as sky, sea, etc. compared to the enhanced mobile broadband services in 5G. Free space optics (FSO) communication, which is the term used for optical wireless communication in outdoor scenario, is cost effective, license-free, and offers higher data rates of the order of gigabits per second (GBPS) as compared to radio frequency (RF) communication. Thus, FSO can support seamless ubiquitous high-speed broadband connectivity, which is a significant requirement for 6G backhaul networks and satellite communication (SATCOM). Aerial platforms such as unmanned-aerial-vehicles (UAVs), high-altitude platform station (HAPS), etc. have been considered to play a promising role in 6G communication, where they will be deployed either as a mobile relay station or as a flying aerial base station due to its advantages such as faster deployment than terrestrial relay nodes, medium operational costs, environmental friendliness, etc. In 6G communication, it is also envisioned that the data transmission will be over space-air-ground integrated networks (SAGIN), which is the integration of satellite system, ground or terrestrial system, and aerial networks, to provide broadband global mobile connectivity. Thus, our main aim in this project is to propose novel system models utilizing aerial platforms and FSO communication for terrestrial networks and SAGIN scenarios, which are expected to be featured in 6G communications. Despite various advantages, the aerial-platform-based FSO communication is undermined by several factors such as atmospheric turbulence, pointing errors, atmospheric attenuation, and angle-of-arrival fluctuations due to orientation deviation of hovering aerial platforms. To improve the system performance in terms of capacity, reliability, and energy efficiency, advanced wireless communication techniques such as energy harvesting, multi-hop UAV-based FSO communication, multiple-HAPS-based SAGIN, reconfigurable intelligent surface (RIS)-assisted FSO communication, hybrid FSO/millimeter wave communication, optical index modulation, non-orthogonal multiple access (NOMA), etc. will be utilized. Further, comprehensive end-to-end system performance of the proposed system models considering the above-mentioned state-of-the-art techniques will be investigated in terms of performance metrics such as outage probability, average symbol error probability, coverage probability, ergodic capacity, outage capacity, etc. Finally, RIS-assisted UAV-based FSO communication testbed will be designed and developed in a lab environment to validate analytical and simulation results. |