Performance Analysis and Enhancement of Unmanned Aerial Vehicle Based Free Space Optical Communication System

Abstract

Unmanned aerial vehicles (UAVs) are attractive solutions for current and future wireless communication systems. Radio-frequency (RF)-based UAV growth is projected to be USD 49.0 billion by 2026, and UAVs inherent nature provides a wide range of applications. RF-based UAVs have sig- nificant limitations, such as higher data rate, limited RF spectrum, fron- thaul/backhaul link, interference, security and latency requirement, inter UAV coordination. UAV-based Free-space optics (FSO) is the alterna- tive solution for such needs. High-altitude platform (HAP)/UAVs play a critical role in connecting terrestrial to satellite networks via FSO commu- nication links to provide services such as 5G, 5G+ networks were hard to reach areas. HAPs/UAVs act as a relay, base stations, and high capacity backhaul/fronthaul links for civilian navy, military, and disaster manage- ment applications. Due to alignment issues developing a channel model for inter UAV based FSO communication is a difficult task. The various alignment strategies and channel models that exist in the literature have been studied, and they are complex. In First work, we proposed and deduced a simple channel model using Meijer’s G functions for inter UAV communication. The derived analytical channel model results are verified with Monte-Carlo simulations. We used heterodyne detection (HD) in FSO-based inter-UAV communication for the first time. The proposed systems outage and average bit error rate (BER) performance are evaluated, and the results are compared to existing Intensity modulation direct detection (IM/DD) systems. The first proposed system has the disadvantage of not being suitable for long-range applications. Inter UAV-based FSO communication systems distance is another performance-limiting factor as the distance increases the systems performance worst, as shown in the literature. We proposed polarization shift keying modulation (POLSK) modulation for long-range inter UAV-based FSO communication systems in our second work. The performance metrics are derived and the results are analysed under dif- ferent weather conditions. Results indicated that significant performance improvement under POLSK modulation when compared with the exist- v ing On-off-keying (OOK) modulation scheme. We showed optimal values selection under different weather conditions for inter UAVs. The inherent nature of HAPs provides larger coverage areas with bet- ter Line-of-sight (LOS), rapid development, and low maintenance costs. HAP is mainly used to connect the satellite to the ground station via a high-capacity optical backhaul link. Such a high-capacity HAP-based FSO communication link under hovering HAP fluctuations performance analy- sis is challenging. We addressed this challenge in the third work. Derived the Ground-to-HAP, HAP-to-Ground channel model under hovering state fluctuations. We improved the Ground-to-HAP-based FSO links perfor- mance using coding techniques. The growth of internet of things and 5G networks required convergent systems like, RF, millimetre wave, FSO and Underwater wireless optical communication (UWOC) etc. UWOC links are mainly focused on the ap- plications of underwater ranging and imaging. The drawback of UWOC systems is poor BER performance under absorption and scattering, link misalignment, random movement of the sea surface, and complex envi- ronment. In the Fourth work, we proposed the HAP-UWOC communi- cation systems under hovering fluctuations for HAP backhaul to under- water applications. We evaluated the BER performance of HAP, UWOC, and HAP-UWOC links. Evaluated the end-to-end performance of HAP- UWOC under the clear ocean, coastal ocean, Turbid harbor, and HAP hovering fluctuations are considered.