a iKSP Journal of Computer Science and Engineering http://iksp.org/journals/index.php/ijcse/index iKSP Publisher Opportunistic Cooperative Relaying Protocol for UAV-assisted Flying Adhoc Network Muhammad Nauman Bashir* 1 , 1 Kamaludin Mohamad Yusof 1 1 School of Electrical Engineering, Faculty of Engineering, University Technology Malaysia, Johor, Malaysia _______________________________________________________________________________________________ Abstract - A tremendous rise in the use of Unmanned Aerial Vehicles (UAVs) in wireless communication is recently observed. Due to the useful features of UAVs, a new era of over-the-head wireless communication is finding its space at a rapid pace. A range of civilian and military applications is being tested using such UAV-assisted Flying Ad-hoc Networks. In such networks, the quality of communication is usually affected due to fading on channels and limited resources of the UAVs. In this work, we study the outage performance of dual-hop network over Rayleigh fading air-to- ground channels between source UAV and destination Ground Control Station and a group of intermediate UAV aerial relays. We focus on spatial diversity using cooperative relaying through relaying UAVs working in a cooperative manner to support the communication using maximum ratio combining at the destination. The best relay may be selected based on channel state information in terms of signal-to-noise ratio to make the system resource efficient. UAVs are assumed to work in Amplify and Forward mode in Half Duplexed downlink communication scenarios while deriving the closed- form expression for the outage probability. Numerical results are validated using Monte Carlo Simulations to study the impact of various system parameters on performance. The results of proposed non-buffer aided scheme is compared with compulsory direct-only communication. The impact of number of intermediate relays on dual hop links, symmetric and asymmetric channels is studied. The results are compared by changing the data rate and SNR of the links. The results show that cooperative relaying decreases the outage probability. More relays in cooperation, improve the system performance but at the cost of the network increased resources. Keywords: Flying Ad-hoc Network, Dual-hop, System Outage Probability, Spatial Diversity, Cooperative Relaying, Relay Selection _______________________________________________________________________________________________ INTRODUCTION The Unmanned Aerial Vehicles (UAVs) assisted Flying Ad-hoc Networks (FANETs) are becoming popular in a range of applications like remote sensing, search and rescue operations, traffic monitoring, disaster management, wildlife surveillance, agriculture and communication network expansions, etc. FANETs can disseminate target area observations through multi-hop relayed communication however; these applications demand quality and reliability in operation. The small UAVs in such networks can provide Line of Sight (LoS) communication up to a range of 75 m. Single cluster FANET has its own limitations while Multi-Cluster FANET provides better efficient network management at a reduced cost of communication. Due to typical issues of UAVs, ensuring the quality of service (QoS) in such networks is challenging. Usually UAVs in FANET move at higher speeds of 30-460 km/hr. (İlker Bekmezci, 2013) due to which the network topology is intermittent having fluctuating channel conditions. 1 *Corresponding author: Email: bashir-1977@graduate.utm.my (M.N. Bashir), Email: kamalmy@fke.utm.my (K.M. Yusof) iKSP Journal of Computer Science and Engineering (2022) 2(1): 20-26 This work is licensed under a Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.