Tethered UAV Deployment Strategies: The Coverage and Energy Efficiency Trade-Off

An unmanned aerial vehicle-mounted base station (UAV-BS), also known as an aerial base station (ABS), is a viable technology for the next 6G wireless networks due to its adaptability and affordability. Furthermore, the concept of tethered UAVs (TUAVs), can be used to circumvent the limited network operating time of UAV-BS networks. TUAVs are UAVs powered by a ground energy source via a tether that restrain their mobility while providing unlimited power. In this work, we propose a system where ABSs are deployed in user hotspots to offload the traffic and assist terrestrial base stations (TBSs). We will analyze three different scenarios and compare them in terms of coverage performance and energy efficiency. For a more realistic system, we offer a system model that considers the dynamic spatial distribution of users. First of all, we start by determining the optimal locations of TUAVs that minimize the average pathloss for each scenario. Next, using tools from stochastic geometry and an approach of dividing the space into concentric rings and slices to quantify the locations and orientations of ground stations (GSs), we analyze both coverage and energy performance for each scenario. We verify our findings using Monte-Carlo simulations and draw multiple useful insights. For instance, we show that deploying a TUAV with attachment and detachment capability for each pair of clusters outperforms deploying a normal TUAV for each cluster in terms of energy efficiency but not in terms of coverage performance.