Optimal UAV relay positions in multi-rate networks

The performance of ad hoc networks depends greatly on the network topology. Thus, deploying relays or controlling the position of network nodes may impact the performance. Unmanned Aerial Vehicles (UAVs) and other elevated platforms may improve the ground network performance when used as network relays, due to better Line-of-Sight (LoS) conditions. In addition, UAVs can easily move to better locations. This paper shows that positioning a UAV asymmetrically between two ground nodes could result in better communication services than a UAV placed at the center position between the ground nodes, given the use of stepwise adaptive modulation. The IEEE 802.11 WLAN standard, a popular Mobile Ad Hoc Network (MANET) protocol with multi-rate capabilities, is employed for quantification of the effect. Simulations results show that the network performance can be lower with a UAV at the center between two (clusters of) ground nodes for certain geometries. For networks actively supported by UAV relays, this effect must be taken into consideration when choosing the location and when estimating the available capacity, e.g., for routing or call admission.