Unmanned Aerial Vehicles (UAVs) can be used to provide wireless connectivity to support the existing infrastructure in hot-spots or replace it in cases of destruction. UAV-enabled wireless provides several advantages in network performance due to drone small cells (DSCs) mobility despite the limited onboard energy. However, the problem of resource allocation has added complexity. In this paper, we propose an energy-efficient user clustering mechanism based on Gaussian mixture models (GMM) using a modified Expected-Maximization (EM) algorithm. The algorithm is intended to provide the initial user clustering and drone deployment upon which additional mechanisms can be employed to further enhance the system performance. The proposed algorithm improves the energy efficiency of the system by 25% and link reliability by 18.3% compared to other baseline methods.
I. INTRODUCTIONDrone small cells (DSCs) have gained popularity in recent years as a solution to wireless communication problems such as lack of fixed infrastructure (e.g. due to natural disasters) or the need for temporal capacity increase (e.g. to manage traffic in a mass-event). If properly deployed, and despite its inherent limitations, UAV-enabled wireless can leverage the performance of the network due to increased probability for line-of-sight (LOS) connectivity and reduced total path loss. Furthermore, due to their mobility, the location of the BS can adapt to the changes in ground user distribution to improve the total throughput of the system. DSCs can also be a cost-effective substitute for building expensive cellular towers and infrastructure where the need for such infrastructure is limited in terms of time or capacity [1], or be deployed along with existing infrastructure in heterogeneous cellular networks [2].Nonetheless, utilizing UAVs for serving ground users in a given area has its limitations. Limited onboard energy restricts the deployment duration and transmit power thereby limiting the communication range. Furthermore, in the case of multiple DSCs, severe co-channel interference can substantially degrade users' link qualities [3]. Therefore, the problem of 3D deployment and user allocation is a complex one when taking into consideration factors such as power minimization and interference mitigation. DSCs locations should minimize the path loss and maximize signal-to-interference-plus-noise-ratio (SINR) along with serving the highest possible number of users. Additionally, DSCs should be aware of each other to avoid inter-UAV collisions [1].The topic of DSCs deployment optimization gained a lot of focus in recent years [4][5][6][7][8][9][10]. The problem is commonly approached by optimizing a subset of all inherent aspects (e.g. locations or number of drones vs. coverage, transmit power vs. interference, etc.) without taking into account other factors such as initial deployment and user clustering. In this paper, we target the problem of power minimization, interference mitigation, DSC localization, and user clustering jointly along with deci...