A Virtual MIMO Communication for a UAV-Enabled Cognitive Relay Network

In this article, a disaster response network (DRN) aided by an unmanned aerial vehicle (UAV) is studied. We consider a number of uplink cellular users as primary users (PUs), active device-to-device (D2D) users as secondary users (SUs), and idle D2D users which act as a virtual multiple-input multiple-output (MIMO) node. All the nodes have been equipped with a single antenna. The virtual MIMO node receives the signals from the cellular users and forwards them toward the UAV using a beamforming (BF) method to maximize the received signal-to-interference plus noise ratio (SINR) at the UAV while satisfying the quality of service (QoS) of the D2D receivers. The corresponding optimization problem is convex and the Lagrange function is defined to satisfy Karush–Kuhn–Tucker (KKT) conditions to calculate the BF vector. The probabilities of successful (POS) D2D and uplink transmissions are also introduced to define the system rate. In addition, the optimal value of the height of UAV is calculated using the simulation results. The numerical results show the effectiveness of the proposed strategy.