I. Introduction
In D2D communications, two user equipments (UEs) directly communicate with each other without having the payload traversed through the backhaul network. Due to its local communications nature, D2D communication can be provided with a lower cost than cellular communications. Furthermore, D2D communications provides many benefits unavailable to uncoordinated communications [2]–[4]. There are many current and prospective applications for D2D communications. For example, D2D has been proposed for use in LTE-based public safety networks for its security and reliability [5]. Additionally, D2D communications is necessary for the scenarios where cellular transmission is not accessible [4].