Energy Efficiency and Achievable Data Rate of Device-to-Device Communications in Cellular Networks

Device-to-Device (D2D) communications in cellular networks allow devices to communicate directly without going through the base station (BS). In this paper, we have established a D2D cooperative relaying scenario which is specified for LTE-Advanced and 5G systems networks. We analyze energy efficiency (EE) and achievable data rate (DR) for D2D communications underlaying cellular networks in three transmission modes, namely, cellular mode (CM), direct D2D mode (DM), and cooperative D2D mode (CoopD2D) where cellular user equipment (CUE) devices help each other to exchange information. We show that the location of CUEs, the distance between D2D users and the distance between D2D pairs and the base station are important factors for deciding which of the three modes should be used in order to achieve better EE and DR. We have also investigated the effects of choosing different numbers of relaying branches and relays in each branch on the performance of the network. This investigation leads to identifying optimal transmission schemes for maximizing EE and DR under varying environmental conditions.