Joint energy-aware and buffer-assisted relay selection method for relay-aided D2D communications

Device-device (D2D) communications is an effective technique to improve performance on overall throughput and energy efficiency in cellular network. However, owing to the long separation distance or poor link quality between the source and destination user device (UD), the advantages of D2D communications are limited by only using direct D2D communications. For improving the system performance of cellular network, relay-aided D2D communications was put forward as a complement for direct D2D communications. The purpose of this article is to devise a relay selection method that improves the D2D communications performance. In this paper, we propose an Energy-Aware and Buffer-Assisted (EABA) relay selection method that take account of several conditions jointly, including transmission rate, relay-available UD (RUD) residual energy, and RUD buffer state. At each time slot, according to the channel state, energy, and buffer size, a scheduling rule is calculated dynamically by the EABA relay selection method. And then, which of the links activated to transmit packet is specified by the scheduling rule. Numerical examples are presented to show the performance of the EABA method.