Device-to-device (D2D) communications underlayed to a cellular infrastructure has recently been proposed to increase spectrum and energy efficiency. Relay selection plays a vital role in cooperative networks. In D2D communication, if the chosen relay is not the best relay, then the whole communication will not be successful from source node to destination node. Also to choose the optimal relays, if more feedback and time delay exists between the source nodes and relay node then it leads to degradation of spectral efficiency. A survey on the relay selection techniques used with D2D communications and the challenges and design issues associated with the integration of D2D in 5G cellular network is presented.

Device-to-device (D2D) communications underlayed to a cellular infrastructure has recently been proposed to increase spectrum and energy efficiency. Relay selection plays a vital role in cooperative networks. In D2D communication, if the chosen relay is not the best relay, then the whole communicati...