Relay selection and power allocation for energy-load efficient network-coded cooperative unicast D2D communications

The device-to-device (D2D) communication is one of the technologies proposed for the fifth generation (5G) of wireless networks, which enables the direct data transmission between the transmitter and the receiver without traversing the macrocell base station (MBS). Also, by evolving towards 5G, small cells are deployed to enhance the network's capacity, resulting in heterogeneous networks (HetNets). The dense deployment of small cell base stations (SBS) in the small geographical area makes them suitable relay candidates for cooperative communications. This paper aims to select a relay and transmit powers control to maximize energy efficiency and load balancing in random linear network coding (RLNC)-aided cooperative unicast D2D (RLNC D2D). The selected relay and allocated transmit powers, including the D2D transmitter and selected relay, should satisfy the conditions of the maximum transmit power and minimum spectral efficiency requirement. Jain’s fairness index is considered as the measure of load balancing. Then, the multi-objective problem is converted to the single-objective one to reduce the computational complexity. The results show that the proposed RLNC D2D improves the energy efficiency, spectral efficiency, load balancing, and outage probability compared to direct D2D communication.