A Joint Relay Selection and Power Allocation Strategy for Multi-Hop D2D Communications

Device-to-device (D2D) communications has attracted the interest of researchers due to its potential for improving user experience and network stability. One of the key performance metrics in D2D communications is energy efficiency. To maximize the energy efficiency of proximity multi-hop D2D communications, this paper presents a joint relay selection and power allocation strategy based on the physical layer information and social network information. Specifically, we first calculate the transmission rate of each hop and derive an expression for end-to-end energy efficiency over a multi-hop link with the consideration of the interference from the cellular users. Then, we formulate a joint optimization problem to maximize the energy efficiency based on the social-aware characteristics of D2D communications. Despite the non-convexity of the formulated optimization problem, we present a low-complexity algorithm to find a sub-optimal solution. Numerical results show that the gap between the energy efficiency of the presented algorithm and that of the optimal strategy can be ignored. Besides, the substantial gain of the proposed algorithm has also been demonstrated.