Fair and Energy-efficient Cooperative Relaying with Selfish Nodes Jun Fan † , Zhengguo Sheng ‡ , Chi Harold Liu † , Athanasios V. Vasilakos ♮ , and Xiumei Fan † † Beijing Institute of Technology, China, ‡ France Telecom Orange Labs, Beijing, China, ♮ Kuwait University, Kuwait E-mail: † {jfan,xmfan}@bit.edu.cn , ‡ zhengguo.sheng@orange.com, † chiliu@ieee.org, ♮ th.vasilakos@gmail.com Abstract—Cooperative communication has been proven effec- tive in enhancing the performance of wireless networks. In this paper, we propose an adaptive multi-relay selection with power allocation mechanism to offer energy fairness at each node for a cooperative network. Unlike traditional approaches where all nodes are considered to transmit in a collaborative manner, we explicitly consider the situation where each node exhibits some degree of selfishness behavior. By introducing novel concepts of the selfishness index and utility function which denote node’s benefit from cooperation, we show that the proposed cooperation scheme can well balance the energy consumption among nodes as well as maximize the network lifetime. Theoretical analysis and extensive simulation results are supplemented to show advantages of the proposed approach in power saving and power allocation fairness. I. I NTRODUCTION In wireless communication, signal fading caused by multi- path propagation is a particularly serious channel detriment. In order to address this issue, cooperative communication mechanisms [1], [2] have been proposed as an effective way of exploiting spatial diversity to improve the quality of wireless links. By encouraging single-antenna devices to share their antennas cooperatively, a number of potential benefits can be achieved, including the improved reception reliability, reduced power consumption and increased spectrum efficiency [3], [4]. Although the idea of cooperative communication has been proposed for almost a decade, there are still fundamental issues to be considered from theoretical analysis perspectives; and in particular, we focus on the fundamental issue of relay selection in this paper. In existing literatures, a number of schemes have been proposed, ranging from single relay selection [5], [6] to multi-relay selection [7]–[9]. However, none of these work considers the fair usage of energy consumption, especially for relay nodes. Motivated by the recent research on the study of the inherent loss of efficiency caused to a system by the participant’s selfishness [10], we explicitly consider the impact of selfish behavior on relay selection and uniquely propose an effective mechanism to achieve the energy fairness. More specifically, in this paper, we propose a cooperation scheme to jointly consider relay selection and power allocation by incorporating fairness and selfish natures of wireless nodes. We capture the selfish behavior in wireless networks by introducing a selfishness index which represents the time- varying selfish level of each node, and incorporate this index into a novel utility function which denotes the net payoff of a node from cooperative transmission. Higher utility values denote more responsibility in the cooperative transmission; This work was supported by Natural Science Foundation of China (No. 61272509), the Projects of Major International (Regional) Joint Research Program NSFC (No. 61120106010), and Beijing Natural Science Foundation (No. 4132049). Source Destination Active relay set nodes in total Transmission in the first slot Transmission in the second slot N Fig. 1. Cooperative transmission model with multiple relays. while for the purpose of decreasing power consumption, a node with lower utility can show some degree of selfishness to reserve energy. The contribution of the paper is three-fold: • We explicitly derive a closed-form solution for the outage probability of a multi-relay cooperation scheme employ- ing repetition-coded Decode-and-Forward (DF) strategy. • We incorporate a novel concept of selfishness index into a utility function to uniquely capture and regulate the selfish behavior of a node in the proposed relay selection strategy. • We propose a two-step relay selection mechanism cover- ing all aspects of power efficiency, energy consumption fairness and network lifetime. The remainder of this paper is organized as follows. In Section II, we present the system model, derive the closed- form expression of outage probability, and define the utility parameter with selfishness index. The proposed approach of relay selection and power allocation is introduced in Section III and IV. Simulation results are shown in Section V, followed by concluding remarks in Section VI. II. SYSTEM MODEL We consider a wireless cooperative, relay network N con- sisting of N nodes, where N  {i =1, 2,...,N }. All nodes possess the same initial energy reserve, denoted as E i , and the residual energy at time t is denoted as ¯ E i (t), ∀i ∈N . We assume a discrete system operation where time is divided into discrete time slots, and TDMA is used to provide collision- free transmissions from the source and relays [1]. As in [8], we assume full channel state information is available at source, where centralized relay selection and power allocation is performed. We assume that relay transmissions are half- duplex such that they cannot send and receive packets at the same time. All channels exhibit Additive White Gaussian Noise (AWGN). Finally, the fading is assumed to be stationary, with frequency non-selective Rayleigh block fading. 978-1-4673-3122-7/13/$31.00 ©2013 IEEE IEEE ICC 2013 - Selected Areas in Communications Symposium 2795