Power Control for Achieving Energy-Efficient Multiuser Two-Way Balancing Relay Networks Keshav Singh ⋆ , Meng-Lin Ku † , and Jia-Chin Lin ‡ Department of Communication Engineering, National Central University, Taiwan, R.O.C. E-mail: keshav mp@yahoo.com ⋆ , mlku@ce.ncu.edu.tw † , jiachin@ce.ncu.edu.tw ‡ Abstract—Energy efficiency is a growing concern for the future wireless networks as energy consumption becomes a global environment problem. In this paper, an energy-efficient power control scheme is investigated for achieving the maximum energy efficiency in multiuser two-way balancing relay networks. We formulate the design problem as a ratio of the spectral efficiency over the entire energy consumption of the network under a total power constraint. An optimal power control scheme is proposed to iteratively improve the efficiency and finally reach the globally optimal solution. Compared with a heuristic scheme where the total available power is equally distributed among all nodes, the proposed scheme can dramatically improve not only the energy efficiency but also the spectral efficiency. I. I NTRODUCTION Relay networks have received a lot of interest to improve the network performance by expanding the coverage and increasing the capacity. The relay networks operated in a half- duplex mode suffer from a loss of spectral efficiency by a factor of 1/2. Unlike one-way relaying schemes, two-way relaying can help compensate the spectral efficiency loss by utilizing the radio resource in a more efficient manner. The energy consumption in wireless networks is swiftly increasing with the rapid growth of wireless applications [1],[2]. Thus, the design of energy-efficient relay networks becomes an challenging issue toward green communications [3],[4]. In addition to energy saving, energy-efficient communications can provide the benefit of reducing interference to other users as well as lessening the environmental impact. The power consumption of wireless networks can be clas- sified into two folds: dynamic and static. In general, the circuit power is static and independent of channel conditions, while the transmit power level is adapted to the instantaneous channel conditions. In this paper, we investigate a power control problem for multiuser two-way relay networks and intend to maximize the energy efficiency by considering both the static and dynamic power consumption. Recently, the energy efficiency has become a paramount factor for designing multiuser two-way relay networks. More- over, the available spectrum resource needs to be efficiently utilized for achieving an acceptable data rate. Consequently, there is a performance trade-off between the spectral effi- ciency and the energy efficiency. Energy-efficient wireless networks have addressed in several works [5]–[12]. In [5], interference management and resource allocation were inves- tigated in designing an energy-efficient access network, while a network architecture in terms of antenna placement and macro-cell/micro-cell selection was optimized for minimizing the energy consumption [6]. The authors in [7] proposed opportunistic schemes to decide which subset of the relay nodes cooperates together in order to minimize the energy consumption. It was claimed in [10] that two-way relaying is not always energy-efficient when taking the self-interference and the receiver processing energy consumption into account. However, most of the previous works on energy efficiency were merely considered in single-user scenarios and focused on minimizing the energy consumption in the network. The optimal power control for maximizing the energy efficiency of multiuser two-way relay interference networks has not been addressed prior to our work. In contrast to the aforementioned works, we emphasis on power control schemes for multiuser two-way relay networks in order to improve energy efficiency under a total power constraint, while balancing the rates of the forward and backward links. The multiuser two-way relay network consists of N source-destination pairs and one relay node, each of which is equipped with a single antenna. The relay helps both the source and destination nodes in forwarding the signals to their corresponding pair nodes through an amplify-and- forward (AF) strategy [13]. The bits-per-Joule-per-Hertz is adopted as the performance metric for the network energy efficiency. With the considered design problem, an energy- efficient power control algorithm is proposed to iteratively enhance the energy efficiency and finally attain the globally optimal solution. The remainder of this paper is organized as follows. The system model and problem formulation are introduced in Sec- tion II. The optimal power control for achieving the maximum energy efficiency is designed in Section III. Numerical results are presented in Section IV. Finally, conclusions are drawn in Section V.        Fig. 1. A multiuser two-way relay network. 2014 IEEE International Conference on Acoustic, Speech and Signal Processing (ICASSP) 978-1-4799-2893-4/14/$31.00 ©2014 IEEE 2749