Energy-Efficient Joint Power Allocation and Relay Selection in Bit Error Rate Constrained Two-Way Relay Network

Energy-Efficient Joint Power Allocation and Relay Selection in Bit Error Rate Constrained Two-Way Relay Network

Rashi Mehrotra (Department of Electrical Engineering, Indian Institute of Technology, Delhi, India) and Ranjan Bose (Department of Electrical Engineering and Bharti School of Telecommunication and Management, Indian Institute of Technology, Delhi, India)
DOI: 10.4018/IJITN.2015100101
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In this paper, the authors have proposed energy efficient power allocation and relay selection scheme in a two-way amplify-and-forward (AF) relay under bit error rate (BER) constrained network. They have derived an expression for the overall BER for Rayleigh fading channel. Based on minimum power consumption in the network, the authors have addressed the problem of power allocation by converting geometric programming to a convex optimization problem. A closed form solution of power allocation is found, which aims at minimizing total transmit power for the overall BER constrained network. The authors have evaluated minimum total transmit power for two-way AF relay network. Based on minimum total transmit power, a novel relay selection scheme has been proposed. Simulation results demonstrate that the proposed two-way power allocation and relay selection scheme can significantly minimize power consumption under BER constrained network as compared to the existing relay transmission. The proposed power allocation scheme gives 3 dBW gain than one-way relay transmission. The proposed relay selection method also outperforms the random relay selection by 24 dBW. The simulation results are corroborated with the analytical result
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1. Introduction

Energy efficiency (EE) has recently become a growing concern in both academia and industrial applications. Relaying is viewed as energy saving technique because it can reduce the transmit power by breaking one long range transmission into several short range transmission Han et al. (2011). Most relay systems are assumed to be operated in time division half-duplex (TDD) mode. For one-way relay, one source transmits data to one destination in two separate time slots with the help of relays. Such relaying protocol suffers performance loss in terms of spectral efficiency due to double time slots being used for transmission. To overcome the spectral efficiency loss, a two-way relaying protocol, an efficient bidirectional relaying scheme where two users exchange information via relay node(s) has been proposed. Very recently several researchers have focused on two-way relaying technique that has emerged as an effective approach to mitigate the spectral efficiency loss of conventional one-way relaying Rankov & Wittneben (2007).

Analyzing energy efficiency in two-way relaying has been recently a particular area of interest. In Sun & Yang (2012); (Sun & Yang, 2012) authors have compared EE of two-way relay with those of one way and direct transmission along with optimized relay position and transmit power at each node. Maximizing EE of orthogonal frequency division multiplexing signaling over a two-way amplify-and-forward (AF) relay network has been investigated in Sun et al. (2013). Energy efficient power allocation for two-way AF relay is considered in Li et al. (2011); Li et al. (2014); Sun et al. (2013) for certain data rate requirement. An optimal power allocation scheme for decode-and-forward (DF) two-way relay is proposed in Yu et al. (2013). In a two-way relay network, multiple relay cooperation improves spatial diversity and mitigate fading in wireless channels. Relay selection is considered a simple and effective approach to the cooperation. It reduces relay transmit power and synchronization overhead. Relay selection is considered a simple and effective approach to the cooperation. It reduces relay transmit power and synchronization overhead. Relay selection scheme with power allocation has been a significant area of interest Talwar et al. (2011); Do et al. (2013); Wang et al. (2013). Energy efficient transmission problem with relay selection criteria has gained a lot of importance recently in a two-way AF relay network Sun et al. (2012); Zhou et al. (2012); Huang et al. (2012); Jie et al. (2014). In Sun et al. (2012), a relay selection technique based on minimizing total transmit power constrained on signal-to-noise ratio (SNR) requirement on the two transceivers is considered. In Zhou et al. (2012), relay selection and power allocation were optimized for a two-way relay system that minimizes the total transmit power subject to the requirement of end-to-end rate. The authors in Huang et al. (2012) proposed a transmission scheme to minimize the energy consumed per bit transmitted for both one-way and two-way relay networks by joint relay selection and power allocation. In Jie et al. (2014), two-way outage constraints are considered to derive minimum transmit power in asymmetric traffic. To our knowledge there has been no work which has proposed relay selection and power allocation scheme under BER constrained network for energy efficient two-way AF relay.

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