Energy-efficient resource allocation for amplify-and-forward relaying in OFDM systems

In this paper, we study end-to-end energy efficiency of an orthogonal frequency-division multiplexing relay-based system under power constraints for the base station and relay node with system circuit power considerations. Using a two-phase amplify-and-forward relaying protocol, we assume that relay has a fixed power constraint and the source power can vary in transmission power interval where the source employs a selective relaying mechanism for each individual subcarrier. Therefore, in our model, the source is able to adaptively select some subcarriers to be relayed. The radio resource allocation is then formulated as an energy-efficient mixed binary integer programming, and then we propose a heuristic algorithm to find the suboptimal solution. The solution consists of the suboptimal transmit power of the source, the suboptimal set of subcarriers for relaying and the optimal transmit power of each subcarrier at the source and relay in the first and second time slots. The algorithm obtains energy-efficient transmission power for a given relay transmission power based on a gradient descent method. Then a two-step iterative scheme is proposed to obtain the subcarriers to be relayed as well as the optimal power allocation at the source and relay in the first and second time slots. To evaluate the efficiency of the proposed method, we compare its efficiency through simulations with the cases without using selective subcarrier relaying and without circuit power consideration in low and high relay transmit power regimes. The simulation results indicate that using our proposed method results in a significant improvement in the energy efficiency. Copyright © 2014 John Wiley & Sons, Ltd. *Correspondence Jafar Kazemi, Electrical and Computer Engineering Department, Isfahan University of Technology, Isfahan, Iran. E-mail: [email protected]. Received 11 April 2014; Revised 18 June 2014; Accepted 13 July 2014