Robust energy-efficient power allocation and relay selection for cooperative relay networks

One of the challenging issues in wireless relay networks is to choose the appropriate relays while keeping acceptable requirement of quality of service. In this paper, a joint optimal scheme of power allocation and relay selection is proposed for the decode-and-forward (DF) relay communication networks. The proposed scheme attempts to maximize the total energy-efficiency of the system. The cooperative relay and orthogonal frequency-division-multiple-access (OFDMA) technologies are introduced to improve the spectral efficiency. In order to reduce the effect caused by channel uncertainty, a robust power control approach based on worst case is applied. The formulated problem is a mixed-integer nonlinear problem, which is difficult to solve in the original form. Therefore, a novel relay selection scheme is formulated to transform it into a quasi-concave programming problem. The Dinkelbach method is used to solve the formulated optimization problem. Besides, a distributed iteration algorithm is developed to reduce the overhead of information exchange. Numerical results reveal the effectiveness of the proposed scheme and show better performance in aspect of outage reduction and energy efficiency improvement.