Minimum transmit power under/considering relay selection for asymmetric two-way relaying networks

Two-way amplify-and-forward (AF) relaying networks have been widely studied because of their simplicity and high spectral efficiency characteristics. Power allocation (PA) and relay selection (RS) for two-way AF relaying systems are of particular interest. However, most of the previous studies only consider the PA and RS for these systems with symmetric traffic requirements. In this study, the authors´ focus on the minimum transmit power (MTP) under/considering RS for asymmetric two-way relaying networks. The authors´ derive the MTP required for two-way AF relaying transmission with asymmetric traffic requirements, and propose an optimal RS criterion based on the derived MTP. First, the outage probability (OP) of two-way relaying transmission based on statistical channel state information (CSI) is derived. Then, by converting a geometric programming to a convex optimisation problem, the closed-form solution of the PA aiming at minimising total transmit power under the OP constraints is obtained. Lastly, a distributed RS criterion based on MTP is proposed. In addition, the proposed RS scheme only needs local statistical CSI rather than instantaneous CSI, which makes it simple in implementation. Numerical results demonstrate that the proposed scheme can significantly decrease the power consumption under the predefined OP constraints.