Energy Efficiency and Spectral Efficiency Tradeoff for Asymmetric Two-Way AF Relaying With Statistical CSI

Both energy efficiency (EE) and spectral efficiency (SE) are two important design criteria that can hardly be achieved simultaneously. In this paper, we investigate the EE-SE tradeoff for a two-way relaying system with amplify-and-forward (AF) strategy. Applying a unified EE-SE tradeoff metric, a power-allocation problem is formulated as the joint EE and SE maximization problem with a tradeoff factor. In particular, only statistical channel-state information (CSI) is required, and the asymmetric traffic requirements are taken into consideration in our design. Through the exploitation of the theorem of nonlinear fractional programming, a unique closed-form optimum solution is obtained, and some useful insights are also achieved. It has been proved that the provided optimal solution is Pareto optimal for EE-SE optimization. Utilizing these results, one can flexibly make the tradeoff between EE and SE by simply setting the tradeoff factor. Simulation results highlight the effect of the proposed power-allocation scheme.