  Battery-powered wireless IoT devices are now widely seen in many critical
applications. Given the limited battery capacity and inaccessibility to
external power recharge, optimizing energy efficiency (EE) plays a vital role
in prolonging the lifetime of these IoT devices. However, a sheer amount of
existing works only focus on the EE design at the infrastructure level such as
base stations (BSs) but with little attention to the EE design at the device
level. In this paper, we propose a novel idea that aims to shift energy
consumption to a grid-powered cognitive radio mesh network thus preserving
energy of battery-powered devices. Under this line of thinking, we cast the
design into a cross-layer optimization problem with an objective to maximize
devices' energy efficiency. To solve this problem, we propose a parametric
transformation technique to convert the original problem into a more tractable
one. A baseline scheme is used to demonstrate the advantage of our design. We
also carry out extensive simulations to exhibit the optimality of our proposed
algorithms and the network performance under various settings.
