  Mitigating climate change and its impacts is one of the sustainable
development goals (SDGs) required by United Nations for an urgent action.
Increasing carbon emissions due to human activities is the root cause to
climate change. Telecommunication networks that provide service connectivity to
mobile users contribute great amount of carbon emissions by consuming lots of
non-renewable energy sources. Beyond the improvement on energy efficiency, to
reduce the carbon footprint, telecom operators are increasing their adoption of
renewable energy (e.g., wind power). The high variability of renewable energy
in time and location; however, creates difficulties for operators when
utilizing renewables for the reduction of carbon emissions. In this paper, we
consider a heterogeneous network consisted of one macro base station (MBS) and
multiple small base stations (SBSs) where each base station (BS) is powered by
both of renewable and non-renewable energy. Different from the prior works that
target on the total power consumption, we propose a novel scheme to minimize
the carbon footprint of networks by dynamically switching the ON/OFF modes of
SBSs and adjusting the association between users and BSs to access renewables
as much as possible. Our numerical analysis shows that the proposed scheme
significantly reduces up to 86% of the nonrenewable energy consumption compared
to two representative baselines.

Distributed, Parallel, and Cluster Computing