  Energy harvesting in cellular networks is an emerging technique to enhance
the sustainability of power-constrained wireless devices. This paper considers
the co-channel deployment of a macrocell overlaid with small cells. The small
cell base stations (SBSs) harvest energy from environmental sources whereas the
macrocell base station (MBS) uses conventional power supply. Given a stochastic
energy arrival process for the SBSs, we derive a power control policy for the
downlink transmission of both MBS and SBSs such that they can achieve their
objectives (e.g., maintain the signal-to-interference-plus-noise ratio (SINR)
at an acceptable level) on a given transmission channel. We consider a
centralized energy harvesting mechanism for SBSs, i.e., there is a central
energy storage (CES) where energy is harvested and then distributed to the
SBSs. When the number of SBSs is small, the game between the CES and the MBS is
modeled as a single-controller stochastic game and the equilibrium policies are
obtained as a solution of a quadratic programming problem. However, when the
number of SBSs tends to infinity (i.e., a highly dense network), the
centralized scheme becomes infeasible, and therefore, we use a mean field
stochastic game to obtain a distributed power control policy for each SBS. By
solving a system of partial differential equations, we derive the power control
policy of SBSs given the knowledge of mean field distribution and the available
harvested energy levels in the batteries of the SBSs.
