  Powering cellular networks with renewable energy sources via energy
harvesting (EH) has recently been proposed as a promising solution for green
networking. However, with intermittent and random energy arrivals, it is
challenging to provide satisfactory quality of service (QoS) in EH networks. To
enjoy the greenness brought by EH while overcoming the instability of the
renewable energy sources, hybrid energy supply (HES) networks that are powered
by both EH and the electric grid have emerged as a new paradigm for green
communications. In this paper, we will propose new design methodologies for HES
green cellular networks with the help of Lyapunov optimization techniques. The
network service cost, which addresses both the grid energy consumption and
achievable QoS, is adopted as the performance metric, and it is optimized via
base station assignment and power control (BAPC). Our main contribution is a
low-complexity online algorithm to minimize the long-term average network
service cost, namely, the Lyapunov optimization-based BAPC (LBAPC) algorithm.
One main advantage of this algorithm is that the decisions depend only on the
instantaneous side information without requiring distribution information of
channels and EH processes. To determine the network operation, we only need to
solve a deterministic per-time slot problem, for which an efficient inner-outer
optimization algorithm is proposed. Moreover, the proposed algorithm is shown
to be asymptotically optimal via rigorous analysis. Finally, sample simulation
results are presented to verify the theoretical analysis as well as validate
the effectiveness of the proposed algorithm.
