  In recent years, wireless communication systems are expected to achieve more
cost-efficient and sustainable operations by replacing conventional fixed power
supplies such as batteries with energy harvesting (EH) devices, which could
provide electric energy from renewable energy sources (e.g., solar and wind).
Such EH power supplies, however, are random and instable in nature, and as a
result impose new challenges on reliable communication design and have
triggered substantial research interests in EH based wireless communications.
Building upon existing works, in this article, we develop a general
optimization framework to maximize the utility of EH wireless communication
systems. Our framework encapsulates a variety of design problems, such as
throughput maximization and outage probability minimization in single-user and
multiuser setups, and provides useful guidelines to the practical design of
general EH based communication systems with different assumptions over the
knowledge of time-varying wireless channels and EH rates at the transmitters.
