  In this paper, energy-efficient transmission schemes achieving maximal
throughput over a finite time interval are studied in a problem setting
including energy harvests, data arrivals and channel variation. The goal is to
express the offline optimal policy in a way that facilitates a good online
solution. We express any throughput maximizing energy efficient offline
schedule (EE-TM-OFF) explicitly in terms of water levels. This allows per-slot
real-time evaluation of transmit power and rate decisions, using estimates of
the associated offline water levels. To compute the online power level, we
construct a stochastic dynamic program that incorporates the offline optimal
solution as a stochastic process. We introduce the "Immediate Fill" metric
which provides a lower bound on the efficiency of any online policy with
respect to the corresponding optimal offline solution. The online algorithms
obtained this way exhibit performance close to the offline optimal, not only in
the long run but also in short problem horizons, deeming them suitable for
practical implementations.
