Outage probability in an energy harvesting
(EH) block-fading communication system is studied in the
finite-horizon online setting. First, the offline version of
the problem is considered, and formulated as a mixed
integer linear program (MILP). Then, the infinite-horizon
online problem (IIL) is considered relaxing the battery
constraints. Solutions of these two problems provide lower
bounds on the finite-horizon online problem, for which we
provide a low-complexity heuristic scheme, called the fixed
threshold transmission (FTT) scheme. Numerical results
show that the FTT scheme achieves an outage performance
close to the MILP lower bound for a wide range of
operation regimes, and close to IIL when the EH rate is
low. It is also observed that the power allocated by the FTT
scheme resembles the optimal offline solution with high
probability, despite the lack of information about future
channel states and energy arrivals.