  In this work, communication over a time-correlated point-to-point wireless
channel is studied for an energy harvesting (EH) transmitter. In this model, we
take into account the time and energy cost of acquiring channel state
information. At the beginning of the time slot, the EH transmitter, has to
choose among three possible actions: i) deferring the transmission to save its
energy for future use, ii) transmitting without sensing, and iii) sensing the
channel before transmission. At each time slot, the transmitter chooses one of
the three possible actions to maximize the total expected discounted number of
bits transmitted over an infinite time horizon. This problem can be formulated
as a partially observable Markov decision process (POMDP) which is then
converted to an ordinary MDP by introducing a belief on the channel state, and
the optimal policy is shown to exhibit a threshold behavior on the belief
state, with battery-dependent threshold values. Optimal threshold values and
corresponding optimal performance are characterized through numerical
simulations, and it is shown that having the sensing action and intelligently
using it to track the channel state improves the achievable long-term
throughput significantly.
