  Energy Harvesting (EH) has emerged as a promising technique for Green
Communications and it is a novel technique to prolong the lifetime of the
wireless networks with replenishable nodes. In this paper, we consider the
energy shortage analysis of fixed rate transmission in communication systems
with energy harvesting nodes. First, we study the finite-horizon transmission
and provide the general formula for the energy shortage probability. We also
give some examples as benchmarks. Then, we continue to derive a closed-form
expression for infinite-horizon transmission, which is a lower bound for the
energy shortage probability of any finite-horizon transmission. These results
are proposed for both Additive White Gaussian Noise (AWGN) and fading channels.
Moreover, we show that even under \emph{random energy arrival}, one can
transmit at a fixed rate equal to capacity in the AWGN channels with negligible
aggregate shortage time. We achieve this result using our practical
transmission schemes, proposed for finite-horizon. Also, comprehensive
numerical simulations are performed in AWGN and fading channels with no Channel
State Information (CSI) available at the transmitter, which corroborate our
theoretical findings. Furthermore, we improve the performance of our
transmission schemes in the fading channel with no CSI at the transmitter by
optimizing the transmission initiation threshold.
