  The difficulty of modeling energy consumption in communication systems leads
to challenges in energy harvesting (EH) systems, in which nodes scavenge energy
from their environment. An EH receiver must harvest enough energy for
demodulating and decoding. The energy required depends upon factors, like code
rate and signal-to-noise ratio, which can be adjusted dynamically. We consider
a receiver which harvests energy from ambient sources and the transmitter,
meaning the received signal is used for both EH and information decoding.
Assuming a generalized function for energy consumption, we maximize the total
number of information bits decoded, under both average and peak power
constraints at the transmitter, by carefully optimizing the power used for EH,
power used for information transmission, fraction of time for EH, and code
rate. For transmission over a single block, we find there exist problem
parameters for which either maximizing power for information transmission or
maximizing power for EH is optimal. In the general case, the optimal solution
is a tradeoff of the two. For transmission over multiple blocks, we give an
upper bound on performance and give sufficient and necessary conditions to
achieve this bound. Finally, we give some numerical results to illustrate our
results and analysis.
