  The transmission scheduling is a critical problem in radio frequency (RF)
energy harvesting communications. Existing transmission strategies in an
RF-based energy harvesting system is mainly based on a classic model, in which
the data transmission is scheduled in a fixed feasible energy tunnel. In this
paper, we re-examine the classic energy harvesting model and show through the
theoretical analysis and experimental results that the bounds of feasible
energy tunnel are dynamic, which can be affected by the transmission scheduling
due to the impact of residual energy on the harvested one. To describe a
practical energy harvesting process more accurately, a new model is proposed by
adding a feedback loop that reflects the interplay between the energy harvest
and the data transmission. Furthermore, to improve network performance, we
revisit the design of an optimal transmission scheduling strategy based on the
new model. To handle the challenge of the endless feedback loop in the new
model, a recursive algorithm is developed. The simulation results reveal that
the new transmission scheduling strategy can balance the efficiency of energy
reception and energy utilization regardless of the length of energy packets,
achieving improved throughput performance for wireless communications.
