  We study the dynamic power splitting for simultaneous wireless information
and power transfer (SWIPT) in the ergodic fading channel. Considering the
nonlinearity of practical energy harvesting circuits, we adopt the realistic
nonlinear energy harvesting (EH) model rather than the idealistic linear EH
model. To characterize the optimal rate-energy (RE) tradeoff, we consider the
problem of maximizing the R-E region, which is nonconvex. We solve this
challenging problem for two different cases of the channel state information
(CSI): (i) when the CSI is known only at the receiver (the CSIR case) and (ii)
when the CSI is known at both the transmitter and the receiver (the CSI case).
For these two cases, we develop the corresponding optimal dynamic power
splitting schemes. To address the complexity issue, we also propose the
suboptimal schemes with low complexities. Comparing the proposed schemes to the
existing schemes, we provide various useful and interesting insights into the
dynamic power splitting for the nonlinear EH. Furthermore, we extend the
analysis to the scenarios of the partial CSI at the transmitter and the
harvested energy maximization. Numerical results demonstrate that the proposed
schemes significantly outperform the existing schemes and the proposed
suboptimal scheme works very close to the optimal scheme at a much lower
complexity.
