Information-Energy Region for SWIPT Networks in Mobility Scenarios

This paper studies the information-energy (<inline-formula><tex-math notation="LaTeX">$\mathrm{I}$</tex-math></inline-formula>-<inline-formula><tex-math notation="LaTeX">$\mathrm{E}$</tex-math></inline-formula>) region for simultaneous wireless information and power transfer (SWIPT) networks in mobility scenarios, where a moving transmitter simultaneously transmits information and power to a fixed receiver, and the receiver adopts power splitting (PS) receiving architecture. In order to characterize the tradeoff between the received information and harvested energy, the <inline-formula><tex-math notation="LaTeX">$\mathrm{I}$</tex-math></inline-formula>-<inline-formula><tex-math notation="LaTeX">$\mathrm{E}$</tex-math></inline-formula> region is defined, and corresponding optimization problems are formulated to explore the system <inline-formula><tex-math notation="LaTeX">$\mathrm{I}$</tex-math></inline-formula>-<inline-formula><tex-math notation="LaTeX">$\mathrm{E}$</tex-math></inline-formula> regions by jointly optimizing the transmit power at the transmitter and the PS ratio at the receiver with three popular energy harvesting (EH) models, i.e., traditional linear EH model, the logistic nonlinear EH model and the piecewise nonlinear EH model. Particularly, to efficiently solve the nonconvex optimization problem with the logistic nonlinear EH model, a successive convex approximate (SCA)-based algorithm is proposed, which is able to characterize the lower bound of the <inline-formula><tex-math notation="LaTeX">$\mathrm{I}$</tex-math></inline-formula>-<inline-formula><tex-math notation="LaTeX">$\mathrm{E}$</tex-math></inline-formula> with low complexity. To solve the optimization problems with the linear and piecewise EH models, as they are convex, some closed and semi-closed solutions are derived by using Lagrange dual method and KKT conditions. Numerical results show that compared with the <inline-formula><tex-math notation="LaTeX">$\mathrm{I}$</tex-math></inline-formula>-<inline-formula><tex-math notation="LaTeX">$\mathrm{E}$</tex-math></inline-formula> regions under the linear and piecewise EH models, that under the logistic nonlinear EH model is smaller due to the limitations of practical EH circuit features. Moreover, with a fixed moving speed, when the transmit power is relatively large, the logistic nonlinear EH model can be replaced with the piecewise one due to the relatively small gap between their achieved <inline-formula><tex-math notation="LaTeX">$\mathrm{I}$</tex-math></inline-formula>-<inline-formula><tex-math notation="LaTeX">$\mathrm{E}$</tex-math></inline-formula> regions. Additionally, for a fixed moving track length, the higher moving speed yields the smaller <inline-formula><tex-math notation="LaTeX">$\mathrm{I}$</tex-math></inline-formula>-<inline-formula><tex-math notation="LaTeX">$\mathrm{E}$</tex-math></inline-formula> region with all three EH models.