Rate-Energy Tradeoffs of Wireless Powered Backscatter Communication With Power Splitting and Time Switching

We consider a monostatic wireless powered backscatter communication (WPBC) system, where a device performs backscatter modulation and energy harvesting (EH) using the received signal from a multi-antenna hybrid access point. The rate-energy regions of the WPBC are studied for power splitting (PS) and time switching (TS) receivers in a comprehensive way by using the rate and EH functions reflecting the effects of practical systems. For both linear and nonlinear EH models, we analyze the rate-energy regions of the static PS and TS strategies and optimize the dynamic strategies exploiting the channel state information (CSI) to extend the regions. The regions with the static strategies are obtained in closed-form expressions and the dynamic strategies are obtained in explicit forms as a function of a dual variable, by approximating the nonlinear EH model to a piecewise linear EH (PLEH) model. The results show that the dynamic PS and TS strategies outperform their static counterparts and their gains are more prominent in the sensitivity region of a nonlinear EH circuit and with a smaller number of antennas. It is also observed that the dynamic PS strategy provides the best performance but can be replaced by the static one for a large number of antennas to avoid the CSI. The strategies obtained explicitly by using the PLEH model are also shown to work well with a practical EH model without a noticeable loss in the performance.