Online Power and Time Allocation in MIMO Uplink Transmissions Powered by RF Wireless Energy Transfer

Wireless energy transfer (WET) has been a promising technology to tackle the lifetime bottlenecks of energy-limited wireless devices in recent years. In this paper, we study a WET-enabled multiple-input multiple-output system including a base station (BS) and a user equipment (UE), which has a finite battery capacity. We consider slotted transmissions, where each slot includes two phases, namely, a downlink (DL) WET phase and an uplink (UL) wireless information transmission (WIT) phase. In the WET phase (a fraction <inline-formula><tex-math notation="LaTeX">$\tau$ </tex-math></inline-formula> of a slot), the BS transfers energy and the UE stores the received energy in the battery. In the WIT phase (a fraction <inline-formula><tex-math notation="LaTeX">$1-\tau$</tex-math></inline-formula> of a slot), the UE transmits information to the BS by using the energy in the battery. Considering the power sensitivity <inline-formula><tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula> of the radio frequency to DC conversion circuits, the BS transfers energy only if the UE received power is larger than <inline-formula> <tex-math notation="LaTeX">$\alpha$</tex-math></inline-formula>, and the DL WET is formulated as a Bernoulli process. Based on the formulation, we propose an online power and time allocation algorithm to maximize the average data rate of UL WIT. We also extend the proposed algorithm to multiple user systems. The numerical results show that the proposed algorithm outperforms the existing schemes in terms of average data rate, energy efficiency, and outage probability.