Abstract
This paper investigates the optimal transmit beamforming design of simultaneous wireless information and power transfer (SWIPT) in the multiuser multiple-input-single-output (MISO) downlink with specific absorption rate (SAR) constraints. We consider the power splitting technique for SWIPT, where each receiver divides the received signal into two parts: one for information decoding and the other for energy harvesting with a practical non-linear rectification model. The problem of interest is to maximize as much as possible the received signal-to-interference-plus-noise ratio (SINR) and the energy harvested for all receivers, while satisfying the transmit power and the SAR constraints by optimizing the transmit beamforming at the transmitter and the power splitting ratios at different receivers. The optimal beamforming and power splitting solutions are obtained with the aid of semidefinite programming and bisection search. Low-complexity fixed beamforming and hybrid beamforming techniques are also studied. Furthermore, we study the effect of imperfect channel information and radiation matrices, and design robust beamforming to guarantee the worst-case performance. Simulation results demonstrate that our proposed algorithms can effectively deal with the radio exposure constraints and significantly outperform the conventional transmission scheme with power backoff.
Highlights
Compared to the traditional energy harvesting (EH) and green communication techniques, which collect energy from natural and man-made sources such as solar, wind or mechanical vibration, SWIPT can be fully controlled and optimized by harvesting energy from the radio-frequency (RF) signals
We focus on the PS approach and study the beamforming design in a multiuser MISO downlink channel, where the receivers are characterized by both communications
Two widely adopted regulations/measures on RF exposure are mainly considered i.e., the first one is the maximum permissible exposure (MPE) in [W/m2 ], which is defined as the highest level of electromagnetic radiation (EMR) to which a user may be exposed without incurring an established adverse health effect
Summary
IMULTANEOUS wireless information and power transfer (SWIPT) is a new technology where information and energy flows co-exist, co-engineered to simultaneously provide communication connectivity and energy sustainability [1], [2]. Two widely adopted regulations/measures on RF exposure are mainly considered i.e., the first one is the maximum permissible exposure (MPE) in [W/m2 ], which is defined as the highest level of electromagnetic radiation (EMR) to which a user may be exposed without incurring an established adverse health effect This is a important issue in the applications of wireless power transfer (WPT) and various relevant studies have been carried out concerning EMR. The integration of RF exposure constraints, and the SAR constraint, in the design of wireless communication systems is a timely research area with significant impact; few works in the literature take into account SAR regulations. In conventional single-antenna wireless communication systems, the SAR exposure limitation introduces an additional transmit power constraint, and can be .
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