20 research outputs found
Signal and System Design for Wireless Power Transfer : Prototype, Experiment and Validation
A new line of research on communications and signals design for Wireless
Power Transfer (WPT) has recently emerged in the communication literature.
Promising signal strategies to maximize the power transfer efficiency of WPT
rely on (energy) beamforming, waveform, modulation and transmit diversity, and
a combination thereof. To a great extent, the study of those strategies has so
far been limited to theoretical performance analysis. In this paper, we study
the real over-the-air performance of all the aforementioned signal strategies
for WPT. To that end, we have designed, prototyped and experimented an
innovative radiative WPT architecture based on Software-Defined Radio (SDR)
that can operate in open-loop and closed-loop (with channel acquisition at the
transmitter) modes. The prototype consists of three important blocks, namely
the channel estimator, the signal generator, and the energy harvester. The
experiments have been conducted in a variety of deployments, including
frequency flat and frequency selective channels, under static and mobility
conditions. Experiments highlight that a channeladaptive WPT architecture based
on joint beamforming and waveform design offers significant performance
improvements in harvested DC power over conventional
single-antenna/multiantenna continuous wave systems. The experimental results
fully validate the observations predicted from the theoretical signal designs
and confirm the crucial and beneficial role played by the energy harvester
nonlinearity.Comment: Accepted to IEEE Transactions on Wireless Communication
Waveform design for Wireless Power Transfer
Far-field Wireless Power Transfer (WPT) has attracted significant attention in recent years. Despite the rapid progress, the emphasis of the research community in the last decade has remained largely concentrated on improving the design of energy harvester (so-called rectenna) and has left aside the effect of transmitter design. In this paper, we study the design of transmit waveform so as to enhance the dc power at the output of the rectenna. We derive a tractable model of the nonlinearity of the rectenna and compare with a linear model conventionally used in the literature. We then use those models to design novel multisine waveforms that are adaptive to the channel state information (CSI). Interestingly, while the linear model favours narrowband transmission with all the power allocated to a single frequency, the nonlinear model favours a power allocation over multiple frequencies. Through realistic simulations, waveforms designed based on the nonlinear model are shown to provide significant gains (in terms of harvested dc power) over those designed based on the linear model and over nonadaptive waveforms. We also compute analytically the theoretical scaling laws of the harvested energy for various waveforms as a function of the number of sinewaves and transmit antennas. Those scaling laws highlight the benefits of CSI knowledge at the transmitter in WPT and of a WPT design based on a nonlinear rectenna model over a linear model. Results also motivate the study of a promising architecture relying on large-scale multisine multiantenna waveforms for WPT. As a final note, results stress the importance of modeling and accounting for the nonlinearity of the rectenna in any system design involving wireless power
IRS-Aided SWIPT: Joint Waveform, Active and Passive Beamforming Design Under Nonlinear Harvester Model
The performance of Simultaneous Wireless Information and Power Transfer
(SWIPT) is mainly constrained by the received Radio-Frequency (RF) signal
strength. To tackle this problem, we introduce an Intelligent Reflecting
Surface (IRS) to compensate the propagation loss and boost the transmission
efficiency. This paper proposes a novel IRS-aided SWIPT system where a
multi-carrier multi-antenna Access Point (AP) transmits information and power
simultaneously, with the assist of an IRS, to a single-antenna User Equipment
(UE) employing practical receiving schemes. Considering harvester nonlinearity,
we characterize the achievable Rate-Energy (R-E) region through a joint
optimization of waveform, active and passive beamforming based on the Channel
State Information at the Transmitter (CSIT). This problem is solved by the
Block Coordinate Descent (BCD) method, where we obtain the active precoder in
closed form, the passive beamforming by the Successive Convex Approximation
(SCA) approach, and the waveform amplitude by the Geometric Programming (GP)
technique. To facilitate practical implementation, we also propose a
low-complexity design based on closed-form adaptive waveform schemes.
Simulation results demonstrate the proposed algorithms bring considerable R-E
gains with robustness to CSIT inaccuracy and finite IRS states, and emphasize
the importance of modeling harvester nonlinearity in the IRS-aided SWIPT
design.Comment: Source code available at
https://github.com/SnowzTail/irs-aided-swipt-joint-waveform-active-and-passive-beamforming-design-under-nonlinear-harvester-mode
Waveform and Beamforming Design for Intelligent Reflecting Surface Aided Wireless Power Transfer: Single-User and Multi-User Solutions
In this paper, we study the waveform and passive beamforming design for
intelligent reflecting surface (IRS)-aided wireless power transfer (WPT).
Generalized multi-user and low complexity single-user algorithms are derived
based on alternating optimization (AO) framework to maximize the weighted sum
output DC current, subject to transmit power constraints and passive
beamforming phases unit modulus constraints. The input signal waveform and IRS
passive beamforming phase shifts are jointly designed as a function of users'
individual frequency-selective channel state information (CSI). The energy
harvester nonlinearity is explored and two IRS deployment schemes, namely
frequency selective IRS (FS-IRS) and frequency flat IRS (FF-IRS), are modeled
and analyzed. This paper highlights the fact that IRS can provide an extra
passive beamforming gain on output DC power over conventional WPT designs and
significantly influence the waveform design by leveraging the benefit of
passive beamforming, frequency diversity and energy harvester nonlinearity.
Even though FF-IRS exhibits lower output DC current than FS-IRS, it still
achieves substantially increased DC power over conventional WPT designs.
Performance evaluations confirm the significant benefits of a joint waveform
and passive beamforming design accounting for the energy harvester nonlinearity
to boost the performance of single-user and multi-user WPT system.Comment: 32 pages, 19 figures, submitted for publicatio