Radio waves carry both energy and information simultaneously. Nevertheless, radio-frequency (RF) transmissions of these quantities have traditionally been treated separately. Currently, the community is experiencing a paradigm shift in wireless network design, namely, unifying wireless transmission of information and power so as to make the best use of the RF spectrum and radiation as well as the network infrastructure for the dual purpose of communicating and energizing. In this paper, we review and discuss recent progress in laying the foundations of the envisioned dual purpose networks by establishing a signal theory and design for wireless information and power transmission (WIPT) and identifying the fundamental tradeoff between conveying information and power wirelessly. We start with an overview of WIPT challenges and technologies, namely, simultaneous WIPT (SWIPT), wirelessly powered communication networks (WPCNs), and wirelessly powered backscatter communication (WPBC). We then characterize energy harvesters and show how WIPT signal and system designs crucially revolve around the underlying energy harvester model. To that end, we highlight three different energy harvester models, namely, one linear model and two nonlinear models, and show how WIPT designs differ for each of them in single-user and multi-user deployments. Topics discussed include rate-energy region characterization, transmitter and receiver architectures, waveform design, modulation, beamforming and input distribution optimizations, resource allocation, and RF spectrum use. We discuss and check the validity of the different energy harvester models and the resulting signal theory and design based on circuit simulations, prototyping, and experimentation. We also point out numerous directions that are promising for future research.

Fundamentals of Wireless Information and Power Transfer: From RF Energy Harvester Models to Signal and System Designs

With a consumer and / or energy storage device, from the or the mobile moving body 3 moving on or roadway or rail is stopped, apparatus for inducing transmitting electrical energy, the roadway 1 comprising a floor derivative 5 which is attached, this floor derivative with a number of first induction coil 4 connected to the arranged and power along the roadway 1 or rail, the first induction coil towards the mobile 3 It has a magnetic conductive iron core 6 to generate a magnetic field oriented in. Inductive wheel 8 attached to the movable body 3 is magnetically conductive core 10 and the second induction coil 9 fixed with a magnetically conductive wheel disc 11 facing towards the linked roadway 1 or rails on both sides of the core , and a 12. To ensure low reluctance loss between and induction coil 4, 9 for contacting the road 1, the magnetic conductivity of the tire 13 is attached to the wheel disc by an elastic which is rotated by the movement of the object 3, the tire flat in the pressed state, to reliably bridge the gap remaining between the roadway and wheel disc. This device is advantageously used in conjunction with an electric vehicle in order to comfortably and quickly recharge the battery during or in parked cars.

Apparatus for transmitting electrical energy

The future Internet-of-Things network is expected to connect billions of sensors, which incurs high latency for data aggregation. To overcome this challenge, a new technique called over-the-air function computation was recently developed to enable fusion center to receive a desired function directly. It utilizes the superposition property of wireless channel to realize the uniform summation of the desired function. In order to compensate the non-uniform fading of different sensors, we propose a novel uniform-forcing transceiver design for over-the-air function computation. A corresponding min-max optimization problem is formulated to minimize the distortion of the computation which is measured by mean squared error. Due to the non-convexity of the problem, it is relaxed to semidefinite programming first. Then, the performance of the initial solution is improved through successive convex approximation. Simulation results show that the proposed design is able to achieve significant performance gain with low complexity.

A Uniform-Forcing Transceiver Design for Over-the-Air Function Computation

The evolution of the Internet of Things (IoT) over the past 20 years

Ambient backscatter (AB), making use of both energy harvesting and backscattering, has recently become a promising solution to communications among low-power devices and demonstrates its potential application in the Internet of Things. Existing AB systems adopt two-state amplitude shift keying or phase shift keying (PSK), where data are transmitted at the rate of one bit per symbol period. To increase the data rate, we investigate the high-order modulation where ${M}$ -PSK is employed for backscattering. We derive the optimal multilevel energy detector and compute the closed-form symbol error rate. To show the realizability of the proposed design, we build a 4PSK-AB hardware prototype, in which the selection of load impedance is discussed with the aid of phasor diagram illustration. The hardware prototype can achieve the date rate of 20 kb/s. Besides, higher date rate is achievable for 98.7% of the time compared with binary AB communications, and the mean number of distinguishable symbols is 3.66.

IoT Communications With $M$ -PSK Modulated Ambient Backscatter: Algorithm, Analysis, and Implementation

The wireless power transfer via an electro-magnetic (EM) wave enables far-field power transfer for supplying power to Internet of Things (IoT) devices. However, the power attenuation of the EM wave leads to low end-to-end power transfer efficiency. In this paper, we provide an analytic and experimental study on the distributed wireless power transfer system as a means to overcome the low power transfer efficiency. In the distributed wireless power transfer system, a number of multiantenna power beacons, which are distributed over space, send out wireless power to charge IoT devices. Since each power beacon has a separate local oscillator and controller, it is very challenging to achieve frequency and phase synchronization among power beacons, which is the prerequisite for optimal distributed beamforming. In this paper, we study the performance of the distributed wireless power transfer system with or without the frequency and phase synchronization. Based on the experiment and simulation results, we show that the distributed wireless charging is advantageous in terms of the coverage probability as long as the optimal distributed beamforming is available in the distributed wireless power transfer system.

Distributed Wireless Power Transfer System for Internet of Things Devices

We propose and implement a novel 1-bit coding metasurface that is capable of focusing and steering beam for enhancing power transfer efficiency of the electromagnetic (EM) wave-based wireless power transfer systems. The proposed metasurface comprises 16 × 16 unit cells which are designed with a fractal structure and the operating frequency of 5.8 GHz. One PIN diode is incorporated within each unit cell and enables two states with 180 ° phase change of the reflected signal at the unit cell. The two states of the unit cell correspond to the ON and OFF states of the PIN diode or “0” and “1” coding in the metasurface. By appropriately handling the ON/OFF states of the coding metasurface, we can control the reflected EM wave impinged on the metasurface. To verify the working ability of the coding metasurface, a prototype metasurface with a control board has been fabricated and measured. The results showed that the coding metasurface is capable of focusing beam to desired direction. For practical scenarios, we propose an adaptive optimal phase control scheme for focusing the beam to a mobile target. Furthermore, we prove that the proposed adaptive optimal phase control scheme outperforms the random phase control and beam synthesis schemes.

https://www.mdpi.com/1996-1073/12/23/4488/pdf

A Novel Coding Metasurface for Wireless Power Transfer Applications

We propose a battery-less location tracking system that enables 3-D positioning of an Internet of Things (IoT) device powered by the radio frequency (RF) wireless power transfer (WPT). In the proposed system, a power beacon is equipped with a phased antenna array that has the dual purposes of high-efficiency WPT and phase-based accurate positioning. In order to enhance the efficiency of the RF WPT, we propose a beam focusing algorithm that dynamically controls the respective phases of antenna elements to place the focal point of the electro-magnetic (EM) wave onto the target IoT device. We also propose a phase-based positioning algorithm that requires only one multiantenna anchor point for determining the distance as well as the direction from the anchor point. We analyze the Cramer–Rao lower bound (CRLB) of the phase-based positioning with a single multiantenna anchor point, and show that the distance from the anchor point can be estimated as long as the IoT device lies within the radiative near-field region. We propose a joint location tracking and WPT algorithm that performs 3-D positioning and beam-focused WPT in a unified way. We have built a real-life testbed with a large-scale antenna array with 64 antenna elements for testing the proposed algorithm. The experimental results show the effectiveness of the proposed algorithm in a real environment.

Battery-Less Location Tracking for Internet of Things: Simultaneous Wireless Power Transfer and Positioning

Recently, the fifth generation of cellular mobile communications (5G) network has been deployed and become pervasive. 5G offers a significant increase in terms of bandwidth and data rate compared to the previous generations. In addition, new technologies such as millimeter-wave (mmWave) technology and massive MIMO (mMIMO), have been proposed to meet the demand. However, some inevitable challenges still exist. In mmWave frequency, path loss and shadowing become more severe due to the radio electromagnetic (EM) wave characteristics. In this paper, we propose the utilization of reconfigurable intelligent surface (RIS) to aid wireless communications to overcome path loss and shadowing issues, by using a compressive sensing-based adaptive beamforming algorithm. To validate the theory, hypothesis, and simulation results, we have designed, fabricated, and conducted experiments with a 1-bit RIS testbed. The results show that the bit error rate (BER) and signal-to-noise ratio (SNR) of the received signal are significantly improved when the proposed RIS is employed. Further, we have also demonstrated a video streaming application aided by the proposed RIS as one of the potential RIS deployment scenarios.

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Reconfigurable Intelligent Surface-Aided Wireless Communications: Adaptive Beamforming and Experimental Validations

In this paper, we present a 5.8 GHz radio-frequency (RF) wireless power transfer (WPT) system that consists of 64 transmit antennas and 16 receive antennas. Unlike the inductive or resonant coupling-based near-field WPT, RF WPT has a great advantage in powering low-power internet of things (IoT) devices with its capability of long-range wireless power transfer. We also propose a beam scanning algorithm that can effectively transfer the power no matter whether the receiver is located in the radiative near-field zone or far-field zone. The proposed beam scanning algorithm is verified with a real-life WPT testbed implemented by ourselves. By experiments, we confirm that the implemented 5.8 GHz RF WPT system is able to transfer 3.67 mW at a distance of 25 meters with the proposed beam scanning algorithm. Moreover, the results show that the proposed algorithm can effectively cover radiative near-field region differently from the conventional scanning schemes which are designed under the assumption of the far-field WPT.

Nguyen Minh Tran

Papers

Distributed Wireless Power Transfer System for Internet of Things Devices

A Novel Coding Metasurface for Wireless Power Transfer Applications

Battery-Less Location Tracking for Internet of Things: Simultaneous Wireless Power Transfer and Positioning

Reconfigurable Intelligent Surface-Aided Wireless Communications: Adaptive Beamforming and Experimental Validations

Design and Implementation of 5.8GHz RF Wireless PowerTransfer System.