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

Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

Radiative wireless power transfer (WPT) is a promising technology to provide cost-effective and real-time power supplies to wireless devices. Although radiative WPT shares many similar characteristics with the extensively studied wireless information transfer or communication, they also differ significantly in terms of design objectives, transmitter/receiver architectures and hardware constraints, and so on. In this paper, we first give an overview on the various WPT technologies, the historical development of the radiative WPT technology and the main challenges in designing contemporary radiative WPT systems. Then, we focus on the state-of-the-art communication and signal processing techniques that can be applied to tackle these challenges. Topics discussed include energy harvester modeling, energy beamforming for WPT, channel acquisition, power region characterization in multi-user WPT, waveform design with linear and non-linear energy receiver model, safety and health issues of WPT, massive multiple-input multiple-output and millimeter wave enabled WPT, wireless charging control, and wireless power and communication systems co-design. We also point out directions that are promising for future research.

Communications and Signals Design for Wireless Power Transmission

https://calhoun.nps.edu/bitstream/10945/24839/1/singlesidebandtr00elli.pdf

Single sideband transmission by envelope elimination and restoration.

Radiative wireless power transfer (WPT) is a promising technology to provide cost-effective and real-time power supplies to wireless devices. Although radiative WPT shares many similar characteristics with the extensively studied wireless information transfer or communication, they also differ significantly in terms of design objectives, transmitter/receiver architectures and hardware constraints, etc. In this article, we first give an overview on the various WPT technologies, the historical development of the radiative WPT technology and the main challenges in designing contemporary radiative WPT systems. Then, we focus on discussing the new communication and signal processing techniques that can be applied to tackle these challenges. Topics discussed include energy harvester modeling, energy beamforming for WPT, channel acquisition, power region characterization in multi-user WPT, waveform design with linear and non-linear energy receiver model, safety and health issues of WPT, massive MIMO (multiple-input multiple-output) and millimeter wave (mmWave) enabled WPT, wireless charging control, and wireless power and communication systems co-design. We also point out directions that are promising for future research.

Wireless power transmission (WPT) is an emerging technology that is gaining increased visibility in recent years. Efficient WPT circuits, systems and strategies can address a large group of applications spanning from batteryless systems, battery-free sensors, passive RF identification, near-field communications, and many others. WPT is a fundamental enabling technology of the Internet of Things concept, as well as machine-to-machine communications, since it minimizes the use of batteries and eliminates wired power connections. WPT technology brings together RF and dc circuit and system designers with different backgrounds on circuit design, novel materials and applications, and regulatory issues, forming a cross disciplinary team in order to achieve an efficient transmission of power over the air interface. This paper aims to present WPT technology in an integrated way, addressing state-of-the-art and challenges, and to discuss future R&D perspectives summarizing recent activities in Europe.

Wireless Power Transmission: R&D Activities Within Europe

This paper presents the design and characterization of dc–dc converters operating at microwave frequencies. The converters are based on GaN transistor class-E power amplifiers (PAs) and rectifiers. Three topologies are presented, which are: 1) a PA and synchronous rectifier, requiring two RF inputs; 2) a PA and self-synchronous rectifier with a single RF input; and 3) a power oscillator with a self-synchronous rectifier with no required RF inputs. The synchronous 1.2-GHz class- ${\hbox{E}}^{2}$ converter reaches a maximum efficiency of 72% at 4.6 W. By replacing the RF input at the rectifier gate with a specific termination, a self-synchronous circuit demonstrates 75% efficiency at 4.6 W, with a maximum output power of 13 W at 58% efficiency. In the third topology, the PA is replaced by a power oscillator by providing correct feedback for class-E operation, resulting in a circuit requiring no RF inputs. This oscillating self-synchronous dc–dc converter is demonstrated at 900 MHz with an efficiency of 79% at 28 V and 12.8-W output power. Self-synchronous class-E transistor rectifier operation is analyzed theoretically in the time domain and validated with harmonic-balance simulations using an improved nonlinear model for a GaN HEMT. The simplified theoretical analysis provides a useful starting point for high-efficiency self-synchronous power rectifier design, which can, in turn, be extended to high-efficiency oscillating power inverter design.

/pdf/gan-microwave-dc-dc-converters-457m7bse2m.pdf

GaN Microwave DC–DC Converters

A simple retrodirective solution based on a heterodyne technique, without requiring a complex local oscillator (LO) distribution network, is presented in this paper. The system employs the TM20 mode of an orthogonal dual-feed square patch to receive a spatially distributed LO, containing the amplitude and phase components of the spectrally efficient wireless modulation format to be automatically retransmitted back to the interrogation position. The core of this solution is a phase conjugator, which employs the Envelope Elimination and Restoration (EER) principle, taking advantage oh the conversion gain modulation capability of drain-controlled active gate mixers. I. INTRODUCCIÓN Las agrupaciones retrodirectivas de antenas constituyen una solución prometedora para aplicaciones inalámbricas de bajo coste que precisan de una alta velocidad de respuesta, frente a los estructuralmente complejos y energéticamente ineficientes sistemas adaptativos, basados en engorrosos algoritmos de procesado digital de señales. En la solución heterodina propuesta por Pon en [1], la condición requerida para obtener un comportamiento retrodirectivo (la conjugación de fase), se logra seleccionado el producto más bajo de banda lateral resultante de la mezcla de la señal de interrogación con un oscilador local (OL) sintonizado al doble de su frecuencia. A pesar de las ventajas y la simplicidad que brinda esta técnica, su aplicación en los modernos sistemas inalámbricos aún es limitada, principalmente debido a los rigurosos requerimientos en términos de linealidad que presentan los modernos formatos de modulación multinivel y multiportadora, los cuales deben atravesar un proceso de conjugación de fase que es, intrínsecamente, no lineal. En varios trabajos se han tratado estos problemas. Por ejemplo, en [2] el mezclador conjugador de fase es simplemente sustituido por un detector de ángulo de arribo y un desfasador, mientras que en [3] se sugiere un sistema de modulación IQ modificado usando PLLs. En este trabajo se propone una solución similar a la presentada por los autores en [4], pero haciendo uso también del modo TM20 de una antena parche cuadrada, acoplada por dos ranuras ortogonales, con el objetivo de recibir una señal de OL espacialmente distribuida, que contiene la información de amplitud y fase de un formato de modulación espectralmente eficiente. Esta señal sería reenviada posteriormente en la dirección de interrogación. II. DESCRIPCIÓN GENERAL DEL SISTEMA En la Fig.1 se muestra un diagrama del sistema sugerido, integrando en su estructura el transpondedor propuesto. La señal de interrogación a 960 MHz con polarización vertical (PV) es recibida gracias al modo TM10 de cada parche alimentado ortogonalmente. La señal de OL a 1920 MHz es espacialmente distribuida con la misma polarización desde el foco del array, siendo en este caso recibida usando el modo TM20. Un diplexor permite separar ambas señales a puertos físicamente aislados. Inicialmente, un retardo adecuado es introducido entre los elementos (LO), como en una estructura reflectarray clásica [6]. Posteriormente, mientras se recibe la señal de interrogación a través del puerto INT, se le aplica una técnica de eliminación y restauración de envolvente (EER) [5] a la señal de OL. En [4], los autores demuestran la capacidad de modulación que presentan los mezcladores activos por puerta, con una ganancia de conversión muy lineal. Esto hace posible la recombinación de la envolvente compleja en los mezcladores. La señal de respuesta es retransmitida por el puerto RESP (modo TM10), usando polarización horizontal (PH) e incorporando la modulación digital deseada. Fig. 1. Diagrama del sistema retrodirectivo propuesto III. CONJUGADOR DE FASE EER En la Fig.2, se puede observar el núcleo del conjugador de fase propuesto: el mezclador activo por puerta. En la fotografía, los puertos correspondientes a las diferentes señales han sido marcados para que puedan ser identificados con claridad.

Conjugador de fase EER para sistemas retrodirectivos

ResumenIn this paper, a class E polar transmitter is presented, aimed to handle envelope-varying communication signals with high power efficiency. Implemented at UHF band, it combines a class E RF PA, excited by a phase modulated constant envelope signal, with a class E DC/DC converter, aimed to high-level and synchronously modulate the RF PA according to the amplitude component. Using GaN HEMT technology, both for the RF and the envelope power stages, and after applying digital predistortion (DPD), a global average efficiency over 40% is obtained for an EDGE signal.

Transmisor polar clase E³ en UHF sobre tecnología GaN HEMT

In this paper, highly efficient and linear wireless transmitting architectures are extended to retrodirective arrays (RDAs) for assuring full-duplex communications using spectrally efficient digital modulation formats. Dynamic biasing a single FET resistive mixer topology, or pumping two of them with properly outphased local oscillator excitations, the amplitude and phase components of the signal to be retransmitted may be recombined over an arriving interrogation with a different modulation format. Two 4x1 RDAs have been implemented, designed over dual-gate FET (DGFET) or Enhancement-mode PHEMT (EPHEMT) devices. Thanks to the incorporation of digital pre-distortion, the linear retrotransmission of a CDMA 2000 wireless signal is demonstrated.

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María de las Nieves Ruiz Lavín

Papers

Wireless Power Transmission: R&D Activities Within Europe

GaN Microwave DC–DC Converters

Conjugador de fase EER para sistemas retrodirectivos

Transmisor polar clase E³ en UHF sobre tecnología GaN HEMT

Sistemas retrodirectivos para la comunicación inalámbrica full-dúplex con alta eficiencia espectral