Communication at millimeter wave (mmWave) frequencies is defining a new era of wireless communication. The mmWave band offers higher bandwidth communication channels versus those presently used in commercial wireless systems. The applications of mmWave are immense: wireless local and personal area networks in the unlicensed band, 5G cellular systems, not to mention vehicular area networks, ad hoc networks, and wearables. Signal processing is critical for enabling the next generation of mmWave communication. Due to the use of large antenna arrays at the transmitter and receiver, combined with radio frequency and mixed signal power constraints, new multiple-input multiple-output (MIMO) communication signal processing techniques are needed. Because of the wide bandwidths, low complexity transceiver algorithms become important. There are opportunities to exploit techniques like compressed sensing for channel estimation and beamforming. This article provides an overview of signal processing challenges in mmWave wireless systems, with an emphasis on those faced by using MIMO communication at higher carrier frequencies.

An Overview of Signal Processing Techniques for Millimeter Wave MIMO Systems

In-band full-duplex (IBFD) operation has emerged as an attractive solution for increasing the throughput of wireless communication systems and networks. With IBFD, a wireless terminal is allowed to transmit and receive simultaneously in the same frequency band. This tutorial paper reviews the main concepts of IBFD wireless. One of the biggest practical impediments to IBFD operation is the presence of self-interference, i.e., the interference that the modem's transmitter causes to its own receiver. This tutorial surveys a wide range of IBFD self-interference mitigation techniques. Also discussed are numerous other research challenges and opportunities in the design and analysis of IBFD wireless systems.

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In-Band Full-Duplex Wireless: Challenges and Opportunities

In-band full-duplex (IBFD) operation has emerged as an attractive solution for increasing the throughput of wireless communication systems and networks. With IBFD, a wireless terminal is allowed to transmit and receive simultaneously in the same frequency band. This tutorial paper reviews the main concepts of IBFD wireless. Because one the biggest practical impediments to IBFD operation is the presence of self-interference, i.e., the interference caused by an IBFD node's own transmissions to its desired receptions, this tutorial surveys a wide range of IBFD self-interference mitigation techniques. Also discussed are numerous other research challenges and opportunities in the design and analysis of IBFD wireless systems.

Starting from Tesla's principles of wireless power transfer a century ago, this critical review outlines recent magneto-inductive research activities on wireless power transfer with the transmission distance greater than the transmitter coil dimension. It summarizes the operating principles of a range of wireless power research into 1) the maximum power transfer and 2) the maximum energy efficiency principles. The differences and the implications of these two approaches are explained in terms of their energy efficiency and transmission distance capabilities. The differences between the system energy efficiency and the transmission efficiency are also highlighted. The review covers the two-coil systems, the four-coil systems, the systems with relay resonators and the wireless domino-resonator systems. Related issues including human exposure issues and reduction of winding resistance are also addressed. The review suggests that the use of the maximum energy efficiency principle in the two-coil systems is suitable for short-range rather than mid-range applications, the use of the maximum power transfer principle in the four-coil systems is good for maximizing the transmission distance, but is under a restricted system energy efficiency (<;50%); the use of the maximum energy efficiency principle in relay or domino systems may offer a good compromise for good system energy efficiency and transmission distance on the condition that relay resonators can be placed between the power source and the load.

A Critical Review of Recent Progress in Mid-Range Wireless Power Transfer

Due to limitations of low power density, high cost, heavy weight, etc., the development and application of battery-powered devices are facing with unprecedented technical challenges. As a novel pattern of energization, the wireless power transfer (WPT) offers a band new way to the energy acquisition for electric-driven devices, thus alleviating the over-dependence on the battery. This paper presents an overview of WPT techniques with emphasis on working mechanisms, technical challenges, metamaterials, and classical applications. Focusing on WPT systems, this paper elaborates on current major research topics and discusses about future development trends. This novel energy transmission mechanism shows significant meanings on the pervasive application of renewable energies in our daily life.

Wireless Power Transfer—An Overview

This paper presents a maximum efficiency tracking control scheme for a closed-loop wireless power charging (WPC) system for wireless charging of mobile devices. Generally, wireless charging systems need a precise output voltage and current with the highest possible efficiency. In an open-loop system, output voltage and efficiency depend strongly on the coupling coefficient and load condition. Alternatively, a closed-loop WPC system has a constant output voltage against coupling and load variations. Many studies have been carried out regarding closed-loop systems. However, those previous studies have the drawback of efficiency degradation. In this paper, we propose a maximum efficiency tracking control scheme to achieve the highest possible efficiency. Therefore, the proposed WPC system satisfies both the requirements of a constant output voltage and high efficiency. The proposed control scheme determines the current of the transmitter based on the data received by the receiver via Bluetooth. For validation, the proposed WPC system was implemented at 6.78 MHz using loosely coupled series–series resonant coils, and we verified that the proposed system can track the maximum efficiency while maintaining a constant output voltage.

Design of Maximum Efficiency Tracking Control Scheme for Closed-Loop Wireless Power Charging System Employing Series Resonant Tank

A method for adjusting a beam pattern in a beam pattern adjusting apparatus in a communication system supporting a Beam Division Multiple Access (BDMA) scheme is provided. The method includes determining whether a Voltage Standing Wave Ratio (VSWR) value for each antenna included in an antenna array included in the beam pattern adjusting apparatus is greater than or equal to a threshold VSWR value, if it is determined that an antenna of the antenna array has a VSWR value that is greater than or equal to the threshold VSWR, detecting whether each of the antenna elements is operable, and if it is determined that at least one of the antennas is inoperable, adjusting a beam pattern of at least one of the antennas that is operable.

Apparatus and method for adjusting beam pattern in communication system supporting beam division multiple access scheme

Due to the convenience of using electronic devices, contactless energy transfer (CET) systems have garnered interest in various fields of industry. In this paper, a new design approach that uses antiparallel resonant loops for CET systems is presented. Forward and reverse loops forming an antiparallel resonant structure stabilize the transfer efficiency and therefore prevent it from dramatic distance-related changes, a phenomenon that can occur in CET systems with nonradiative methods (or resonant methods). This paper proposes frequency-insensitive antiparallel resonant loops and the optimal design of these loops for uniform transfer efficiency according to the distance. The proposed technique achieves frequency variation that is one-sixth that of conventional unidirectional loops, thus improving the power efficiency to a maximum of 87%. The improved performance of data transmissions for near-field communication is also verified.

Contactless Energy Transfer Systems Using Antiparallel Resonant Loops

A multiple band-notched planar monopole antenna for multiband wireless systems is presented. The proposed antenna consists of a wideband planar monopole antenna and the multiple U-shape slots, producing band-notched characteristics. In order to generate two band-notched characteristics, we propose that three U-shape slots are required. This technique is suitable for creating ultra-wideband (UWB) antenna with narrow frequency notches or for creating multiband antennas.

Multiple band-notched planar monopole antenna for multiband wireless systems

In this letter, a printable chipless tag with electromagnetic code using split ring resonators is proposed. A 4 b chipless tag that can be applied to paper/plastic-based items such as ID cards, tickets, banknotes and security documents is designed. The chipless tag generates distinct electromagnetic characteristics by various combinations of a split ring resonator. Furthermore, a reader system is proposed to digitize electromagnetic characteristics and convert chipless tag to electromagnetic code.

Jong-Won Yu

Papers

Design of Maximum Efficiency Tracking Control Scheme for Closed-Loop Wireless Power Charging System Employing Series Resonant Tank

Apparatus and method for adjusting beam pattern in communication system supporting beam division multiple access scheme

Contactless Energy Transfer Systems Using Antiparallel Resonant Loops

Multiple band-notched planar monopole antenna for multiband wireless systems

Design of Low-Cost Chipless System Using Printable Chipless Tag With Electromagnetic Code