Visible Light Communication (VLC) is an emerging field in Optical Wireless Communication (OWC) which utilizes the superior modulation bandwidth of Light Emitting Diodes (LEDs) to transmit data. In modern day communication systems, the most popular frequency band is Radio Frequency (RF) mainly due to little interference and good coverage. However, the rapidly dwindling RF spectrum along with increasing wireless network traffic has substantiated the need for greater bandwidth and spectral relief. By combining illumination and communication, VLC provides ubiquitous communication while addressing the shortfalls and limitations of RF communication. This paper provides a comprehensive survey on VLC with an emphasis on challenges faced in indoor applications over the period 1979–2014. VLC is compared with infrared (IR) and RF systems and the necessity for using this beneficial technology in communication systems is justified. The advantages of LEDs compared to traditional lighting technologies are discussed and comparison is done between different types of LEDs currently available. Modulation schemes and dimming techniques for indoor VLC are discussed in detail. Methods needed to improve VLC system performance such as filtering, equalization, compensation, and beamforming are also presented. The recent progress made by various research groups in this field is discussed along with the possible applications of this technology. Finally, the limitations of VLC as well as the probable future directions are presented.

As a new generation green lighting source, the light emitting diode (LED) is rapidly replacing traditional incandescent and fluorescent light sources. Apart from providing energy savings, the use of LED lighting technology creates scope for an innovative optical wireless communication technology known as visible light communication (VLC), which takes advantage of the superior modulation capability of LEDs to transmit data through a wireless channel. VLC is capable of concurrently providing communication as well as illumination. For making commercial implementation of VLC feasible, it is necessary to incorporate it with dimming schemes that will provide energy savings, moods, and increase the aesthetic value of the place using this technology. However, general dimming techniques have an adverse effect on communication since they limit the achievable data rate of a VLC link. This drives the necessity of formulating efficient dimming techniques, which will create a balance between the two most basic functions of VLC: illumination and communication. This paper focuses on dimming mechanisms that can be implemented in VLC systems to save energy and provide precise illumination control. The motivation behind this control mechanism, current challenges in practical implementation, driver circuitry, recent progress, and future prospects are also concisely presented.

Q-factor constraints are usually imposed on conductor loops employed as proximity range High Frequency Radio Frequency Identification (HF-RFID) reader antennas to ensure adequate data bandwidth. However, pairing such low Q-factor loops in inductive energy transmission links restricts the link transmission performance. The contribution of this paper is to assess the improvement that is reached with a two-stage design method, concerning the transmission performance of a planar square loop relative to an initial design, without compromise to a Q-factor constraint. The first stage of the synthesis flow is analytical in approach, and determines the number and spacing of turns by which coupling between similar paired square loops can be enhanced with low deviation from the Q-factor limit presented by an initial design. The second stage applies full-wave electromagnetic simulations to determine more appropriate turn spacing and widths to match the Q-factor constraint, and achieve improved coupling relative to the initial design. Evaluating the design method in a test scenario yielded a more than 5% increase in link transmission efficiency, as well as an improvement in the link fractional bandwidth by more than 3%, without violating the loop Q-factor limit. These transmission performance enhancements are indicative of a potential for modifying proximity HF-RFID reader antennas for efficient inductive energy transfer and data telemetry links.

This Letter describes a simple compensation method to reduce the transfer efficiency variation in a resonant inductive coupling (RIC) wireless power transfer link subject to lateral misalignment. The technique is based on impedance matching an RIC link such that the link operates at either over-coupling or critical coupling within the extents of lateral misalignment. Applying the method in a test scenario led to a reduction in the range of obtained transfer efficiency values, from 45% of peak value in a conventional arrangement, to 5%. The proposed method has a potential for application in the design of free-positioning planar wireless chargers.

The elimination of physical conductors as media for power transmission is an important step towards reducing the bulk of waste material generated when electronic gadgets are disposed of. In addition, the increasing deployment of low-power autonomous electronics in less accessible environments has provided an impetus for the development of wireless energy transfer alternatives to wired power delivery. This paper presents a review of near-field magnetic wireless energy transfer link architectures, and design approaches for realizing performance objectives specifically suited to low-power deployments. First, the paper provides a brief history of low-power magnetic wireless energy transfer development. This is followed by a fundamental description of the spatial regions surrounding an electromagnetic field source. Then, the paper presents a summary of basic topologies of magnetic wireless energy transfer link implementations, while emphasizing their distinctive features. Design approaches, which enable the realization of various link performance criteria, are also discussed. Finally, this paper highlights emergent wireless energy transfer link design trends inspired by communication network paradigms.

The low Q-factor requirements of High-Frequency Radio Frequency Identification (HF-RFID) interrogator antennas constrain transmission performance when they are used in data links requiring similar terminal antennas. This letter presents a geometrical approach to enhance the transmission performance of planar loop antennas without a significant change to their standalone performance as HF-RFID interrogator antennas. The method distributes the turns of a modified planar square loop antenna to enhance the coupling level in a symmetric link, while limiting the change in Q-factor from a conventional HF-RFID interrogator antenna. Results from a presented test case show that the design method enables a 5.75% increase in peak transmission coefficient, and a 28.42% fractional bandwidth increase in a symmetric link, compared to a conventional design.

The transfer efficiency of two-coil resonant inductive power transfer links is known to significantly degrade with a reduction of the coil distance, due to an over-coupling at shorter distances. In this work, a simple technique is introduced to determine the spatial layout of reverse-current coil turns, which suppresses the overcoupling- induced transfer efficiency drop. By employing the spatial layout of reverse-current turns as a design parameter, the proposed method provides more generality in its implementation compared to other reverse-current turn methods. Simulation and experimental results validate the method, suggesting a potential for distanceinsensitive implementations.

A compact proximity coupled high harmonic rejection filtenna is presented in this paper. The proposed structure operates in the unlicensed 2.45GHz Industrial, Scientific and Medical (ISM) band. A circular ring slot has been built-in on the ground plane parallel to circular patch, resulting in a 45% reduction area of patch element area as compared to conventional designs. Unique U-shaped slot arrangements are created on the ground plane parallel to the transmission line feed as defected ground structures (DGS) to achieve rejection of higher harmonics. Acceptable suppression of the second and third harmonics is achieved with minimum reflection coefficients of ™4.1 dB and ™1.8 dB respectively. The proposed design shows good potential for implementation in wireless power transfer and radio frequency energy harvesting infrastructure.