Visible Light Communications

Theory and Applications

Zabih Ghassemlooy, Luis Nero Alves, Stanislav Zvanovec, Mohammad-Ali Khalighi, Zabih Ghassemlooy, Luis Nero Alves, Stanislav Zvanovec, Mohammad-Ali Khalighi

• Publisher: CRC Press
• Year: 2017
• eBook ISBN: 9781315350240
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Visible Light Communications, written by leading researchers, provides a comprehensive overview of theory, stimulation, design, implementation, and applications. The book is divided into two parts – the first devoted to the underlying theoretical concepts of the VLC and the second part covers VLC applications. Visible Light Communications is an emerging topic with multiple functionalities including data communication, indoor localization, 5G wireless communication networks, security, and small cell optimization. This concise book will be of valuable interest from beginners to researchers in the field.

1

Introduction

Zabih Ghassemlooy, Luis Nero Alves, Stanislav Zvánovec, and Mohammad-Ali Khalighi

CONTENT

1.1 State of the Art

In the past decade, the world has witnessed a dramatic increase in the traffic carried by the telecommunication networks. The increasing demand for high-speed Internet services (high-definition TV, video calls, and cloud-based computing) has underpinned the need for further innovation, research, and development in new emerging technologies capable of delivering ultra-high data rates to the end users. The existing radio frequency (RF) wireless spectrum is outstripping the supply, thus leading to spectrum congestion, which needs urgent attention. This is currently motivating what is known as the “tragedy of the commons” paradigm, a situation in which all users without any clear intention to do so will contribute to deplete a common resource, in this case, available spectrum. Such situations arise in high-density scenarios such as sport venues, concerts, airport, emergency situations, etc., where user demands may lead to the dramatic situation of limited access. Current RF-based communications suffer in particular from multipath propagation effects in dense urban environments, which reduce the link availability and its performance. The limited bandwidth of these systems together with the spectrum congestion means that relatively very few high-definition channels can be accommodated in a given area. This problem is more acute for indoor applications where there is a lack of adequate bandwidth to be shared among the large number of users who want a lion’s share of the channel capacity. It is estimated that more than 70% of the wireless traffic takes place in indoor environments (home, office, etc.). Therefore low-cost and highly reliable technologies are required to enable seamless indoor wireless communications. Squeezing more out of RF technologies or using an alternative such as optical technologies are the only two options available.

Regardless of the wireless technologies (i.e., 3G, 4G, 5G, and beyond) that are being adopted, there are only three approaches to increase the capacity of wireless radio systems: (i) release new spectrum and therefore more bandwidth; (ii) increase the number of nodes; and (iii) improve the spectral efficiency. Acquiring a new spectrum is costly, and finding more bandwidth is not a major problem but it is clearly not enough—it is finite. Adding more nodes is also being achieved via cell splitting, but this is rather costly and such systems also become too complex to manage. Also, two nodes do not offer twice the capacity of one, due to interference issues; the law of diminishing returns is at play. In addition, doubling the infrastructure will not lead to doubling the revenue. So in the long run, what are the solutions?

One possible alternative technology that can address and overcome these restrictions is optical wireless communications (OWCs), which utilizes infrared (IR), visible, and ultraviolet (UV) subbands, and remains mostly unexplored so far. Compared to RF, OWC offers superior features such as ultra-high bandwidth (in the order of THz), not being subject to electromagnetic interference, providing a high degree of spatial confinement bringing virtually unlimited frequency reuse, cost effectiveness with no licensing fee, and inherent physical security. With plenty of spectrum available, spectral efficiency is not as critical as in RF systems; nevertheless, most of the techniques developed for improving the spectral efficiency for RF systems can be applied to the optical domain. Whereas most of the proposed solutions for addressing the spectrum scarcity of RF systems consider scratching higher frequencies, such as millimeter and THz waves, with the major drawbacks of increased path loss and expensive transmitter/receiver components, OWC-based transmission systems draw their advantage due to the maturity of the transmission technology (therefore, relatively low-cost, high-performance components) as well as incomparable energy efficiency. The recent, yet well-known OWC in outdoor applications are the free-space optical (FSO) systems that operate at near IR frequencies (i.e., at wavelengths 750–1600 nm). These offer cost-effective and protocol-transparent links with high data rates (up to 10 Gbps per wavelength) and providing a potential solution for the backhaul bottleneck problem over short to long ranges up to a few kilometers.

OWC systems in the visible band (390–700 nm) are commonly referred to as visible light communications (VLCs), which take full advantage of visible light-emitting diodes (LEDs) for the dual purpose of illumination and data communications at very high speeds. VLC is a sustainable and green technology with the potential to revolutionize approaches to how we will use lights in the near future. It can provide solutions for a number of applications including wireless local area, personal area, and body area networks (WLAN, WPAN, and WBANs), heterogeneous networks, indoor localization and navigation (where current GPS is not available), vehicular networks, underground and underwater networks among others, offering a range of data rates from a few Mbps to 10 Gbps.

1.1 State of the Art

Factoring out molecular means of communications, which are part of all natural life on the planet, VLCs are perhaps the oldest means of communications known to humankind. Since the early days of human history, light has served as an essential means of communication. Possible examples are for instance the use of fire signals to communicate between tribes; use of reflected sunlight for ship-to-ship communications both utilized by ancient Greeks. For long-range communication, fire beacons placed on high points were lit from one point to another to deliver messages. Also, the ancient Chinese used smoke signals to communicate information on enemy movements between the army units along the Great Wall. Remarkably, VLC was proposed in more evolved technological society by Alexander Graham Bell with his photophone in 1880. This device was able to modulate sunlight with vibration caused by speech and transmitted the modulated light to an intended receiver. True advancements in VLC came with the discovery of electroluminescence and the LED in 1927, by the Russian scientist Oleg Losev. Coincidentally, Losev foresaw applications of his electroluminescence devices as communication devices. The story was quite different though. Wireless radio based on electromagnetic radiation has been established as the dominant communication technology over the last several decades. OWC based on IR light beams was originally proposed by Gfeller and Bapst in 1979. Their research work marked the beginning of the globally growing research activities, which has culminated in what we now recognize as OWC. Current research trends on OWC are focused on a range of different wavelengths from UV, through to the visible part of the spectrum and ending at the near IR regions of the spectrum. OWC offer unprecedented bandwidths, freedom from spectrum regulation, and inherently secure communications links, when compared to wireless RF systems. Among the research activities on OWC, one that is particularly attractive to be combined with the wireless RF systems to promote novel design concepts and techniques is VLC. VLC systems are currently attracting attention due to the growing use of LEDs for general lighting in a multitude of applications. With characteristics such as longer lifetime, better controllability, and energy efficiency, future lighting will definitely be based on LEDs replacing the conventional lighting devices on a worldwide scale. The unique characteristic of the LEDs is that they can be used at the same time for lighting and communications with unimaginable implications. This unique dual functionality of LEDs can be fully explored as a means to promote a truly green technology. When compared to FSO, most VLC systems are mainly based on diffuse radiation systems, where the presence of line of sight between terminal equipment is not mandatory. However, for high-speed applications, VLC with line-of-sight configurations can also be used. Current research trends have demonstrated the feasibility to achieve high data rate communications (links with data rates above 7 Gbps have been demonstrated) exploring this dual LED functionality. To achieve this performance landmark, several methods have been adopted to mitigate the slow response of power LEDs, for example, the use of optical discrete multitone modulations. Indeed, power LEDs used for lighting are driven with high forward currents when compared to IR LEDs and laser diodes, which makes them slower. Moreover, most power LEDs employ a yellow phosphorous coating to convert blue light into visible light, which further slows down the device response. Another interesting characteristic of VLC systems is their spatial confinement. When used in indoor scenarios, the communications range is limited by the room size, since no radiation crosses the walls. This makes these systems secure and potentially free from eavesdropping. Spatial confinement may also be explored in multiuser scenarios, where different light sources carry different data, but at the cost of increased system complexity.

The present book is composed of 16 chapters that cover a particularly wide scope of the theoretical and application-related aspects of VLC technology and address the different fundamental and practical considerations of these systems in different application scenarios. Along with 16 dedicated chapters, it provides comprehensive illustrations and performance analyses, without forgetting the future perspectives and technology deployment trends. It is an ideal reference for researchers who wish to initiate working on VLC-related research projects, or wish to deepen their knowledge of the field and gain insight into practical considerations. It is also an excellent reference textbook for graduate courses on the topic. Luis Nero Alves et al. in “Lighting and Communications: Devices and Systems” introduces the front-end devices and systems used for communication establishment in VLC systems. On the transmitter side, the focus is on LEDs which are exploited as both communication and lighting devices. The merger of lighting and communications means the same device builds up synergistic opportunities, but is not exempt from challenges. This chapter describes the challenges associated with the design of efficient LED drivers for future VLC systems. On the receiver side, the focus is on the use of photodiodes as the fundamental device for optical signal detection. Then follows a system overview of the most common techniques for optical amplifier design. The chapter ends with an overview of light regulations, something that is traditionally disregarded in VLC system specifications.

Zabih Ghassemlooy et al. in “Channel Modeling” consider this fundamental prerequisite step for the design of VLC links. Focusing on indoor systems, the chapter first introduces different sources of impairment arising from beam propagation or nonideal optoelectronic devices. Indeed, the latter can be considered as a part of the aggregate (i.e., global) communication channel. Then, different optical signal propagation modes are overviewed and the most relevant methods for numerical channel simulation are briefly explained. The authors then describe the limitations arising from the aggregate channel while focusing on the problem of intersymbol interference and how it can affect the link performance, as well as the signal distortion arising from the LED nonlinear characteristics. The chapter ends by addressing channel modeling for multiple-input multiple-output (MIMO) VLC systems. Tamás Cseh et al. in “Modulation Schemes” report on intensity modulation and direct detection (IM/DD)-based VLC systems. The chapter discusses baseband modulations including pulse-amplitude modulation, pulse-position modulations, pulse interval modulations, differential amplitude pulse-position modulation, variable pulse position modulation, and compare them in terms of power and bandwidth efficiencies, and peak-to-average power ratio. The chapter also describes multicarrier modulations (i.e., orthogonal frequency division multiplexing [OFDM] and its variants as well as pulse amplitude discrete multitoned, and the special modulation of color-shift keying.

Murat Uysal et al. in “IEEE 802.15.7: Visible Light Communication Standard” overview this standard, approved by IEEE in 2011, with a focus on the features of the physical and MAC layers. The chapter then provides simulation results to demonstrate the key performance metrics as well as the comparison of the different proposed physical layer schemes. Finally, the authors present the ongoing IEEE standardization activities and the most recent proposed amendments to the standard. Hoa Le Minh et al. in “Techniques for Enhancing the Performance of VLC Systems” start with the discussion of a technique for enhancing VLC system capacity. The chapter outlines parallel data transmissions (i.e., MIMO) using multiple LEDs, that are commonly used in home and office lighting, in order to increase channel capacity. In addition, the chapter discusses the OFDM scheme and outlines a viable scheme to overcome the problem of high peak-to-average power ratio. Also included is the dimming techniques adopted in high-speed VLC systems. Rafael Perez-Jimenez et al. in “VLC Applications for Visually Impaired People” provide descriptions of specific outdoor and indoor applications that can be employed in order to allow universal accessibility by disabled people. The chapter deals with both implementation using street lights as a resource for the mobility of blind people, and indoor positioning and guidance. It also presents a VLC-ultrasound hybrid solution and other specific applications for safety and emergency management tools.

Pengfei Luo et al. in “Car-to-Car Visible Light Communications” give an overview of the need for car-to-car communications as part of the intelligent transportation systems, where research and development, products, and standardizations are mostly focused around the RF-based communication technologies for wireless connectivity in vehicular networking. This chapter discusses the VLC technology inherent advantages over the RF-based dedicated short-range communication (DSRC) technology, as well as its key characteristics and features, which could be adopted for intelligent transportation system (ITS) applications. The chapter also outlines vehicular VLC communication models including both single-input single-output (SISO) and MIMO, noise sources, and road surface. Characterization of VLC-based car-to-car communications in terms of the link duration and channel time variation together the system performances and applications is also presented. In the next chapter “Visible Light Communications Based on Street Lighting,” Stanislav Zvanovec et al. discuss the main features of LED systems for public lighting systems especially in connection with VLC. Main functions, control systems, and typical parameters of street lighting are given. Furthermore, main aspects associated with lighting performance and aging are summarized. The chapter also outlines recent studies of public lighting-based VLC including ray-tracing simulations, noise parameters, and delay profiles among other topics. Luis Mauel Faria et al. in “Transdermal Optical Communications” discuss an interesting application of optical communications means to establish communications with implantable medical devices (IMDs), placed under the skin. The chapter presents and validates a channel model suitable for the design of communications systems employing optical communications means. The model is further explored to assess the possibility of building energy harvesting means using the same device used for optical signal detection. Conclusions indicate that it is possible to use optical means to communicate with IMDs. Both the skin depth and the radiation wavelength have a direct effect on the signal attenuation, thus revealing optical windows for communication.

Ali Khalighi et al. in “Underwater Visible Light Communications, Channel Modeling, and System Design” consider optical communication in underwater scenarios, which is among the most significant emerging applications. After presenting the fundamental aspects, the chapter provides a comprehensive description of the aquatic channel properties and modeling. Describing light beam propagation in water and the different processes that can affect it in an aquatic medium, the authors explain how these phenomena can be modeled mathematically and discuss channel characterization using analytical and numerical methods. Considerations in the design of the transmitter and the receiver are then addressed and the chapter ends with a description of the realization of a prototype together with some experimental evaluation results. Nuno Lourenço and Martin Siegel in “VLC for Indoor Positioning: An Industrial View on Applications” present an industrial vision of VLC-based positioning systems. Rather than being grounded in strong theoretical and experimental background, this chapter describes potential use cases for VLC systems. This is a corporate vision of one of the major key players in the field of lighting in Europe—Zumtobel. The key ideas discussed are linked to positioning systems based on VLC and their potential interest for lighting applications, ranging from light commissioning systems to position infotainment applications.

Michael B. Rahaim and Thomas D.C. Little in “Optical Small Cells, RF/VLC HetNets, and Software Defined VLC” provide very interesting descriptions and analyses of the application of VLC within next generation wireless RF/VLC networks. The chapter focuses on practical aspects of VLC utilization in the context of small cells, heterogeneous networks integration, and software-defined systems. It discusses a small cell evolution and utilization of VLC directionality for network densification within RF small cells such as femtocells or wireless local area networks. The chapter provides the requirements for coexistence of RF and VLC within mixed-media environments and describes a software defined VLC implementation in RF/VLC heterogeneous networks. Mónica Figueiredo and Carlos Ribeiro address the issue of an OFDM-based VLC system prototyping using reconfigurable hardware tools. Their chapter, entitled “OFDM-Based VLC Systems FPGA Prototyping,” presents the design flow for system design merging MATLAB^® system generator tools with Xilinx FPGA prototyping. A design example employing DCO-OFDM is used to illustrate the concepts and establish the link with the MATLAB user. Despite the simplicity of the approach, this methodology enables fast system development means, once the user is proficient with the tools used for prototyping.

Yeon Ho Chung in “Smart Color Cluster Indoor VLC Systems” presents the use of red, green, and blue (RGB) LEDs and color clustering to provide relatively high data rates and bidirectional transmission. Solutions supporting user mobility are also presented and multiple access schemes based on color coding are described to address multiuser scenarios. The considered solutions can ensure seamless coverage over various VLC-based connected devices present in a smart home environment, for example. Last, a method for the prospective application of indoor motion detection is described based on the use of multiple detectors. Finally, we cannot forget technologies which will form the majority of devices in near future, so the last chapter “VLC with Organic Photonic Components” by Paul Anthony Haigh et al. is focused on utilization of new organic technologies within VLC. This chapter gives an overview of organic-based VLC focusing on the organic LED (OLED)-based devices, the organic semiconductors, and visible light photodetectors. To enhance the OLED-based VLC links, a number of equalization schemes are discussed and their performances are compared. Finally, an experimental all-organic VLC system employing both OLED and organic photodetectors employing an artificial neural network–based equalizer is introduced and its performance evaluated.

2

Lighting and Communications: Devices and Systems

Luis Nero Alves, Luis Rodrigues, and José Luis Cura

CONTENTS

2.1 Introduction

2.1.1 Lighting Systems

2.2 Radiometry, Photometry, and ...

Table of contents

• Title Page
• Copyright Page
• Table of Contents
• Editors
• Contributors
• 1. Introduction
• 2. Lighting and Communications: Devices and Systems
• 3. Channel Modeling
• 4. Modulation Schemes
• 5. IEEE 802.15.7: Visible Light Communication Standard
• 6. Techniques for Enhancing the Performance of VLC Systems
• 7. VLC Applications for Visually Impaired People
• 8. Car-to-Car Visible Light Communications
• 9. Visible Light Communications Based on Street Lighting
• 10. Transdermal Optical Communications
• 11. Underwater Visible Light Communications, Channel Modeling and System Design
• 12. VLC for Indoor Positioning: An Industrial View on Applications
• 13. Optical Small Cells, RF/VLC HetNets, and Software Defined VLC
• 14. OFDM-Based VLC Systems FPGA Prototyping
• 15. Smart Color-Cluster Indoor VLC Systems
• 16. VLC with Organic Photonic Components
• Index