28-03-2012, 04:59 PM
An Introduction to VLC Technology
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Working with light
All forms of modern communication radio and television signals, telephone conversation and computer data rely on a carrier signal, a wavelike electromagnetic oscillation with a particular frequency. Electro-magnetic signals are described in terms of their wavelength (the distance between the peaks of two waves) or their frequency (expressed in hertz, the number of wave cycles per second); the shorter the wavelength, the higher the frequency. By modulating the carrier, we can encode the information to be transmitted; the higher the carrier frequency, the more information a signal can hold.
VLC Communication
Visible Light Communication has the potential for being an economical, secured solution to the last mile connectivity problem. LEDs in the bulbs apart from providing lighting can also be used for wireless communication and this can significantly improve security and capacity over fiber optic communication. The LED link is untethered and hence enables a communication link with many mobile devices like laptops and mobile phones. The link is untethered in the sense that a user is independent of any one host, and can get the same information at other optical hosts. Power Line Communications and Indoor Communications are two significant applications where the connectivity between the gadgets and the data providers cause bottleneck issues. VLC can thus play an important role along with other wireless technologies like Wi-Fi to address this problem.
History
Though the research and development of visible light communications systems was started not long ago (2003), man has always resorted to some form of communications employing a light source since Stone Age (Fig1.2.1). The age-old techniques of optical communication are listed in a chronological order:
Heliograph: In bygone times, reflecting mirrors were used to deliver information over a large distance. This technique is referred to as ‘Heliograph’.
VLC Characteristics
The merits and demerits of this technology become apparent once we go through the characteristics of visible light communication technology:-
• Human Safety: VLC poses no health hazards to human body. Thus, the transmission power can be kept high if needed.
• High Data Rates: VLC inherits high data rates from optical communications. Thus it can be used for very high speed wireless communications.
• Bandwidth: Visible light communications exploits the visible region of electromagnetic spectrum. Thus it offers much larger frequency band (300 THz) compared to that available in RF communications (300GHz).
• Ubiquitous Nature: We have a well-established lighting infrastructure throughout the world .In addition to it, LED based lighting devices are getting widespread acceptance round the globe. Since VLC uses the already available visible light sources for wireless communications, so it is expected to become a ubiquitous technology in near future.
• Security: As VLC involves line of sight communication, so it is impossible to tap the communication without breaking the link. So it offers a very secure communication and can be used in high security military areas where RF communication is prone to eavesdropping.
Applications of VLC
VLC is not meant for replacing existing wireless communication technologies; its sole purpose is to complement the existing wireless technologies.VLC offers a very wide area of research and applications. Some of the major applications are discussed briefly:
• Position Detector
• Intelligent Super market
• Intelligent Transport System
• Image Sensor Communications
• Networking
• Audio Applications
• Aesthetics
2.1 Position Detection
Different wireless technologies are being used for position detection in local and global navigation systems.VLC can also be used in such systems. Some of the popular technologies are discussed below followed by a comparison chart at the end (Fig 1.3.1).
2.1.1 Position Detection using GPS
In GPS (Global Positioning System), satellites are used to detect the position of a user. The user of GPS can know his/her position by receiving signals from at least 4 satellites (Fig 2.1). Although, it is the technology of choice for car navigation systems but it cannot be used in indoor environments.
VLC Research Centers
• Nakagawa Laboratories, Inc.
• Universal Traffic Management Society (UTMS)
• Smart Lighting ERC, Boston
• Rensselaer Polytechnic Institute
• OMEGA
• VLCC
• University of California, UC-Light Center
• Oxford University
• University of Edinburgh
• Fraunhofer Heinrich Hertz Institute
VLC Technology Market Key Players
• LVX Systems
• NEC Corporation
• Rise, Inc
• Gallium Lighting, LLC
• Sobal Corporation
• Outstanding Technology Co Ltd
• Casio Computer Co, Ltd.
• Intel Corporation