第四章 Visible Light Communications.docx

第四章 Visible Light CommunicationsVLCn using LEDs for both illumination and data communications照明和通信 the increasing popularity of solid-state lighting固体照明 longer lifetime of high-brightness LEDs 寿命 high bandwidth/data rate带宽 data security数据安全 no health hazards健康 low power consumption功耗n interesting applications home networking high-speed data communication via lighting infrastructures in offices car-to-car communication high-speed communication in aeroplane cabins in-trains data communication traffic lights management and communicationsSolid-state lighting(SSL)n generated through solid-state electroluminescence电致发光n relatively short history n 1990s: the introduction of high-brightness LEDs for the purpose of general illuminationn LEDs luminous efficacy 100,000 hn organic LED (OLED): A new type source as an alternative solution for large area lighting and communicationsn SSL will be an imperative technology for significant energy savings and consequently a much greener worldAdvantages of LEDsn A longer life expectancyn A higher tolerance to humidityn Are mercury freen A smaller and compact sizen A much higher energy conversion efficiency (white LEDs 200 lm/W 425 lm/W Incandescent: 52lm/W; fluorescent: 90lm/W)n Minimum heat generation characteristics compared to all other lighting sourcesn Lower power consumptionn Most importantly, fast switchingLED Applicationsn Environment protection Kyoto Protocol : CO2 emission regulation RoHS : Hg-free bulbn Energy savingu Electricity in Korea 20% for Lighting : 55.6 TWh 50% saving by LED : 27.8TWhu Energy Saving Effect: 3 Nuclear Stations (1GW/day)；2 B$/yeaHistorical development of VLC2003first VLC started at Nakagawa Laboratory in Keio University, Japan2004Demonstration of LED light systems for high-speed transmission of data to hand-held and vehicle-borne computing devices; Japan2005Land trials of VLC communications to transmit information to mobile phones, with throughput estimated at 10 kbps and several Mbps using fluorescent light and an LED; Japan2007Demonstration of a LED-backlit liquid crystal display (LCD) television while transmitting information to a PDA via light; Fuji Television, Japan2007Visible Light Communications Consortium (VLCC) in Japan proposed two standards:Visible Light Communication System Standard Visible Light ID System Standard JEITA CP-1221 and JEITA CP-12222008Development of global standards for home networks, including the use of OWC employing IR and VLC technologies; European Union-funded OMEGA2008VLCC in Japan and the international Infrared Data Association (IrDA) working together on specification standards in the United States2009VLCC issued their first Specification Standard which incorporates and expands upon core IrDA specification and defined spectrum to allow for the use of visible light wavelengths2010Development of VLC technology for communications between a wide range of electronic products, such as high-definition televisions, information kiosks, personal computers, personal digital assistants smartphones and so on; University of California, USA2010Demonstration of VLC with the indoor global positioning system (GPS); Japan2010Transmission of an FM-VLED system at 500 Mbps over 5 m, Siemens and the Heinrich Hertz Institute, Germany2010Development a standard for VLC technologies by the IEEE Wireless Personal AreaNetworks working group 802 15 7 Task Group 7, which is ongoing (IEEE Std 802.15.7-2011)2011Demonstration of OFDM-based VLC at 124 Mbps real time, using commercial off-the-shelf phosphorescent white LED, University of Edinburgh, UKn data rates 40 Mbps: on-off keying technique n excess of 100 Mbps: with RGB white LEDs n Resonant cavity LEDs use Bragg reflectors, serving as mirrors, to enhance the emitted light 500 Mbpsn advanced modulation schemes (multilevel and multicarrier modulation techniques)n multiinput/multioutput techniqueDistinguishing featuresn Use of LEDs in cars, buses, aircrafts, trains, traffic lights and so on , in homes, offices and even in street lampsn SSL and indeed VLC can leverage on existing (local) power line and lighting infrastructures in offices, homes and so onn Transmitters and receiver devices, including multiarray/element devices are low costn It is safe, does not constitute or suffer from electromagnetic interference, and offers a huge unregulated bandwidth between 780 nm and 375 nmn VLC is relatively safe from potential eavesdroppersn ideal for hospitals, aircraft cabins, intrinsically safe environments like petrochemical industries and so onn Switching at ultrahigh speed (thousands of times per second), well beyond what the human eye can detect. No other lighting technology has this capabilityn The LEDs used in VLC are energy efficientApplications-Indoor application: LIFI Applications-outdoor application: ITSA sound communication system n Music sounds are transmitted through visible lights (RGB) independently. (i.e. R:Drum, G:Bass, B:Piano)n Music sounds can be controlled through their combination. （i.e. B:Piano only, R&G: Drum and Bass,White(RGB):Drum, Bass, Piano altogether)n Music sounds are transmitted through RGB lights (Each RGB light has a different sound; guittar, keyboard, etc.Visible light ID system (1)n Merchandise information distribution system; The product information is acquired by the visible light receiver on the shopping cartn The neighbor information distribution system from a traffic lightn Indoor Navigation System: Indoor Navigation Prototype for the Visually Impaired using Visible Light Communicationn Indoor Navigation Prototype for the Visually Impaired using Visible Light Communication: Indoor Navigation Prototype for the Visually Impaired using Visible Light CommunicationSystem DescriptionTransmitter device of VLCn Visible light LED up to several hundred Mbpsn Fluorescent lamp FSK modulation of high frequency fluorescent light；data rate: up to several kilo bpsReceiver device of VLCn PIN photo diode high speed reception up to 1Gbpsn Avalanche photo diode very sensitive receptionn Image sensor simultaneous image acquisition and data receptionPhosphorescent White LEDs RGB LEDsVLC技术的限制因素n Blue filtering at the receiver to filter out the slow-response yellowish componentsn Pre-equalization at the LED driving modulen Postequalization at the receivern Combination of the three above techniquesn Use of more complex modulation schemes where multiple bits can be carried by each transmitted symbol: QAM with optical OFDM, ect.n to hundreds of Mbpsn 白光LED有限的带宽限制了传输速率n 改进技术： 蓝光过滤 预均衡技术 后均衡技术 OFDM 波分复用（） 高阶