170007

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170007

  1. 1. Visible Light Communicationsand other developments in Optical Wireless Dominic O’Brien, University of Oxford, dominic.obrien@eng.ox.ac.uk Olivier Bouchet, France Telecom, olivier.bouchet@orange-ft.com Eun Tae Won, Samsung, etwon@samsung.com Dong Jae Shin, Samsung Contributions from Communications Group at Oxford
  2. 2. Overview • Optical wireless communications - Basics • Status of Optical Wireless (OW) in WWRF • New developments - Visible Light Communications - Infra-red - MIMO - IRDA update • Conclusions and future workWWRF page 2
  3. 3. Basic components: transmitter Source • LED or Laser diode Optics - Eye safety regulation means that high power requires sources to be modified - Three ranges - Visible (used for both illumination and data transmission) Output radiation - Near infrared 700nm>Wavelength<1400nm- Low cost Wavelength>1400nm- Eye safe • Arrays of sources also used - Used to provide multiple LOS paths, multiplexed transmissionWWRF page 3
  4. 4. Basic components: receiver • Receiver consists of - Optical filter - Rejects ‘out-of-band’ ambient illumination Input radiation noise - Lens system or concentrator Optical filter - Collects and focuses radiation Optical system - Photodetector (or array of detectors) Photodetector - Converts optical power to photocurrent Incoherent detection - Preamplifier (or number of preamplifiers) Amplifier - Determines system noise performance - Post-amplifier and subsequent processing OutputWWRF page 4
  5. 5. Optical wireless configurations • Basic configurations either use diffuse or Line-of-Sight (LOS) pathsWWRF page 5
  6. 6. System characteristics • Diffuse • Line-of-sight - Many paths from Transmitter to - Single path from Transmitter to Receiver Receiver - Robust to blocking - Low path loss Good coverage - No dispersion - High path loss Very high bandwidth available - Subject to multipath dispersion - Difficult to provide coverageWWRF page 6
  7. 7. Attributes of optical wireless • Advantages • Problems - Bandwidth - Incoherent detection - 200Thz carrier frequency - Less sensitive than radio - Security - Available components optimised - Wavelength allows directive links for fibre-optic applications using low cost ‘antenna’ (lenses) - Higher performance available if - Light confined by opaque barriers, optimised for OW so leakage not a problem - Link blocking - Interference - Geometrical solutions - Suitable for RF sensitive - Diffuse channels environments - Combine with RF - Potential for low power - Noise from ambient light - Optical filtering - Electrical filtering in receiverWWRF page 7
  8. 8. Status of Optical Wireless in WWRF • Whitepaper on OW for short-range communications complete - Book of visions 2006 • Opportunities - Short term - Point and shoot • Medium term - Augmentation of RF capacity - Optical hotspots - Similar in nature to 60GHz systems • Challenges - Improve link budget - Optimal integration into 4G infrastructure • Emerging areas - Visible light communicationsWWRF page 8
  9. 9. Visible light communications: background • Some work using fluorescent lights • Two emerging areas - Ilumination moving from incandescent/fluorescent to solid state sources (LEDs) - Predicted to become predominant method for room illumination - Used extensively in traffic systems (traffic signals,rear light cluster) - Headlight will be possible in future - Extra wireless capacity available at (potentially) low cost - Where visible light offers advantage over current methods - Point and shoot applications - Offers ‘intuitive’ alignmentWWRF page 9
  10. 10. VLC: Activity • Japanese consortium Visible Light Communications Consortium (VLCC)[1] - 21 members - Phase 1 complete-Low speed demonstrators - Phase 2 started-High speed communications • Research - Mostly in Japan (Keio University) • Commercialisation - Prototype systems [1] www.vlcc.netWWRF page 10
  11. 11. Introduction – Industry trend Mobile Illumination ITS PD White LED RGB LED [Max 10 Mbps) [Max 5 Kbps) [Max 5 Kbps) RGB Filter Ear phone Japan shop demo (Mar, 2006)WWRF page 11
  12. 12. VLC Sources • Blue LED & Phosphor • RGB triplet - Low cost - Higher cost - Phosphor limits bandwidth - Potentially higher bandwidth - Modulation can cause colour shift - Potential for WDM - Modulation without colour shift Single chip LED spectrum RGB LED spectrumWWRF page 12
  13. 13. VLC modellingWWRF page 13
  14. 14. Room Power Distribution • Assume - 1% modulation of typical illumination power - Typical receiver performance • Conclusions - Very high SNR available - SNRmin = 38.50dB - SNRmax = 49.41dB - Modulation limited by source bandwidthWWRF page 14
  15. 15. State of the art in VLC: Networking • Optical hotspot Connection to powerline ethernet VLC transmitter IR uplink High bandwidth Hotspot coverage area [1] Komine-T and Nakagawa-M, "Integrated system of white LED visible-light communication and power-line communication," IEEE Transactions on Consumer Electronics, vol. 49, pp. 71-9, 2003.WWRF page 15
  16. 16. State of the art in VLC • Short range ‘point and shoot’ - Intuitive alignment allows narrow beams - Improved power budget - Aesthetics [1] Ceatec. exhibition, "http://www.ceatec.com/en/2004/exhibitors/index.html."WWRF page 16
  17. 17. Feasibility at 4 Mb/s – PC-PC visible link 7mm diameter lensWWRF page 17
  18. 18. Music broadcast demonstrator 4x Transmitter modulated Luxeon Star LEDs ~5Mb/s link CD player Desklamp Receiver unit ReceiverWWRF page 18
  19. 19. Visible retro-reflecting transceiver • Light from reader strikes retro-reflecting tag - returned to the reader over a wide range of angles of incidence - Modulating the returned beam allows data to be transmitted from tag to reader Tag Reader • Tag has low power consumption as no source of radiation required • Long range Illuminating Beamsplitter Source θ Tag Receiver Retroreflecting Transceiver Reader showing angle of rotationWWRF page 19
  20. 20. Potential applications for VLC LED solid state lighting unit LED solid state lighting unit Line of sight optical link Visible Visible RF Wireless/optical optical link optical link channel Electronic PC or portable Noticeboard terminal Indoor Visible Light Communications Content retail terminal (DVD etc) Gb/s content exchange Gb/s content download Point to point Visible Light CommunicationsWWRF page 20
  21. 21. State of the art in VLC: telematics • Telematics • Applications - Visible signals used already - Traffic light-Car Communication [1] - Vehicle lighting moving to solid- - Car-Car communication via state sources - Headlights[2] Data communication - Headlight to tail light Data communication [1] Wook-Hbc, Haruyama-S, and Nakagawa-M, "Visible light communication with LED traffic lights using 2D image sensor," IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, vol. E89-A, pp. 654-9, 2006. [2] ISLE, "http://www.pb.izm.fraunhofer.de/p2sa/030_Projects/Optik/Pr_isle.html," 2006.WWRF page 21
  22. 22. New developments: IR • Infrared data association (IrDa) - 16Mb/s Very Fast IR (VFIR) products available - Standards being finalised for - IrBurst (100Mb/s) - UFIR (>100Mb/s)WWRF page 22
  23. 23. Improving the data rate: Optical MIMO • Measure Channel (H) matrix using training data • Measure data sequence • Process sequence to obtain estimate 1.5m 3x3 1x2 Laser sources photodiode array Schematic of experimentWWRF page 23
  24. 24. Recovered data • Processing - Threshold - Majority vote over bit period • No errors over 1.5m 1 1 0.9 0.9 Normalised signal level 0.8 0.8 0.7 0.7 0.6 0.6 0.5 0.5 0.4 0.4 0.3 0.3 0.2 0.2 0.1 0.1 0 0 2.5 3 3.5 4 4.5 5 5.5 6 2.6 2.8 3 3.2 3.4 3.6 3.8 4 time (s) x -6 -6 x 10 10 Data from source 1 Data from source 2WWRF page 24
  25. 25. Applications comparison Application Standard Telematics Networking Point to Point RF comms Intra-vehicle communications for Wide area coverage using IEEE Bluetooth <1Mb/s collision avoidance 802.11(g) Ultra-Wide Band 110/480 Mb/s Communications with infrastructure Bit rates up to 1Gb/s proposed for tolling Hotspot coverage using 60GHz systems-bit rates>1Gb/s High Power consumption ISO CALM standards under Complex systems required with line Complex modulation schemes and of sight RF propagation processing development IR Intra-vehicle communications for High bandwidth optical ‘hotspots’ Infra-red Data Association (IrDa) collision avoidance, Standards Communications with VFIR 16Mb/s (product) infrastructure for tolling IrBurst 100Mb/s(final vote) UFIR >100Mb/s (final vote) ‘Luciole’ optical link ~1.5Gb/s(JVC) ISO CALM standards under High modulation rates IR has good directivity Low power available Simple baseband transmission VLC Traffic light to vehicle comms. High bandwidth optical ‘hotspots’ Point to point links with improved link Intra-vehicle comms for collision margins compared to IrDa avoidance Visible light aids intuitive alignment Visible infrastructure already used High power available thus lowering link loss. for signalling Low modulation rates. Simple baseband transmissionWWRF page 25
  26. 26. Summary and Conclusions • Visible Light Communications - High SNR wireless channel - Intuitive communications • IR communications - MIMO techniques - Faster point and shoot • Challenges - Improve link budget - Integration into ‘4G’ wireless - Level (Network, MAC) - Low-cost systemsWWRF page 26

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