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Visible Light Communications

Visible Light Communications. Hoa Le Minh and Zabih Ghassemlooy Optical Communications Research Group (OCRG) School of Computing, Engineering and Information Sciences Northumbria University, United Kingdom hoa.le-minh@northumbria.ac.uk (ERASMUS Framework). Presentation Outline.

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Visible Light Communications

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  1. Visible Light Communications Hoa Le Minh and Zabih Ghassemlooy Optical Communications Research Group (OCRG) School of Computing, Engineering and Information Sciences Northumbria University, United Kingdom hoa.le-minh@northumbria.ac.uk (ERASMUS Framework)

  2. Presentation Outline • Optical wireless communications backgrounds • Visible Light Communications • Light Sources • Current technologies • Challenges • Organic Light Source • Summary

  3. Why Optical Wireless? RF spectrum: crowded, expensive OW spectrum: free, large bandwidth

  4. Optical Wireless Applications(short range) Traffic Communications Public data broadcasting Indoor broadband broadcasting in Hospital / Supermarket / University / Office Home Access Networks Military Communications

  5. Applications Probably the first ever applications in visible light communications Beam reflection (directional) Flame Source: Discovery Channel

  6. Network Evolution HFC Direct Fiber Ethernet MSO/ Cable Ethernet Ethernet Wireless [FSO/RF] SONET/ SDH Ethernet Bonded Copper Ethernet Carrier 1 TDM PON Carrier 2 Ethernet Bonded T1/E1 DS3/E3 Ethernet Source: NTT Ethernet 6 Ethernet High speed data delivered to home/office/premise  need ultrafast home access networks

  7. Apps: Home Access Network Power line, radio, visible light and infrared communications

  8. Home/Office Wireless Network • WiFi a/b/g/n – data rate R up to hundreds of Mbit/s • Bluetooth R ~ tens of Mbit/s • Optical wireless • Infra-red communications – R ~ Gbit/s • Visible light communications – R ~ hundreds of Mbit/s

  9. OW Apps: Broadband VLC Source: Boston University Indoor broadband broadcasting in Hospital / Supermarket / University / Office

  10. OW Apps: Indoor Broadband Source: Oxford University (OMEGA project)

  11. Apps: Traffic Communications FSO M Kavehrad PSU, USA

  12. Research in VLC VLCC (Casio, NEC, Panasonic Electric Works, Samsung, Sharp, Toshiba, NTT, Docomo) OMEGA (EU Framework 7) IEEE 802.15 Wireless Personal Area Network standards Boston University Siemens France Telecom Oxford University Edinburgh University Northumbria University

  13. VISIBLE LIGHT COMMUNICATIONS Main purpose: General Lighting Added Value: Communications

  14. General Lighting Sources • Incandescent bulb • First industrial light source • 5% light, 95% heat • Few thousand hours of life • Fluorescent lamp • White light • 25% light • 10,000s hours • Solid-state light emitting diode (LED) • Compact • 50% light • More than 50,000 hours lifespan

  15. 1.2 1 0.8 0.6 0.4 0.2 0 0.7 0.8 0.9 1.0 0.3 0.4 0.5 0.6 1.1 1.2 1.3 1.4 1.5 Light Source Spectrum Sun Incandescent Fluorescent Normalised power/unit wavelength UV IR Wavelength (m)

  16. What is LED?

  17. LED – Fundamental Light Emitting Diode (LED)

  18. White-Light LED • LED types: RGBBlue chip + PhosphorOLED New technology, expensive and short life time. It is, however, very potential Well-known technology, limited use, problem with balancing each R, G, B component to create white light Popular for today general lighting, efficient and cheap

  19. VLC System • Key Attributes • Secured communications: “you receive what you see” • Immunity to RF interference • Signals are easily confined • Unlicensed spectrum • Visible light meets eye-safe regulation • Green communications

  20. VLC System High Signal to Noise Ratio Signal to Noise ratio: how good signal is!

  21. VLC Transceivers DC current: for illumination (provide sufficient brightness) Signal: Data for communications

  22. LED Frequency Response LED frequency response LED temporal impulse response 100ns/div White light • Intrinsic LED modulation bandwidth is narrow (3MHz) • Blue-part provides wider bandwidth (20 MHz) 50ns/div Blue light

  23. How can we improve the LED frequency response?

  24. Pre-Equalisation Equalization BER performance VLC link configuration • 45 MHz equalized bandwidth achieved • 80 Mbit/s OOK-NRZ transmission

  25. Post-Equalisation Simple RC equalisation circuit Natural BW Equalised BW 3-time BW improvement

  26. Complex Modulation - Code Tx Rx 50 Msym/s 4-PAM Pulse Amplitude Modulation (PAM) Orthogonal Frequency-Division Multiplexing (OFDM) Orthogonal Subcarriers are used + M-QAM Likely achieved hundreds of Mbit/s

  27. Complex Modulation - Diversity Space Pulse Amplitude Modulation (SPAM)

  28. Cellular VLC Transmitter θa d1 φ Board with core r1 H Indoor channel receiver r2 receiver • User is highly mobile • Cellular structure and cell handover strategy are being developed • Cell size and transmit power are optimised

  29. High speed VLC • Summary of strategies to achieve high speed VLC (single channel) • Bandwidth expansion: equalisation • High bandwidth efficiency: complex modulation • - SNR and system dynamic range must be large to support both approaches

  30. Gigabit VLC If the channel matrix H is full rank, it is possible to transmit data in parallel Parallel transmission: Multiple-Input-Multiple-Output

  31. Tx1 Tx2 Tx3 Tx4 4Rx MIMO VLC Channel Matrix Issue: If there is a geometry symmetry rank(H) < 4

  32. MIMO VLC Performance Source: Oxford University (Samsung’s project)

  33. Organic LED (OLED)

  34. OLED • OLEDs: • Invented by Kodak in the 1980s • Intended for use in screens (brighter, thinner, faster, lighter and less power consumption than LCDs) • Produced in large panels that illuminate a broad area. • Can be flexible with the relevant plastic substrate (create different shape)

  35. OLED structure Source: Lumiblade

  36. OLED Electrical modelling (equivalent circuit) Lighting Large panel  better for illumination  larger capacitor value Communications Larger capacitor value  slow response Source: Lumiblade, Korea Institute of Industrial Technology

  37. OLED Equalisation approach Merit: total value of serial capacitors is smaller than individual capacitor value  The external Ceq minimises the effect of OLED capacitance OLED: experimentally transmit data at 2 Mbit/s over the original BW of 0.15 MHz

  38. Other Projects in VLC Smart VLC receiver and MIMO Portable device/Smartphone VLC Dimming and VLC

  39. Remaining Challenges Higher data rate? Uplink communications? Light dimming (asynchronous transmission)? Heat dissipation?

  40. Conclusions Optical Wireless Communications is an emerging technology that truly delivers data at very high rate with fibre-like quality

  41. Acknowledgements OCRG group School of CEIS Oxford University OMEGA project Samsung Electronics

  42. Thank you

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