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 (ERASMUS Framework) “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

2 Presentation Outline Optical wireless communications backgrounds Visible Light Communications –Light Sources –Current technologies –Challenges Organic Light Source Summary “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

3 Why Optical Wireless? RF spectrum: crowded, expensive OW spectrum: free, large bandwidth “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

4 Optical Wireless Applications (short range) Traffic Communications Public data broadcasting Indoor broadband broadcasting in Hospital / Supermarket / University / Office Home Access Networks Military Communications “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

5 Applications Beam reflection (directional) Source: Discovery Channel Flame Probably the first ever applications in visible light communications “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

6 Network Evolution 6 Direct Fiber Source: NTT HFC DS3/E3 Bonded Copper Bonded T1/E1 Carrier 2 TDM SONET/ SDH PON Wireless [FSO/RF] Carrier 1 MSO/ Cable Ethernet High speed data delivered to home/office/premise  need ultrafast home access networks “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

7 Apps: Home Access Network Power line, radio, visible light and infrared communications “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

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 “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

9 OW Apps: Broadband VLC Indoor broadband broadcasting in Hospital / Supermarket / University / Office Source: Boston University “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

10 OW Apps: Indoor Broadband Source: Oxford University (OMEGA project) “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

11 Apps: Traffic Communications FSO M Kavehrad PSU, USA “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

12 Research in VLC VLCC (Casio, NEC, Panasonic Electric Works, Samsung, Sharp, Toshiba, NTT, Docomo) OMEGA (EU Framework 7) IEEE Wireless Personal Area Network standards Boston University Siemens France Telecom Oxford University Edinburgh University Northumbria University “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

13 VISIBLE LIGHT COMMUNICATIONS Main purpose: General Lighting Added Value: Communications “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

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 “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

15 Light Source Spectrum IRUV Wavelength (  m) Normalised power/unit wavelength Sun Fluorescent Incandescent “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

16 What is LED? “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

17 LED – Fundamental Light Emitting Diode (LED) “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

18 White-Light LED LED types: RGB Blue chip + Phosphor OLED 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 New technology, expensive and short life time. It is, however, very potential “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

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 “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

20 VLC System High Signal to Noise Ratio Signal to Noise ratio: how good signal is! “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

21 VLC Transceivers DC current: for illumination (provide sufficient brightness) Signal: Data for communications “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

22 LED Frequency Response LED frequency response Blue light LED temporal impulse response 100ns/div 50ns/div White light (1)Intrinsic LED modulation bandwidth is narrow (3MHz) (2)Blue-part provides wider bandwidth (20 MHz) “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

23 How can we improve the LED frequency response? “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

24 Pre-Equalisation 45 MHz equalized bandwidth achieved 80 Mbit/s OOK-NRZ transmission VLC link configuration Equalization BER performance “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

25 Post-Equalisation Simple RC equalisation circuit 3-time BW improvement Natural BW Equalised BW “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

26 Complex Modulation - Code Pulse Amplitude Modulation (PAM) Orthogonal Frequency-Division Multiplexing (OFDM) Orthogonal Subcarriers are used + M-QAM Likely achieved hundreds of Mbit/s Tx Rx 50 Msym/s 4-PAM “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

27 Complex Modulation - Diversity Space Pulse Amplitude Modulation (SPAM) “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

28 Cellular VLC Transmitter Board with core Indoor channel receiver d1 H r1 r2 θaθa φ receiver - User is highly mobile - Cellular structure and cell handover strategy are being developed - Cell size and transmit power are optimised “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

29 High speed VLC Summary of strategies to achieve high speed VLC (single channel) Pre- equalisation Post- equalisation Modulation scheme Modulation bandwidth Demonstrated data rate White channelOOK-NRZ2 MHz10 Mbit/s (BER < ) White channelxOOK-NRZ25 MHz40 Mbit/s (BER < ) Blue channelxOOK-NRZ45 MHz80 Mbit/s (BER < ) Blue channelxOOK-NRZ50 MHz100 Mbit/s (BER < ) Blue channelDMT-QAM25 MHz100 Mbit/s (BER < ) Blue channelDMT-QAM50 MHz231 Mbit/s (BER < ) - Bandwidth expansion: equalisation - High bandwidth efficiency: complex modulation - SNR and system dynamic range must be large to support both approaches “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

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 “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

31 MIMO VLC Channel Matrix Tx1Tx2Tx3Tx4 4  Rx Issue: If there is a geometry symmetry rank(H) < 4 “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

32 MIMO VLC Performance White channel White channel and equalisation Blue channel Number of channels Data rate (Mbit/s) Lens diameter (cm) Detector size (cm) 0.74x x x x x x x x x 31.4 Source: Oxford University (Samsung’s project) “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

33 Organic LED (OLED) “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

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) “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

35 OLED structure Source: Lumiblade “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

36 OLED Source: Lumiblade, Korea Institute of Industrial Technology Lighting Large panel  better for illumination  larger capacitor value Communications Larger capacitor value  slow response Electrical modelling (equivalent circuit) “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

37 OLED Equalisation approach Merit: total value of serial capacitors is smaller than individual capacitor value  The external C eq minimises the effect of OLED capacitance OLED: experimentally transmit data at 2 Mbit/s over the original BW of 0.15 MHz “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

38 Other Projects in VLC Smart VLC receiver and MIMO Portable device/Smartphone VLC Dimming and VLC “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

39 Remaining Challenges Higher data rate? Uplink communications? Light dimming (asynchronous transmission)? Heat dissipation? “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

40 Conclusions Optical Wireless Communications is an emerging technology that truly delivers data at very high rate with fibre-like quality “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

41 Acknowledgements OCRG group School of CEIS Oxford University OMEGA project Samsung Electronics “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011

42 Thank you “Gheorghe Asachi” Technical University of Iasi, Iasi, Romania, 13/06/2011