1. November 2008 Soo-Young Chang, CSUS Slide 1 doc.: IEEE 15-08-0790-00-0vlc SG-VLC Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: Some Technical Issues on VLC Date Submitted: November 2008 Source: Soo-Young Chang, CSUS Contact: Soo-Young Chang, CSUS Voice: E-Mail: sychang@ecs.csus.edu Re: Some technical issues on VLC Abstract: To discuss some technical issues on VLC, communication types and up and downlink categories related to these types are defined. Some relevant issues are introduced. Purpose: To Introduce some technical issues on visible light communications Notice:This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release:The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.

2. November 2008 Soo-Young Chang, CSUS Slide 2 doc.: IEEE 15-08-0790-00-0vlc SG-VLC Some Technical Issues on VLC Soo-Young Chang CSUS Nov. 2008

3. November 2008 Soo-Young Chang, CSUS Slide 3 doc.: IEEE 15-08-0790-00-0vlc SG-VLC Contents Types of Comm. Systems Multiplexing/Multiple Access Up/Down Link Categories Duplexing Multi-Hop VLC

4. November 2008 Soo-Young Chang, CSUS Slide 4 doc.: IEEE 15-08-0790-00-0vlc SG-VLC TYPES OF COMM SYSTEMS (1) A. Indoor short range (10m) 1.Infra & fixed/mobile, bidirectional, asymmetric, with illumination, PTP Downlink: 100 Mbps, uplink: 10 Mbps 2.Infra & fixed/mobile, bidirectional, asymmetric, with illumination, PTMP (broadcast) Downlink: 100 Mbps, uplink: 10 Mbps Multiple access required 3.Infra to fixed/mobile, unidirectional, with illumination, PTP or PTMP (broadcast): same contents to all receivers Downlink: 100 Mbps 4.Infra to fixed/mobile, unidirectional, with illumination, PTP or PTMP (broadcast): different content to each receiver Downlink: 100 Mbps 5.Mobile & fixed/mobile, bidirectional, symmetric, PTP Up/downlink: 100 Mbps 6.Mobile & fixed/mobile, unidirectional, PTP Downlink: 100 Mbps

5. November 2008 Soo-Young Chang, CSUS Slide 5 doc.: IEEE 15-08-0790-00-0vlc SG-VLC TYPES OF COMM SYSTEMS (2) B. Outdoor short range (10m) 1.Mobile-to-mobile, bidirectional, symmetric, PTP Up/downlink: 100 Mbps 2.Mobile-to-fixed, bidirectional, asymmetric, PTP Downlink: 100 Mbps, uplink: 100 Kbps 3.Mobile-to-mobile, unidirectional, PTP Up/downlink: 100 Mbps C. Outdoor short range (30m) 1.Mobile & display/sign board, bidirectional, asymmetric, PTP Downlink: 100 Mbps, uplink: 100 Kbps 2.Mobile-to-mobile, bidirectional, symmetric, PTP Up/downlink: 100 Kbps  Total 11 types of communications are defined to accommodate all applications so far identified.

6. November 2008 Soo-Young Chang, CSUS Slide 6 doc.: IEEE 15-08-0790-00-0vlc SG-VLC TYPES OF COMM SYSTEMS (3) Comm. type linkBi-/uni- direction symmetryIllumi /dimm PTP/PTMPData rateType no. Indoor short range (10 m) Between infra/base station/access point and mobile/fixed device Bi-asymmetricyesPTPDown: 100 Mbps Up: 10 Mbps A1 Bi-asymmetricyesPTMP /broadcast Down: 100 Mbps Up: 10 Mbps A2 Uni-yesPTP/PTMP /broadcast Down: 100 MbpsA3 Uni-YesPTP/PTMP /broadcast Down: 100 MbpsA4 Between mobile and fixed/mobile devices Bi-symmetricxPTPUp/Down: 100 Mbps A5 Uni-xPTPDown: 100 MbpsA6 Summary of VLC communication types

7. November 2008 Soo-Young Chang, CSUS Slide 7 doc.: IEEE 15-08-0790-00-0vlc SG-VLC TYPES OF COMM SYSTEMS (4) Comm. type linkBi-/uni- directio n symmetryIllumi /dimm PTP/PTMPData rateType no. Outdoor short range (10 m) Between mobile and mobile devices Bi-symmetricxPTPUp/Down: 100 Mbps B1 Between mobile and fixed devices Bi-asymmetricxPTPDown: 100 Mbps Up: 100 Kbps B2 Between mobile and mobile devices Uni-xPTPDown: 100 MbpsB3 Outdoor short range (30 m) Between mobile device and display/sign board Bi-asymmetricxPTPDown: 100 Mbps Up: 100 Kbps C1 Between mobile and mobile devices Bi-symmetricxPTPUp/Down: 100 Kbps C2 Summary of VLC communication types (cont’d)

8. November 2008 Soo-Young Chang, CSUS Slide 8 doc.: IEEE 15-08-0790-00-0vlc SG-VLC MULTIPLEX/MULTIPLE ACCESS (1) Multiplexing –For point-to-multipoint (PTMP) downlink, multiplexing needed –Conventional schemes: TDM and FDM Multiple access –For bidirectional PTMP uplink, a multiple access scheme needed –Conventional schemes: TDMA, FDMA, CDMA, etc. Duplexing –For bidirectional communications, duplex schemes needed to provide both direction communication links –Conventional schemes: TDD and FDD –In this document, full duplex is assumed. System design with these issues –For each comm. type defined, a system concept can be established. Multiplexing from an infra/base station/access point Multiple access from each unit/device for PTMP uplinks Duplexing between uplink and downlink

9. November 2008 Soo-Young Chang, CSUS Slide 9 doc.: IEEE 15-08-0790-00-0vlc SG-VLC MULTIPLEX/MULTIPLE ACCESS (2) Multiplexing –For point-to-multipoint (PTMP) communications, multiplexing needed –Using OFDM in this document Multiple access –For bidirectional uplink, multiple access schemes needed –Using OFDMA in this document Duplexing –For bidirectional communications, duplex schemes needed to provide both directional communication links –A few of possible schemes described in this document

10. November 2008 Soo-Young Chang, CSUS Slide 10 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (1) Various up/down link categories identified Links between an infra/base station/access point and a mobile/fixed device –Downlink PTMP  multiplexing : with illumination and possibly dimming control –Downlink PTP or broadcast  no multiplexing : with illumination and possibly dimming control –Uplink PTMP or (two-way) broadcast  multiple access –Uplink PTP  no multiple access Links between two mobile/fixed devices –Uplink and downlink PTP  no multiplexing, no multiple access

11. November 2008 Soo-Young Chang, CSUS Slide 11 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (2) Link typeUp/downPTP/PTMPMux/MAIllumi /dimm Categ ory no. Between infra/base station/access point and mobile/fixed device downPTMPMuxyesL1 downPTP or broadcast no MuxyesL2 upPTMP or broadcast MAxL3 upPTPno MAxL4 Between two mobile/fixed devices Up and down PTPno Mux /no MA xL5 Summary of categories of VLC links

12. November 2008 Soo-Young Chang, CSUS Slide 12 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (3) Transmitter and receiver configurations –Between an infra/base station/access point and a mobile/fixed –Between two mobile/fixed devices TxRx TxRx Infra/base station /access point Mobile/fixed Device 1 TxRxTxRx Mobile/fixed Device 2 Mobile/fixed Device n TxRx Mobile/fixed Device 1 TxRx Mobile/fixed Device 2

13. November 2008 Soo-Young Chang, CSUS Slide 13 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (4) Link Category L1: PTMP down link (transmitter) –MUX: Using OFDM Subset 1 Subset 2 Subset n IFFT Modulator n LED driverLED From information source Infra/base station/access point block diagram (transmitter)

14. November 2008 Soo-Young Chang, CSUS Slide 14 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (5) Link Category L1: PTMP down link (receiver) –MA: Using OFDMA Subset i FFT demodulator i amplifierPhoto detector to information sink Mobile/fixed device block diagram (receiver)

15. November 2008 Soo-Young Chang, CSUS Slide 15 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (6) Link Category L2: PTP or broadcast down link (transmitter) –No MUX: merely modulation using OFDM IFFT Modulator LED driverLED From information source Infra/base station/access point block diagram (transmitter)

16. November 2008 Soo-Young Chang, CSUS Slide 16 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (7) Link Category L2: PTP or broadcast down link (receiver) –No MUX: merely modulation using OFDM FFT demodulator amplifierPhoto detector to information sink Mobile/fixed device block diagram (receiver)

17. November 2008 Soo-Young Chang, CSUS Slide 17 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (8) Link Category L3: PTMP or broadcast uplink (transmitter) –MA: Using OFDMA Subset i IFFT Modulator i LED driverLED From information source Mobile/fixed device block diagram (transmitter)

18. November 2008 Soo-Young Chang, CSUS Slide 18 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (9) Link Category L3: PTMP or broadcast uplink (receiver) –MA: Using OFDMA Subset 1 Subset 2 Subset n FFT demodulator n amplifierPhoto detector to information sink Infra/base station/access point block diagram (receiver)

19. November 2008 Soo-Young Chang, CSUS Slide 19 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (10) Link Category L4: PTP uplink (transmitter) –No MA: Merely Modulation using OFDM IFFT Modulator LED driverLED From information source Mobile/fixed device block diagram (transmitter)

20. November 2008 Soo-Young Chang, CSUS Slide 20 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (11) Link Category L4: PTP uplink (receiver) –No MA: Merely Modulation using OFDM FFT demodulator amplifierPhoto detector to information sink Infra/base station/access point block diagram (receiver)

21. November 2008 Soo-Young Chang, CSUS Slide 21 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (12) Link Category L5: PTP uplink or downlink (transmitter) –No MA: Merely Modulation using OFDM IFFT Modulator LED driverLED From information source Mobile/fixed device block diagram (transmitter)

22. November 2008 Soo-Young Chang, CSUS Slide 22 doc.: IEEE 15-08-0790-00-0vlc SG-VLC UP/DOWN LINK CATEGORIES (13) Link Category L5: PTP uplink or downlink (receiver) –No MA: Merely Modulation using OFDM FFT demodulator amplifierPhoto detector to information sink Mobile/fixed device block diagram (receiver)

23. November 2008 Soo-Young Chang, CSUS Slide 23 doc.: IEEE 15-08-0790-00-0vlc SG-VLC DUPLEXING (1) Conventional duplex schemes for full duplex –TDD (Time Division Duplex) –FDD (Frequency Division Duplex) A couple of duplex schemes for VLC –Duplex 1: Using OFDM/OFDMA assumed A subset of frequency components for downlink Another subset of frequency components for uplink –Duplex 2: Direction Division Duplex (DDD) Using directional LEDs –Duplex 3: Code Division Duplex (CDD) Using orthogonal PN sequences

24. November 2008 Soo-Young Chang, CSUS Slide 24 doc.: IEEE 15-08-0790-00-0vlc SG-VLC DUPLEXING (2) Duplex 1: Orthogonal Frequency Division Duplex (OFDD) –If MUX/MA required: Using OFDM/OFDMA assumed A subset of frequency components for downlink to a single device or multiple devices Another subset of frequency components for uplink TxRx TxRx Infra/base station /access point Mobile/fixed Device 1 TxRxTxRx Mobile/fixed Device 2 Mobile/fixed Device n Downlink: Using subset i Uplink: Using subset j

25. November 2008 Soo-Young Chang, CSUS Slide 25 doc.: IEEE 15-08-0790-00-0vlc SG-VLC DUPLEXING (3) Duplex 2: (Direction Division Duplex, DDD) –Duplex: using isolation between uplink and downlink through directivity of transmitter and receiver LEDs LEDPD LEDPD Infra/base station /access point Mobile/fixed Device 1 LEDPDLEDPD Mobile/fixed Device 2 Mobile/fixed Device n Each LED has a small beam width.

26. November 2008 Soo-Young Chang, CSUS Slide 26 doc.: IEEE 15-08-0790-00-0vlc SG-VLC DUPLEXING (4) Duplex 2: (Direction Division Duplex, DDD) (cont’d) –For downlink, a broad beam is used to broadcast light signals while for uplink a narrower (pencil) beam is used to dedicate the signal to a specific receiver of a base station (or access point or infra). Transmitter Light source Infra system (base station, access point) User unit (mobile or fixed) Infra receiver Directed narrow beam

27. November 2008 Soo-Young Chang, CSUS Slide 27 doc.: IEEE 15-08-0790-00-0vlc SG-VLC DUPLEXING (5) Duplex 3: Code Division Duplex (CDD) –For downlink and uplink, different orthogonal PN sequences are assigned. For downlink: PN sequence i For uplink: PN sequence j for User Unit j –With this scheme, multiplexing and multiple access can also be achieved. Transmitter Light source Infra system (base station, access point) User unit(s) (mobile or fixed) Infra receiver PN sequence j used for uplink for User j PN sequence i used for downlink

28. November 2008 Soo-Young Chang, CSUS Slide 28 doc.: IEEE 15-08-0790-00-0vlc SG-VLC MULTI-HOP VLC (1) To cover broader area in indoor environment or to overcome short range problem –An in-building space is divided into multiple cells. –Each cell has its own base station (or access point). It is assumed that these base stations do not communicate with each other through an infra network. –To connect all base stations, some relays/repeaters are to be deployed to connect all base stations. –A mobile/fixed unit in a cell can communicate with a unit in another cell through a multiple hop connection.

29. November 2008 Soo-Young Chang, CSUS Slide 29 doc.: IEEE 15-08-0790-00-0vlc SG-VLC MULTI-HOP VLC (2) To cover broader area in indoor environment and to increase communication ranges –A server/gateway can be connected to only one base station. –Other base stations are connected with other base stations through multiple hop links.  small mesh network Base station Relay/repeater Server/ gateway Outside network

30. November 2008 Soo-Young Chang, CSUS Slide 30 doc.: IEEE 15-08-0790-00-0vlc SG-VLC MULTI-HOP VLC (3) Advantages with multi-hop VLC: Simple infrastructure to form a network among base stations Ubiquity can be easily realized. Quick deployment and flexible network configuration without additional infra networks. –For temporary events and places Easy installation for places where frequent configuration changes are required Short range can be overcome with multiple cells (or hops). Line-of-sight problem can be overcome with dynamic routing scheme. Abrupt blocking problem can be solved by switching routes – by changing to an alternative route. Slide 30

31. November 2008 Soo-Young Chang, CSUS Slide 31 doc.: IEEE 15-08-0790-00-0vlc SG-VLC SUMMARY VLC communication types are defined by reviewing applications suggested by all documents submitted so far. –11 comm. types All uplinks and downlinks are categorized for all comm. types defined. –5 links Multiplexing, multiple access, and duplexing for VLC are discussed. Multi-hop VLC for indoor environment is introduced to overcome some VLC problems. Slide 31