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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

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

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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

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  1. 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. Some Technical Issues on VLC Soo-Young Chang CSUS Nov. 2008

  3. Contents • Types of Comm. Systems • Multiplexing/Multiple Access • Up/Down Link Categories • Duplexing • Multi-Hop VLC

  4. TYPES OF COMM SYSTEMS (1) A. Indoor short range (10m) • Infra & fixed/mobile, bidirectional, asymmetric, with illumination, PTP • Downlink: 100 Mbps, uplink: 10 Mbps • Infra & fixed/mobile, bidirectional, asymmetric, with illumination, PTMP (broadcast) • Downlink: 100 Mbps, uplink: 10 Mbps • Multiple access required • Infra to fixed/mobile, unidirectional, with illumination, PTP or PTMP (broadcast): same contents to all receivers • Downlink: 100 Mbps • Infra to fixed/mobile, unidirectional, with illumination, PTP or PTMP (broadcast): different content to each receiver • Downlink: 100 Mbps • Mobile & fixed/mobile, bidirectional, symmetric, PTP • Up/downlink: 100 Mbps • Mobile & fixed/mobile, unidirectional, PTP • Downlink: 100 Mbps

  5. TYPES OF COMM SYSTEMS (2) B. Outdoor short range (10m) • Mobile-to-mobile, bidirectional, symmetric, PTP • Up/downlink: 100 Mbps • Mobile-to-fixed, bidirectional, asymmetric, PTP • Downlink: 100 Mbps, uplink: 100 Kbps • Mobile-to-mobile, unidirectional, PTP • Up/downlink: 100 Mbps C. Outdoor short range (30m) • Mobile & display/sign board, bidirectional, asymmetric, PTP • Downlink: 100 Mbps, uplink: 100 Kbps • 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. TYPES OF COMM SYSTEMS (3) Summary of VLC communication types

  7. TYPES OF COMM SYSTEMS (4) Summary of VLC communication types (cont’d)

  8. 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. 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. 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. UP/DOWN LINK CATEGORIES (2) Summary of categories of VLC links

  12. 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 Infra/base station /access point Rx Tx Tx Rx Tx Rx Tx Rx Mobile/fixed Device 2 Mobile/fixed Device n Mobile/fixed Device 1 Mobile/fixed Device 1 Mobile/fixed Device 2 Tx Rx Tx Rx

  13. UP/DOWN LINK CATEGORIES (4) Link Category L1:PTMP down link (transmitter) • MUX: Using OFDM From information source Modulator n Subset 1 Subset 2 Subset n IFFT LED driver LED Infra/base station/access point block diagram (transmitter)

  14. UP/DOWN LINK CATEGORIES (5) Link Category L1:PTMP down link (receiver) • MA: Using OFDMA to information sink demodulator i Subset i FFT amplifier Photo detector Mobile/fixed device block diagram (receiver)

  15. UP/DOWN LINK CATEGORIES (6) Link Category L2:PTP or broadcast down link (transmitter) • No MUX: merely modulation using OFDM Modulator From information source IFFT LED driver LED Infra/base station/access point block diagram (transmitter)

  16. UP/DOWN LINK CATEGORIES (7) Link Category L2:PTP or broadcast down link (receiver) • No MUX: merely modulation using OFDM to information sink demodulator FFT amplifier Photo detector Mobile/fixed device block diagram (receiver)

  17. UP/DOWN LINK CATEGORIES (8) Link Category L3: PTMP or broadcast uplink (transmitter) • MA: Using OFDMA From information source Modulator i Subset i IFFT LED driver LED Mobile/fixed device block diagram (transmitter)

  18. UP/DOWN LINK CATEGORIES (9) Link Category L3: PTMP or broadcast uplink (receiver) • MA: Using OFDMA to information sink demodulator n Subset 1 Subset 2 Subset n FFT amplifier Photo detector Infra/base station/access point block diagram (receiver)

  19. UP/DOWN LINK CATEGORIES (10) Link Category L4: PTP uplink (transmitter) • No MA: Merely Modulation using OFDM From information source Modulator IFFT LED driver LED Mobile/fixed device block diagram (transmitter)

  20. UP/DOWN LINK CATEGORIES (11) Link Category L4: PTP uplink (receiver) • No MA: Merely Modulation using OFDM to information sink demodulator FFT amplifier Photo detector Infra/base station/access pointblock diagram (receiver)

  21. UP/DOWN LINK CATEGORIES (12) Link Category L5: PTP uplink or downlink (transmitter) • No MA: Merely Modulation using OFDM From information source Modulator IFFT LED driver LED Mobile/fixed device block diagram (transmitter)

  22. UP/DOWN LINK CATEGORIES (13) Link Category L5: PTP uplink or downlink (receiver) • No MA: Merely Modulation using OFDM to information sink demodulator FFT amplifier Photo detector Mobile/fixed deviceblock diagram (receiver)

  23. 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. 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 Infra/base station /access point Rx Tx Uplink: Using subset j Downlink: Using subset i Tx Rx Tx Rx Tx Rx Mobile/fixed Device 2 Mobile/fixed Device n Mobile/fixed Device 1

  25. DUPLEXING (3) • Duplex 2: (Direction Division Duplex, DDD) • Duplex: using isolation between uplink and downlink through directivity of transmitter and receiver LEDs Infra/base station /access point PD LED Each LED has a small beam width. LED PD LED PD LED PD Mobile/fixed Device 2 Mobile/fixed Device n Mobile/fixed Device 1

  26. 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). Infra system (base station, access point) Infra receiver Transmitter Light source Directed narrow beam User unit (mobile or fixed)

  27. 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. Infra system (base station, access point) Infra receiver Transmitter Light source PN sequence j used for uplink for User j PN sequence i used for downlink User unit(s) (mobile or fixed)

  28. 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. 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 Outside network Server/ gateway

  30. 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. 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

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