1. <month year>
doc.: IEEE
July 2009
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [VLC MAC considerations based on TCD]
Date Submitted: [16 July, 2009]
Source: [Ying Li, Sridhar Rajagopal, Farooq Khan, Taehan Bae, Jaeseung Son, Eun Tae Won] Company [Samsung Electronics]
Address [1301 E. Lookout Drive, Richardson, TX 75082, USA]
Voice:[ ], FAX: [ ], [
Re: []
Abstract: [MAC design considerations for VLC are discussed.]
Purpose: [Contribution to IEEE VLC TG]
Notice: This document has been prepared to assist the IEEE P 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 P
Ying Li, Samsung Electronics
<author>, <company>

2. Samsung MAC considerations based on TCD
July 2009
Samsung MAC considerations based on TCD
Application focus
Indoor/Outdoor
Infrastructure/Mobile
Mbps
Multiple topologies (Peer to peer/star)
Mobility
Uni/bi-directional/broadcast data transfer
Ying Li, Samsung Electronics

3. Focus for presentation
July 2009
Focus for presentation
Band plan
Guard colors
Device discovery and capabilities
MAC PDU types for data, dimming/visibility support
Dimming support
Rate adaptation
Resource allocation
Ying Li, Samsung Electronics

4. Band plan design for communicating supported channels
July 2009
Band plan design for communicating supported channels
Source:
Ying Li, Samsung Electronics

5. July 2009
Notes from CIE diagram
Center colors are narrower in width than outer colors.
Human eye is more sensitive to center colors
pB, R occupy 100~200 nm while G occupies ~ 30 nm
LED manufacturers make LEDs depending on human color perception and not frequency band
=> Non-linear widths needed for band plan
Ying Li, Samsung Electronics

6. Human eye response to wavelength
July 2009
Human eye response to wavelength
Ying Li, Samsung Electronics

7. Proposed Band Plan (based on CIE diagram)
July 2009
Proposed Band Plan (based on CIE diagram)
Frequency band (nm)
Spectral width (nm)
Color
Proposed Code
380
450 70 pB
000
510 60
B, BG
001
560 50 G
010
600 40
yG,gY, Y,yO,O
011
650 rO
100
710 R
101
780
110
Reserved
111
Red – popular
LED for comm.
Non-uniform distribution based on CIE diagram
Human eye most sensitive to green color and visible LEDs are designed to match human eye sensitivity
Provides support for up to 7 independent and parallel channels – can consider expansion to more channels
Ying Li, Samsung Electronics

8. Bandplan issue: Leakage from other LED colors
July 2009
Bandplan issue: Leakage from other LED colors
Source:
Ying Li, Samsung Electronics

9. White LED spectrum (Blue + Phosphor)
July 2009
White LED spectrum (Blue + Phosphor)
Blue LED
(GaInN)
Light sensitivity to human eye
Yellow Phosphor
yttrium aluminum garnet
(YAG) –
leakage if not used at RX
Source: Maxim, Application Note 3070 : Standard and White LED Basics and Operation
Ying Li, Samsung Electronics

10. July 2009
Need for guard colors
Many LEDs (such as white) may not support saturated colors and may transmit in multiple bands
Spectrum affected by leakage may be unusable
For FDD mode, adjacent bands may be impacted by spectral leakage from own transmitter
Significant variations in LED spectral width and peak wavelengths for different manufacturers and costs
LED peak wavelength can change with forward current variations.
Ying Li, Samsung Electronics

11. July 2009
Guard colors
We define “guard color” channels for each channel used for transmissions.
For every channel color, we define a list of guard colors that cannot be used simultaneously for TX or RX when that channel is in use for TX due to leakage.
For example, white led (blue + phosphor) Color code : 001 Guard codes : 011, 100
The criteria used for defining a guard color channel could be based on out-of-band leakage, exceeding a certain value (for example, dB) over the in-channel value that causes a considerable loss in receiver sensitivity in those channels.
The guard colors are defined on a per channel basis and could be also be defined as a N-bit number with a ‘1’ in the location where the channel cannot be used.
Example: Guard colors (011,100) for 001 can be represented as:
Ying Li, Samsung Electronics

12. July 2009
Exchanging capabilities and channel selection during device discovery process
Device 1 (host/master)
Device 2
Transmit on M1 channels
Send channel colors supported, guard channels, application requirements
Exchange capabilities
Device 1 – M1 colors
Device 2 - M2 colors
K = M1 ∩ M2 – common colors
CQI – Color Quality Indicator report
Transmit on K channels
Send channel colors supported, guard channels, application requirements
Send RX CQI report for K channels
Send TX CQI report for K channels
Channel selection
Inform channel(s) used for TX and RX and access (TDD/FDD)
Data transfer on agreed channel(s)
Ying Li, Samsung Electronics

13. Capabilities Information Element for device discovery
July 2009
Capabilities Information Element for device discovery
PHY capabilities:
Colors supported
Data rates
Guard colors for each supported color
MAC capabilities:
Uni-directional traffic support
Bi-directional traffic support
P2P support
P2MP support
Dimming support
Visibility support
Ying Li, Samsung Electronics

14. Two types of MAC PDU MAC packet data unit (PDU)
July 2009
Two types of MAC PDU
MAC packet data unit (PDU)
Regular PDU, for Data/Signaling
Padding PDU, for Visibility support
The padding PDUs can be used for other purposes, such as the channel quality measurement.
Ying Li, Samsung Electronics

15. Visibility/Dimming Support
July 2009
Visibility support
Visibility of the beam can be used to assist pointing and device alignment
Addition to VLC data/signaling, visibility padding can be used to support the visibility
The pattern of visibility support can be adaptive so that the blinking can be an indicator of the link quality
Dimming support
Infrastructure may have dimmers
Dimming padding duty cycle should match up the dimmer requirements
Visibility padding can be treated as a special case of dimming padding
Ying Li, Samsung Electronics

16. Infrastructure VLC Device
VLC when Dimming
July 2009
Dimming cycle patterns of infrastructure should be notified to VLC RX device, so that the VLC device could adapt to the dimming pattern
Infrastructure VLC may receive a dimming request from a dimmer triggered by user
Propose to use a link adaptation timer that delays the time between the dimming request and the actual dimming of the light source.
With this knowledge of an incoming dimming, the link between the devices can be adapted to work at a new (lower) data rate (if dimmed) without requiring the link to be interrupted or possible link failure.
Infrastructure VLC Device
VLC Device
User
Dimmer
Link adaptation and communication
Dim light
Dimming request
Dimming pattern.
Updated scheduling & resource allocation due to dimming
Link adaptation timer
Uninterrupted communication with adapted link
Actual dimming
Ying Li, Samsung Electronics

17. Rate Control/Adaptation
July 2009
Rate Control/Adaptation
To maximize the throughput and to provide the flexibility of transmission rate, the transmission rate control is needed.
The transmission rate is adaptively adjusted according to the channel quality.
Schemes to support rate control
The data rate supported can be indicated, e.g., in the frame header
The transmission rate can be estimated from the channel quality which can be measured/estimated by, e.g.,
the preambles used for synchronization
the padding for the visibility/dimming
Ying Li, Samsung Electronics

18. QoS provision: Resource Allocation for Various Traffic
July 2009
QoS provision: Resource Allocation for Various Traffic
Schemes for resource request
Real-time, fixed size: use pre-allocated resource
Real-time, variable size data: use real-time polling, periodically
Non real-time with different priorities: use non-real-time polling, regularly, even during congestion.
Best effort data: if there is no polling resource available, use contention based resource request.
Ying Li, Samsung Electronics

19. July 2009
Summary
Band plan supporting 7 independent color channels proposed (can consider more channels)
Guard colors proposed for interference mitigation due to leakage
Two MAC PDU types defined for data and visibility/dimming
Link adaptation notification and timer for dimming
Ying Li, Samsung Electronics