1. Feb. 2009
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: Some Thoughts on VLC: usage and implementation
Date Submitted: Feb 2009
Source: Rick Roberts, Praveen Gopalakrishnan Company: Intel Corporation
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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
Roberts and Gopalakrishnan, Intel

2. In the opinion of the authors …
Feb. 2009
In the opinion of the authors …
Of the many application usages proposed for VLC, the ones of most interest are those that enable new markets; that is, using VLC to do the same thing that is already being done with radio (e.g. WiFi) is NOT particularly interesting.
The applications of most interest leverage the unique properties of VLC such as inherent directionality (which enables localized services), the modulation of LED lighting of opportunity, or any complexity reduction advantage that VLC might have.
VLC is viewed as taking advantage of a signal source of opportunity. If an LED light has to be added to make the system work then that usage is probably NOT of interest.
Roberts and Gopalakrishnan, Intel

3. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
Feb. 2009
In the opinion of the authors (continued) …
Modulating LED sources of opportunity presents both technical and business challenges that will involve the cooperation of LED lighting vendors. The simpler the VLC modulation scheme the more likely the vendor will cooperate. Modulation schemes that require operation on the “linearized, small signal” portion of the LED operating curve might provide problematic for LED lighting vendors.
Modulating ITS devices (such as traffic lights and perhaps automobile lighting) will probably require regulatory support.
The reverse link for VLC can be very problematic for mobile devices, especially when modulating “LED lights of opportunity” (such as a light panel). The “transmit power” is highly asymmetrical with the downlink running watts of power and the uplink running milliwatts of power. For many applications involving mobile-to-infrastructure the link will, for all practical purposes, be uni-directional.
Roberts and Gopalakrishnan, Intel
<author>, <company>

4. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
Feb. 2009
In the opinion of the authors (continued) …
The applications of most interest to the authors - at this time - are those involving automobile networking and VLC embedded localized applications (e.g. smart signs/lights). A summary of our interest is shown below.
Vehicle to Vehicle
Vehicle to Infrastructure
Localized Services from Infrastructure
Environment
Outdoors
Indoors/Outdoors
Bi or Uni-directional
Bi-directional
Uni and Bi-directional
Uni-directional
Symmetric/Asymmetric Data
Symmetric
Asymmetric
Data Rate
~100 kbps
<10 Mbps
Distance
100 meters
10 meters
Source Intensity
High
Channel Type
LOS
Device Discovery/Beam Pointing
Automatic
Manual
Pt-to-Pt or WPAN
WPAN
Pt-to-MultiPoint and WPAN
Pt-to-MultiPoint
Centralized Controller No
Perhaps
Yes
Mobility
300 KPH
150 KPH
none
Roberts and Gopalakrishnan, Intel
<author>, <company>

5. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
Feb. 2009
In the opinion of the authors (continued) …
In regards to other usages outside our area of interest: we have no problem with the standard supporting all usages of general interest to the committee. Naturally we will be protective of those of most interest to us.
In regards to the MAC complexity to support widely varying data rates: normally the data rate spread supported by a MAC protocol should not exceed 10:1 because the low rate transmissions tie up the channel reducing the efficiency of the high rate transmissions. In VLC we have heard data rates that vary from 10 kbps to 100 Mbps … a 10,000:1 ratio. We suggest a method to circumvent this large ratio problem in the following bullet.
Roberts and Gopalakrishnan, Intel
<author>, <company>

6. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
Feb. 2009
In the opinion of the authors (continued) …
To accommodate the 10,000:1 data rate spread in VLC, we suggest specifying frequency sub-bands at the output of the photo-detector diode (similar to the suggestion in ).
Ambient Interference – not used for data
Spectrum out of the photodetector
10 kbps
to 100 kbps
100 kbps
to 1 Mbps
1 Mbps
to 10 Mbps
10 Mbps
to 100 Mbps
Hertz
There is a lot of detail missing, such as how to accommodate highly asymmetric data rates.
Roberts and Gopalakrishnan, Intel
<author>, <company>

7. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
Feb. 2009
In the opinion of the authors (continued) …
In regards to multiplexing multiple devices: it is believed SDM (spatial division multiplexing), in conjunction with FDM (frequency division multiplexing) and TDM (time division multiplexing), is appropriate. This may require certain applications to have sufficient optics as suggested in
Roberts and Gopalakrishnan, Intel
<author>, <company>

8. Traditional MAC managed only the time-frequency plane
Feb. 2009
The multiple device multiplexing options clarification:
Spatially separated devices can take advantage of SDM if spatially selective optics are available.
If SDM is not available (either the devices in question are spatially clustered together or the optics have a wide viewing angle) then if the devices are running significantly different data rates FDM can be used.
If SDM is not available and FDM is not available (because the devices in question are running similar data rates) then TDM can be used (the super frame can be partitioned and shared by multiple users).
Frequency
Traditional MAC managed only the time-frequency plane
Time
The VLC MAC needs to manage the time-frequency-spatial space
Space
Roberts and Gopalakrishnan, Intel

9. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
Feb. 2009
In the opinion of the authors (continued) …
In conjunction with the previous bullet, the MAC protocol needs to support automatic device discovery; that is, some use cases will require spatial scanning an image area to find the VLC source of interest (and perhaps also frequency sub-band scanning).
The protocol must support relatively high mobility; for example, two autos passing each other in opposite directions. We can assume the rate of closure to be as high as 300 KPH.
Roberts and Gopalakrishnan, Intel
<author>, <company>