Hello All,
As editors of the problem statement, use cases & requirements draft we are
attempting to prepare a completed draft which could be ready for working
group last call before IETF83. In the coming days we will post the
sections of the draft to the mailing list. Our request is that you review
these sections and reply to the email with any comments.
Below is the text for sections 1 to 3. This text has not changed from
version-01 as uploaded October 31, 2011. Our goal is that any discussion
on this text will conclude by February 1. To be clear, approval of the
document will go through the normal process of last calls etc.. We are
simply asking for your assistance in preparing a complete & accurate
document that could progress the work. So please review the text and send
your comments either directly to the editor or to the mailing list.
Kind Regards,
Raj & Scott
1. Introduction
1.1. Introduction to TV white space
Wireless spectrum is a commodity that is regulated by governments.
The spectrum is used for various purposes, which include
entertainment (e.g. radio and television), communication (telephony
and Internet access), military (radars etc.) and, navigation
(satellite communication, GPS). Portions of the radio spectrum that
are allocated to a licensed, primary user but are unused or
unoccupied at specific locations and times are defined as "white
space". The concept of allowing secondary transmissions (licensed or
unlicensed) in white space is a technique to "unlock" existing
spectrum for new use. An obvious requirement is that these secondary
transmissions do not interfere with the primary use of the spectrum.
One interesting observation is that often, in a given physical
location, the primary user(s) may not be using the entire band
allocated to them. The available spectrum for a secondary use would
then depend on the location of the secondary user. The fundamental
issue is how to determine for a specific location and specific time,
if any of the primary spectrum is available for secondary use.
Academia and Industry have studied multiple cognitive radio
mechanisms for use in such a scenario. One simple mechanism is to
use a geospatial database that records the primary users occupation,
and require the secondary users to check the database prior to
selecting what part of the spectrum they use. Such databases could
be available on the Internet for query by secondary users.
Spectrum useable for data communications, especially wireless
Internet communications, is scarce. One area which has received much
attention globally is the TV white space: portions of the TV band
that are not used by broadcasters in a given area. In 2008 the
United States regulator (the FCC) took initial steps when they
published their first ruling on the use of TV white space, and then
followed it up with a final ruling in 2010 [FCC Ruling]. Finland
passed an Act in 2009 enabling testing of cognitive radio systems in
the TV white space. The ECC has completed Report 159 [ECC Report
159] containing requirements for operation of cognitive radio systems
in the TV white space. Ofcom published in 2004 their Spectrum
Framework Review [Spectrum Framework Review] and their Digital
Dividend Review [DDR] in 2005, and have followed up with a proposal
to access TV white space. More countries are expected to provide
access to their TV spectrum in similar ways. Any entity holding
spectrum that is not densely used may be asked to give it up in one
way or another for more intensive use. Providing a mechanism by
which secondary users share the spectrum with the primary user is
attractive in many bands in many countries.
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Television transmission until now has primarily been analog. The
switch to digital transmission has begun. As a result the spectrum
allocated for television transmission can now be more effectively
used. Unused channels and bands between channels can be used as long
as they do not interfere with the primary service for which that
channel is allocated. While urban areas tend to have dense usage of
spectrum and a number of TV channels, the same is not true in rural
and semi-urban areas. There can be a number of unused TV channels in
such areas that can be used for other services. The figure below
shows TV white space within the lower UHF band:
Avg |
usage| |-------------- White Space
| | | | | |
0.6| || || V V ||
| || ||| | ||
0.4| || |||| | ||
| || |||| | ||<----TV transmission
0.2| || |||| | ||
|----------------------------------------
400 500 600 700 800
Frequency in MHz ->
Figure 1: High level view of TV White Space
The fundamental issue is how to determine for a specific location and
specific time if any of the spectrum is available for secondary use.
There are two dimensions of use that may be interesting: space (the
area in which a secondary user would not interfere with a primary
user, and time: when the secondary use would not interfere with the
primary use. In this discussion, we consider the time element to be
relatively long term (hours in a day) rather than short term
(fractions of a second). Location in this discussion is geolocation:
where the transmitters (and sometimes receivers) are located relative
to one another. In operation, the database records the existing
user's transmitter (and some times receiver) locations along with
basic transmission characteristics such as antenna height, and
sometimes power. Using rules established by the regulator, the
database calculates an exclusion zone for each authorized primary
user, and attaches a time schedule to that use. The secondary user
queries the database with its location. The database intersects the
exclusion zones with the queried location, and returns the portion of
the spectrum not in any exclusion zone. Such methods of geospatial
database query to avoid interference have been shown to achieve
favorable results, and are thus the basis for rulings by the FCC and
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reports from ECC and Ofcom. In any country, the rules for which
primary entities are entitled to protection, how the exclusion zones
are calculated, and what the limits of use by secondary entities are
may vary. However, the fundamental notion of recording primary
users, calculating exclusion zones, querying by location and
returning available spectrum (and the schedule for that spectrum) are
common
This document includes the problem statement, use cases and
requirements associated with the use of white space spectrum by
secondary users via a database query protocol.
1.2. Scope
1.2.1. In Scope
This document applies only to communications required for basic
service in TV white space. The protocol will enable a white space
radio device to complete the following tasks:
1. Determine the relevant white space database to query.
2. Connect to the database using a well-defined access method.
3. Register with the database using a well-defined protocol.
4. Provide its geolocation and perhaps other data to the database
using a well-defined format for querying the database.
5. Receive in return a list of currently available white space using
a well-defined format for returning information.
As a result, some of the scenarios described in the following section
are out of scope for this specification (although they might be
addressed by future specifications).
1.2.2. Out of Scope
The following topics are out of scope for this specification:
TBD
2. Conventions and Terminology
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2.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2.2. Terminology
Database
In the context of white space and cognitive radio technologies,
the database is an entity which contains current information about
available spectrum at any given location and other types of
information.
Device ID
A unique number for each master device and slave device that
identifies the manufacturer, model number and serial number.
Location Based Service
An application or device which provides data, information or
service to a user based on their location.
Master Device
A device which queries the WS Database to find out the available
operating channels.
Protected Entity
A primary user of white space spectrum which is afforded
protection against interference by secondary users (white space
devices) for its use in a given area and time.
Protected Contour
The exclusion area for a Protected Entity, held in the database
and expressed as a polygon with geospatial points as the vertices.
Slave Device
A device which uses the spectrum made available by a master
device.
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TV White Space
TV white space refers specifically to radio spectrum which has
been allocated for TV broadcast, but is not occupied by a TV
broadcast, or other licensed user (such as a wireless microphone),
at a specific location and time.
White Space
Radio spectrum which has been allocated for some primary use, but
is not fully occupied by that primary use at a specific location
and time.
White Space Device (WSD)
A device which is a secondary user of some part of white space
spectrum. A white space device can be an access point, base
station, a portable device or similar. In this context, a white
space device is required to query a database with its location to
obtain information about available spectrum.
3. Prior Work
3.1. The concept of Cognitive Radio
A cognitive radio uses knowledge of the local radio environment to
dynamically adapt its own configuration and function properly in a
changing radio environment. Knowledge of the local radio environment
can come from various technology mechanisms including sensing
(attempting to ascertain primary users by listening for them within
the spectrum), location determination and internet connectivity to a
database to learn the details of the local radio environment. TV
White Space is one implementation of cognitive radio. Because a
cognitive radio adapts itself to the available spectrum in a manner
that prevents the creation of harmful interference, the spectrum can
be shared among different radio users.
3.2. Background information on white space in US
Television transmission in the United States has moved to the use of
digital signals as of June 12, 2009. Since June 13, 2009, all full-
power U.S. television stations have broadcast over-the-air signals in
digital only. An important benefit of the switch to all-digital
broadcasting is that it freed up parts of the valuable broadcast
spectrum. More information about the switch to digital transmission
is at : [DTV].
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With the switch to digital transmission for TV, the guard bands that
existed to protect the signals between stations can now be used for
other purposes. The FCC has made this spectrum available for
unlicensed use and this is generally referred to as white space.
Please see the details of the FCC ruling and regulations in [FCC
Ruling]. The spectrum can be used to provide wireless broadband as
an example. The term "Super-Wifi" is also used to describe this
spectrum and potential for providing wifi type of service.
3.3. Air Interfaces
Efforts are ongoing to specify air-interfaces for use in white space
spectrum. IEEEs 802.11af task group is currently working on one such
specification. IEEE 802.22 is another example. Other air interfaces
could be specified in the future such as LTE.
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