Individual Submission B. Patil, Ed.
Internet-Draft
Intended status: Informational S. Probasco
Expires: August 27, 2011 G. Bajko
Nokia
B. Rosen
Neustar
February 23, 2011
Protocol to Access White Space database: Problem statement and
Requirements
draft-patil-paws-problem-stmt-01
Abstract
Governments around the world continue to search for new pieces of
radio spectrum which can be used by the expanding wireless
communications industry to provide more services in the usable
spectrum. The concept of allowing secondary transmissions (licensed
or unlicensed) in frequencies occupied by a primary user 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. This document discusses the requirements and the
problems that need to be addressed for enabling the use of white
space spectrum by obtaining information from such a database.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Prior Work . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. The concept of Cognitive Radio . . . . . . . . . . . . . . 7
3.2. Background information on white space in US . . . . . . . 8
3.3. Air Interfaces . . . . . . . . . . . . . . . . . . . . . . 8
4. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Global applicability . . . . . . . . . . . . . . . . . . . 9
4.2. Database discovery . . . . . . . . . . . . . . . . . . . . 10
4.3. Data model definition . . . . . . . . . . . . . . . . . . 11
4.4. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Informative References . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
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 took beginning steps when they published
their first ruling on use of TV white space, and then followed 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.
The concept of allowing secondary transmissions in frequencies
occupied by a primary user 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.
The fundamental issue is how to determine for a specific location and
specific time if of the spectrum are 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 it location. The database intersects the
exclusion zones with the querier 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
reports from ECC and Ofcom. In any country, the rules for which
primary entities are entitled to protection, how the exclusion zones
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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.
In a typical implementation of geolocation and database to access TV
white space, a radio is configured with its location in latitude and
longitude. There are multiple ways to configure this location
information, e.g. programmed at installation (e.g. for a fixed
device) or determined by GPS (e.g. for a or mobile device). At
power-on, before the device can transmit in TV white space
frequencies, the device must contact a database, provide its
geolocation and receive in return a list of unoccupied or "white
space" spectrum (for example, in a TV White space implementation, the
list of available channels at that location). The device can then
select one of the channels from the list (note that it is possible
they list is empty; there are no unoccupied channels at the location
of the device) and then begins to transmit and receive on the
selected channel. The device must query the database again for a
list of unoccupied channels based on certain conditions, e.g. a fixed
amount of time has passed, the device has changed location beyond a
specified threshold. The basic scenario is that before transmitting
in TV white space, the device must get permission from the database.
This arrangement assumes that the device querying can complete a
query before it transmits, or some other entity is able to query the
database. A common arrangement for this kind of service is a fixed
tower with a wired infrastructure that provides Internet service to a
network of client devices. In this scenario, the tower has Internet
access from its upstream service, and can query the database for
channels within the tower service area. It can then provide beacon
service to its clients, and assign them channels within the list of
channels that the tower gets from the database.
Another arrangement might be an ad-hoc mobile network where one or
more members of the ad hoc network have an independent radio IP
connection (perhaps a commercial cellular wireless data network)
which can be used to query the database over the Internet.
A third possibility is a mechanism where the database is accessed on
a private IP network.
The low frequencies of the TV bands have good propagation
characteristics. At these low frequencies, a radio signal will
travel ~3 times further than traditional WLAN at 2.5 GHz, assuming
the same transmit power. Because of these characteristics and new
cognitive radio techniques, when TV white space becomes available,
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this will enable new use cases and new business opportunities. Not
only is the capacity of new spectrum needed, but this propagation
trait by itself makes TV white space attractive for providing
broadband wireless access in rural, sparsely populated areas, as well
as for extended range home hot-spot coverage (similar to WLAN today,
but with improved coverage). In addition to propagation
characteristics, the geolocation database may provide new
capabilities for devices that use TV white space. When a device
using TV white space registers its location in the database, this
simple act makes the location of the device available for location
based services.
Other spectrum that might also be available for sharing using white
space techniques exist in every country. A great many primary users
were allocated space a time when there were many fewer potential
users of the space, and the primary users are not making efficient
(in geospatial and time aspects) use of the space. In the past,
relocating existing primary users was the only feasible alternative.
Using white space techniques to share spectrum without imposing
burdens on the primary users is more attractive.
This document discusses the requirements for accessing a database on
the Internet or a private IP network to obtain information that
enables a device to operate/use the available spectrum at a given
location. It also identifies various issues that need to be
addressed by the protocol between the device and database.
2. Terminology
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.
TV White Space
TV white space refers specifically to radio spectrum which has
been allocated for over the air television 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 Device
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
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space device is required to query a database with its location to
obtain information about available spectrum.
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.
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.
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.
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.
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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].
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.
4. Problem Statement
The use of white space spectrum is enabled via the capability of a
device to query a database and obtain information about the
availability of spectrum for use at a given location. The databases
are reachable via the Internet and the devices querying these
databases are expected to have some form of Internet connectivity,
directly or indirectly. The databases may be country specific since
the available spectrum and regulations may vary, but the fundamental
operation of the protocol should be country independent.
An example high-level architecture of the devices and white space
databases is shown in the figure below:
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-----------
|WS Device| ------------
|Lat: X |\ .---. /--------|Database X|
|Long: Y | \ ( ) / ------------
----------- \-------/ \/ o
( Internet ) o
----------- /------( )\ o
|WS Device| / (_____) \ ------------
|Lat: X |/ \--------|Database Y|
|Long: Y | ------------
-----------
Figure 1: High level view of the White space database architecture
In the figure above, note that there could be multiple databases
serving white space devices. The databases are country specific
since the regulations and available spectrum may vary. In some
countries, for example, the U.S., the regulator has determined that
multiple, competing databases may provide service to White Space
Devices.
A messaging interface between the white space devices and the
database is required for operating a network using the white space
spectrum. The following sections discuss various aspects of such an
interface and the need for a standard. Other aspects of a solution
including provisioning the database, and calculating protected
contours are considered out of scope of the initial effort, as there
are significant differences between countries and spectrum bands.
4.1. Global applicability
The use of TV white space spectrum is currently approved by the FCC
in the United States. However regulatory bodies in other countries
are also considering similar use of available spectrum. The
principles of cognitive radio usage for such spectrum is generally
the same. Some of the regulatory details may vary on a country
specific basis. However the need for devices that intend to use the
spectrum to communicate with a database remains a common feature.
The database provides a known, specifiable Protection Contour for the
primary user, not dependent on the characteristics of the White Space
Device or it's ability to sense the primary use. It also provides a
way to specify a schedule of use, because some primary users (for
example, wireless microphones) only operate in limited time slots.
Devices need to be able to query a database, directly or indirectly
over the public Internet and/or private IP networks prior to
operating in available spectrum. Information about available
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spectrum, schedule, power, etc. are provided by the database as a
response to the query from a device. The messaging interface needs
to be:
1. Radio/air interface agnostic - The radio/air interface technology
used by the white space device in available spectrum can be
802.11af, 802.16, 802.22, LTE etc. However the messaging
interface between the white space device and the database should
be agnostic to the air interface while being cognizant of the
characteristics of various air-interface technologies and the
need to include relevant attributes in the query to the database.
2. Spectrum agnostic - the spectrum used by primary and secondary
users varies by country. Some spectrum has an explicit notion of
a "channel" a defined swath of spectrum within a band that has
some assigned identifier. Other spectrum bands may be subject to
white space sharing, but only have actual frequency low/high
parameters to define protected entity use. The protocol should
be able to be used in any spectrum band where white space sharing
is permitted.
3. Globally applicable - A common messaging interface between white
space devices and databases will enable the use of such spectrum
for various purposes on a global basis. Devices can operate in
any country where such spectrum is available and a common
interface ensures uniformity in implementations and deployment.
Since the White Space device must know it's geospatial location
to do a query, it is possible to determine which database, and
which rules, are applicable, even though they are country
specific.
4. Address regulatory requirements - Each country will likely have
regulations that are unique to that country. The messaging
interface needs to be flexible to accommodate the specific needs
of a regulatory body in the country where the white space device
is operating and connecting to the relevant database.
4.2. Database discovery
Another aspect of the problem space is the need to discover the
database. A white space device needs to find the relevant database
to query based on its current location or for another location.
Since the spectrum and databases are country specific, the device
will need to discover the relevant database. The device needs to
obtain the IP address of the specific database to which it can send
queries in addition to registering itself for operation and using the
available spectrum.
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A database discovery mechanism needs to be specified. Reuse of
existing mechanisms is an option and could be adapted for meeting the
specific needs of cognitive radio technology.
4.3. Data model definition
The contents of the queries and response need to be specified. A
data model is required which enables the white space device to query
the database while including all the relevant information such as
geolocation, radio technology, power characteristics, etc which may
be country and spectrum dependent. All databases are able to
interpret the data model and respond to the queries using the same
data model that is understood by all devices.
Use of XML for specifying a data model is an attractive option. The
intent is to evaluate the best option that meets the need for use
between white space devices and databases.
4.4. Protocol
The protocol requirements are simple: registration and query
transactions are needed. In some circumstances, a registration
transaction is required prior to being able to query. The device
provides some identifying information, and the database responds with
an acknowledgement or error. The query protocol is a simple query/
response action (primarily location in, available spectrum out), with
some error conditions.
It may be possible to use existing protocols (e.g. LoST [RFC5222])
or it may be more appropriate to define a new protocol for this
purpose. HTTP transport is probably appropriate.
5. IANA Considerations
This document has no requests to IANA.
6. Security Considerations
The messaging interface between the white space device and the
database needs to be secured. Both the queries and the responses
need to be delivered securely. The device must be certain it is
talking to a bona fide database authoritative for the location and
spectrum band the device operates on. The database may need to
restrict interactions to devices that it has some prior relationship
with, or may be restricted from providing service to devices that are
not authorized in some manner.
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As the device will query with it's location, the location must be
protected against eavesdropping. Some regulations include personally
identifiable information as required elements of registration and/or
query and must similarly be protected.
All communications between the device and the database will require
integrity protection.
Man-in-the-middle attacks could modify the content of a response
which can cause problems for other networks or devices operating at a
given location. Interference as well as total loss of service could
result from malicious information being delivered to a white space
device.
This document describes the requirements and problems that need to be
addressed for a messaging interface between white space devices and
databases and does not by itself raise any security concerns.
7. Informative References
[DDR] Ofcom - Independent regulator and competition authority
for the UK communications industries, "Digital Dividend
Review; http://stakeholders.ofcom.org.uk/spectrum/
project-pages/ddr/".
[DTV] "Digital TV Transition; http://www.dtv.gov".
[ECC Report 159]
Electronic Communications Committee (ECC) within the
European Conference of Postal and Telecommunications
Administrations (CEPT), "TECHNICAL AND OPERATIONAL
REQUIREMENTS FOR THE POSSIBLE OPERATION OF COGNITIVE RADIO
SYSTEMS IN THE 'WHITE SPACES' OF THE FREQUENCY BAND 470-
590 MHZ; http://www.erodocdb.dk/Docs/doc98/official/pdf/
ECCREP159.PDF", January 2011.
[FCC ruling]
Federal Communications Commission, "Unlicensed Operation
in the TV Broadcast Bands;
http://edocket.access.gpo.gov/2010/pdf/2010-30184.pdf",
December 2010.
[RFC5222] Hardie, T., Newton, A., Schulzrinne, H., and H.
Tschofenig, "LoST: A Location-to-Service Translation
Protocol", RFC 5222, August 2008.
[Spectrum Framework Review]
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Ofcom - Independent regulator and competition authority
for the UK communications industries, "Spectrum Framework
Review;
http://stakeholders.ofcom.org.uk/consultations/sfr/",
February 2005.
Authors' Addresses
Basavaraj Patil (editor)
6021 Connection drive
Irving, TX 75039
USA
Email: basavaraj.patil@nokia.com
Scott Probasco
Nokia
6021 Connection drive
Irving, TX 75039
USA
Email: scott.probasco@nokia.com
Gabor Bajko
Nokia
323 Fairchild drive 6
Mountain view, CA 94043
USA
Email: gabor.bajko@nokia.com
Brian Rosen
Neustar
470 Conrad Dr
Mars, PA 16046
USA
Email: brian.rosen@neustar.biz
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