认知无线电的一种应用协议IEEE802.22协议
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IEEE 802.22: The First Worldwide Wireless Standard based on Cognitive Radios
Carlos Cordeiro, Kiran Challapali, Dagnachew Birru, and Sai Shankar N
*
Philips Research USA
Briarcliff Manor, NY 10510
{Carlos.Cordeiro, Kiran.Challapali, Dagnachew.Birru, Sai.Shankar}@philips.com
Abstract – In November/2004, we witnessed the
formation of the first worldwide effort to define a
novel wireless air interface
1
standard based on
Cognitive Radios (CRs): the IEEE 802.22 Working
Group (WG). The IEEE 802.22 WG is chartered with
the development of a CR-based Wireless Regional
Area Network (WRAN) Physical (PHY) and Medium
Access Control (MAC) layers for use by license-
exempt devices in the spectrum that is currently
allocated to the Television (TV) service. Since 802.22
is required to reuse the fallow TV spectrum without
causing any harmful interference to incumbents (i.e.,
the TV receivers), cognitive radio techniques are of
primary importance in order to sense and measure
the spectrum and detect the presence/absence of
incumbent signals. On top of that, other advanced
techniques that facilitate coexistence such as dynamic
spectrum management and radio environment
characterization could be designed. In this paper, we
provide a detailed overview of the 802.22
architecture, its requirements, applications, and
coexistence considerations that not only form the
basis for the definition of this groundbreaking
wireless air interface standard, but that will also serve
as foundation for future research in the promising
area of CRs.
I.
INTRODUCTION
The proliferation of wireless services and devices for
uses such as mobile communications, public safety, Wi-
Fi, and TV broadcast serve as the most indisputable
example of how much the modern society has become
dependent on radio spectrum. While land and energy
constituted the most precious wealth creation resource
during the agricultural and industrial eras respectively,
radio spectrum has become the most valuable resource of
the modern era [1]. Notably, the unlicensed bands (e.g.,
ISM and UNII) play a key role in this wireless ecosystem
1
In this work, the term air interface is used to refer to the PHY
and MAC layers of the ISO/OSI protocol reference model.
* Sai Shankar is currently with Qualcomm Inc. His email
address is nsai@qualcomm.com.
given that many of the significant revolutions in radio
spectrum usage has originated in these bands, and which
resulted in a plethora of new applications including last-
mile broadband wireless access, health care, wireless
PANs/LANs/MANs, and cordless phones. This explosive
success of unlicensed operations and the many
advancements in technology that resulted from it, led
regulatory bodies (e.g., the FCC through its Spectrum
Policy Task Force (SPTF) [2]) to analyze the way
spectrum is currently used and, if appropriate, make
recommendations on how to improve radio resource
usage.
As indicated by the SPTF and also by numerous reports
[3], the usage of radio resource spectrum experiences
significant fluctuations. For example, based on the
measurements carried out in [4] for the frequency bands
below 3GHz and conducted from January/2004 to
August/2005, we conclude that, on an average, only
about 5.2% of the spectrum is actually in use in the US in
any given location and at any given time (please refer to
[4] for more detailed information). Interestingly enough,
these measurements reveal that heavy spectrum
utilization often takes place in unlicensed bands while
licensed bands often experience low (e.g., TV bands) or
medium (e.g., some cellular bands) utilization. These
striking results coupled with recent advancements in
radio technology led the FCC to revisit the traditional
way of spectrum management. It has been realized that
not only spectrum usage is very low in certain licensed
bands, but also that the scarcity of radio resources is
becoming a crisis hindering the development of many
wireless applications including broadband access (not
only in urban/suburban areas, but especially in
rural/remote areas), public safety, health care, business,
and leisure.
Cognitive Radios (CRs) [5][6][7] are seen as the solution
to the current low usage of the radio spectrum. It is the
key technology that will enable flexible, efficient and
reliable spectrum use by adapting the radio’s operating
characteristics to the real-time conditions of the
environment. CRs have the potential to utilize the large
amount of unused spectrum in an intelligent way while
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