 Abstract—Cognitive radio is viewed as a novel approach for improving
the utilization of a precious natural resource: the radio
electromagnetic spectrum.
The cognitive radio, built on a software-defined radio, is defined
as an intelligent wireless communication system that is
aware of its environment and uses the methodology of understanding-
by-building to learn from the environment and adapt
to statistical variations in the input stimuli, with two primary
objectives in mind:
• highly reliable communication whenever and wherever
needed;
• efficient utilization of the radio spectrum.
Following the discussion of interference temperature as a new
metric for the quantification and management of interference, the
paper addresses three fundamental cognitive tasks.
1) Radio-scene analysis.
2) Channel-state estimation and predictive modeling.
3) Transmit-power control and dynamic spectrum management.
This paper also discusses the emergent behavior of cognitive radio.
Index Terms—Awareness, channel-state estimation and predictive
modeling, cognition, competition and cooperation, emergent
behavior, interference temperature, machine learning, radio-scene
analysis, rate feedback, spectrum analysis, spectrum holes, spectrum
management, stochastic games, transmit-power control,
water filling.
I. INTRODUCTION
A. Background
THE electromagnetic radio spectrum is a natural resource,
the use of which by transmitters and receivers is licensed
by governments. In November 2002, the Federal Communications
Commission (FCC) published a report prepared by the
Spectrum-Policy Task Force, aimed at improving the way in
which this precious resource is managed in the United States [1].
The task force was made up of a team of high-level, multidisciplinary
professional FCC staff—economists, engineers, and
attorneys—from across the commission’s bureaus and offices.
Among the task force major findings and recommendations, the
second finding on page 3 of the report is rather revealing in the
context of spectrum utilization:
Manuscript received February 1, 2004; revised June 4, 2004.
The author is with Adaptive Systems Laboratory, McMaster University,
Hamilton, ON L8S 4K1, Canada (e-mail: haykin@mcmaster.ca).
Digital Object Identifier 10.1109/JSAC.2004.839380
“In many bands, spectrum access is a more significant
problem than physical scarcity of spectrum, in large
part due to legacy command-and-control regulation that
limits the ability of potential spectrum users to obtain such
access.”
Indeed, if we were to scan portions of the radio spectrum including
the revenue-rich urban areas, wewould find that [2]–[4]:
1) some frequency bands in the spectrum are largely unoccupied
most of the time;
2) some other frequency bands are only partially occupied;
3) the remaining frequency bands are heavily used.
The underutilization of the electromagnetic spectrum leads us
to think in terms of spectrum holes, for which we offer the following
definition [2]:
A spectrum hole is a band of frequencies assigned to a primary
user, but, at a particular time and specific geographic location,
the band is not being utilized by that user.
Spectrum utilization can be improved significantly by making
it possible for a secondary user (who is not being serviced) to
access a spectrum hole unoccupied by the primary user at the
right location and the time in question. Cognitive radio [5], [6],
inclusive of software-defined radio, has been proposed as the
means to promote the efficient use of the spectrum by exploiting
the existence of spectrum holes.
But, first and foremost, what do we mean by cognitive radio?
Before responding to this question, it is in order that we address
the meaning of the related term “cognition.” According to the
Encyclopedia of Computer Science [7], we have a three-point
computational view of cognition.
1) Mental states and processes intervene between input
stimuli and output responses.
2) The mental states and processes are described by
algorithms.
3) The mental states and processes lend themselves to scientific
investigations.
Moreover, we may infer from Pfeifer and Scheier [8] that the
interdisciplinary study of cognition is concerned with exploring
general principles of intelligence through a synthetic methodology
termed learning by understanding. Putting these ideas together
and bearing in mind that cognitive radio is aimed at improved
utilization of the radio spectrum, we offer the following
definition for cognitive radio.
Cognitive radio is an intelligent wireless communication
system that is aware of its surrounding environment (i.e., outside
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