NIST Standards Education
Dynamic Spectrum Access
Systems
Martin BH Weiss
School of Information Sciences
University of Pittsburgh
[email protected]
Overview
• What is dynamic spectrum access?
• Why should we care?
• What are some systems approaches to implementing
DSA?
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Learning Objectives
• After completing this module, you should be able to
• Describe the functions of DSA systems
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A Brief History
• In the beginning, signal processing and transmission
functions were performed in hardware
• It came to pass that signal processing could be
performed in software (software defined radio, or SDR)
• In 1999, Stephen Mitola proposed a cognitive radio that
could dynamically adapt to its (radio) environment
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Why Spectrum Sharing?
• Measurements suggest that many spectrum bands are
unutilized much of the time
• With the growth of wireless applications, an interest on
the part of sharing idle spectrum emerged among
spectrum entrants
• Generally, spectrum sharing is referred to as Dynamic
Spectrum Assignment (or DSA)
• In 2002, the FCC’s Spectrum Policy Task Force
recommended the adoption of spectrum sharing
technologies
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How DSA might work
• Spectrum entrants are considered secondary users
whose usage rights are inferior to the license holders’
• Secondary users must therefore minimize interference to
the primary user(s)
• This means that they must determine
•
•
•
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When primary users are not using the band
What frequency range is available
How to share with other secondary users
When primary users begin using the band again
• Transmission opportunities are referred to as spectrum
holes and can vary in space, time and frequency
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How DSA might work
From Akyildiz et.al. NeXt generation/dynamic spectrum access/cognitive radio wireless networks: A survey”
Computer Networks, V. 50 No. 13, pp 2127-2159, 2006
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Challenges with DSA
• Radio communication is fraught with uncertainties
• Signal fading due to multi-path propagation
• Shadowing due to manmade and natural objects
• Interference
• Natural and manmade noise
• Other radio signals (adjacent band, intermodulation
products, etc.)
• Thus, identifying a spectrum hole is difficult
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Approaches to DSA
implementation
• Spectrum sensing
• Databases
• Cooperative sharing
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Where are we today with DSA?
• TV White Spaces
• Approved by the FCC
• Spectrum holes are fairly static
• Database-oriented DSA
• Federal-commercial sharing
• Several bands are moving toward sharing
• Cooperative as well as database-oriented sharing
• Mostly still at the pilot project stage
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Summary
• Dynamic Spectrum Access (DSA) is emerging as an
approach to address spectrum shortages
• DSA requires the use of some context acquisition
approach, such as sensors, databases, or cooperation
• The technologies and business models associated with
DSA are still emerging
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