NIST Standards EducationDynamic Spectrum Access Systems

Martin BH Weiss

School of Information Sciences

University of Pittsburgh

mbw@pitt.edu

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• 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

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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

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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