A discussion on channel sensing techniques By James Xu Supervised by Dr. Fakhrul Alam.
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Transcript of A discussion on channel sensing techniques By James Xu Supervised by Dr. Fakhrul Alam.
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Channel Sensingfor Cognitive Radio
A discussion on channel sensing techniques
By James XuSupervised by Dr. Fakhrul Alam
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Presentation overview
Introduction to wireless communications What is Cognitive Radio (CR)? Why do we need CR? What is channel sensing Our workbench setup Our research Our major contributions Conclusion
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Wireless communications
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What is Cognitive Radio (CR) Able to sense spectral environment Able to provide opportunistic access
Find gaps in the spectrumAdjust system parameters to utilize it
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Why do we need CR?
Unlicensed spectrum is rare Almost none available under 3GHz
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Why do we need CR? Licensed to primary user only (Incumbent) We are running out of space, and higher frequency
has problems We are under utilizing licensed space
CR is allowed usage (guarantee interference free)
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What is channel sensing
The first step of CR is to identify free spectrum
Channel sensing is one of the most fundamental part of CR
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What is channel sensing
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Our research
Our research focus Energy detection Cyclostationary feature extraction
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Our CR workbench
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Energy detection
Easy to implement Fast Not effective under low SNR
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What is energy detection? All radio transmission have energy
Based on hypothesis testing
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Energy detector
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Energy detector
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Problems with the detector Misdetection on Narrowband signals
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Problems with the detector Misdetection on partial signals
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Adaptive energy detection We proposed an
improvement Introduced adaptive
detection
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Improved detection
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Adaptive ED characteristics
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Adaptive ED characteristics
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Cyclostationary Features
Another channel sensing strategy Digital communication systems have
built in periodicity A signal is a first order cyclostationary if
it’s mean is periodic A signal is second order cyclostationary
it it’s auto-correlation is periodic
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Cyclostationary Features
Auto-correlation how much a signal has in common with itself, against delay
Alpha = Cyclic frequency S = Spectrum Correlation Function (SCF)
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Cyclostationary Features
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Work in Progress
This is preliminary, a proof of concept Could be done in future research
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Our major contributions
Xu J. Y., Alam, F., Adaptive Energy Detection for Cognitive Radio: An Experimental Study, ICCIT, 2009
IET PATW Competition, Regional winner cr.jamesyxu.com Svn://cr.jamesyxu.com/svn CRLibs
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CRLibs
A library for cognitive radio research
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Conclusion
Workbench setup Investigated various channel sensing
techniques (ED, SCF, Spectral Entropy) Proposed and implemented
improvements (AED) Consolidated library (CRLibs), examples
and codebase (SVN) Full progress documentation (SVN, CR)
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Acknowledgement
Dr Fakhrul Alam Dr James Chang Dr Tom Moir Everyone in our lab
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Thank you for listening
You are invited to visit our CR workbench at Building 80
Much more details in the project report Adaptive energy detection model will be
on IEEEXplore end of December Any questions?