Transcript Energy detection for Cognitive Radio

By James Xu
Supervised by Dr. Fakhrul Alam
A discussion on channel sensing techniques
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

Wireless communications
What is Cognitive Radio (CR)
Able to sense spectral environment
 Able to provide opportunistic access

 Find gaps in the spectrum
 Adjust system parameters to utilize it
Why do we need CR?
Unlicensed spectrum is rare
 Almost none available under 3GHz

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)
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

What is channel sensing
Our research
Our research focus
 Energy detection
 Cyclostationary feature extraction

Our CR workbench
Energy detection
Easy to implement
 Fast
 Not effective under low SNR

What is energy detection?

All radio transmission have energy

Based on hypothesis testing
Energy detector
Energy detector
Problems with the detector

Misdetection on Narrowband signals
Problems with the detector

Misdetection on partial signals
Adaptive energy detection
We proposed an
improvement
 Introduced adaptive
detection


Improved detection
Adaptive ED characteristics
Adaptive ED characteristics
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

Cyclostationary Features

Auto-correlation how much a signal has in
common with itself, against delay
Alpha = Cyclic frequency
 S = Spectrum Correlation Function (SCF)

Cyclostationary Features
Work in Progress
This is preliminary, a proof of concept
 Could be done in future research

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

CRLibs

A library for cognitive radio research
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)

Acknowledgement
Dr Fakhrul Alam
 Dr James Chang
 Dr Tom Moir
 Everyone in our lab

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?
