Download Presentation - M. Javad Omidi

Spectrum Sensing
Marjan Hadian
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Outline
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Cognitive Cycle
Enrgy Detection
Matched filter
cyclostationary feature detector
Interference Temperature
Spectral Estimation
Hidden node problem
Cooperative detection
detection methods
– log-likelihood combining
– weighted gain combining
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Cognitive Cycle
Mitola calls cognitive radio cycle: cognitive radio continually
observes the environment, orients itself, creates plans,
decides, and then acts
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Spectrum Sensing:
A cognitive radio monitors the available spectral
bands,captures their information, and detects the
spectrum holes.
• frequencies usage.
• mode identification.
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• Enrgy Detection
Where T calculated from:
most important problem of this, is which one called SNR wall.
This problem comes from uncertainty.
SNR wall is a minimum SNR below which signal cannot be
detected and formulas no longer holds
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• Matched filter
it maximizes SNR. For implementation of matched
filter cognitive radio has a priori knowledge of
modulation type, pulse shaping.
• cyclostationary feature detector
The main advantage of the spectral correlation
function is that it differentiates the noise energy
from modulated signal energy.
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Interference Temperature
As additional interfering signals appear the noise floor increases
and then unlicensed devices could use that particular band as
long as their energy is under mention noise floor
where
Joules per Kelvin
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Spectral Estimation
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parametric spectral estimation
Non-parametric spectral estimation
 Periodogram Spectral Estimator (PSE)
 Blackman-Tukey Spectral Estimator (BTSE)
 Minimum Variance Spectral Estimator (MVSE)
 Multi taper Method (MTM)
 Filter Bank Spectral Estimator (FBSE)
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Hidden node problem
Traditional detection problem: (a) Receiver uncertainty and (b) shadowing
uncertainty[5]
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Cooperative detection
• prevent the hidden terminal problem also
mitigate the multipath fading and shadowing
effect
• Information from multiple SUs are
incorporated for primary user detection.
• Implementation
 Centralized manner
 distributed manner
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How SU provide its observation to other nodes?!
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This transmission can overlap to the air interfaces already
present in the environment, so it can change the nature of
observations and make new problems. In order to solve this
problem several solutions suggested :
 two distinct networks are deployed separately
the sensor network for cooperative spectrum sensing and the
operational network for data transmission. This method
implemented in central manner[5]
 Sharing the analysis model in an off-line method when in the
environment no SUs is observing the radio scene[1]
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Without consideration of exchanging method, we assume that
the observation of SU i is due to its position and to the
state of radio source, but not to the observation of other
SU j and .Thus we assume that, independent measurements
for each SUs is presented either in a centralized or
distributed manner. Now we review two detection methods:
• log-likelihood combining
• weighted gain combining
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• log-likelihood combining
Assume that
is the vector of SUs energy detector output,
then we can write likelihood ratio test(LRT) as:
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weighted gain combining:
where
and
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Thanks for your attention.
Questions?
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