Cognitive radio is an intelligent wireless communication system that is aware of its environment and can learn and adapt to better utilize available spectrum. It aims for highly reliable communication and efficient spectrum usage. Cognitive radios use radio scene analysis to detect spectrum holes by analyzing signals over time and space. They also estimate interference temperature using spectral estimation and adaptive beamforming. Transmit power control and dynamic spectrum management allow cognitive radios to opportunistically access spectrum holes while avoiding interference. Future work may focus on language understanding, MIMO techniques, and nanoscale processing to improve cognitive radio capabilities.

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Cognitive Radio: BrainCognitive Radio: Brain--
Empowered WirelessEmpowered Wireless
CommunicationsCommunications
2006/10/16 Min Hong
Simon Haykin,
IEEE Journal on,
Vol.23, Iss.2, Feb. 2005

2. Introduction
Receiver
Transmitter
1
2
3
Radio scene analysis
Interference temperature
Channel state estimation and predictive modeling
Contents
Discussion and Conclusions4
Transmit power control
Dynamic spectrum management

3. Introduction
Definition of Cognitive Radio
Cognitive radio is an intelligent wireless communication
system that is aware of its surrounding environment and
uses the methodology to learn from the environment and
adapt its internal state
Primary objectives
Highly reliable communications whenever and wherever
Efficient utilization of the radio spectrum

4. Introduction
Spectrum holes
Spectrum holes
•A spectrum holes is
a band of frequencies
assigned to a primary user,
but at a particular time
and specific geographic
location,
the ban is not being
utilized that user

5. Introduction
Basic cognitive cycle

6. Introduction
Purpose of this Paper
How do cognitive radios learn best? (by Mitola, 2000)
The internal tuning of parameters
The external structuring of the environment to enhance
machine learning
Since many aspects of wireless networks are artificial,
they may be adjusted to enhance machine learning
Presenting detailed expositions of signal processing and
adaptive procedure

7. Radio-scene analysis
Signals depend on both time and space
Space-time processing
Adaptive beamforming for interference control
Estimation of he interference temperature
Detection of spectrum holes
Time-Frequency distribution
The incoming RF stimuli are sectioned into a continuous sequence of
successive busts
The section is long enough to produce an accurate spectral estimate

8. Radio-scene analysis
Multitaper Spectral Estimation
Accounting for the temporal characteristic of RF stimuli

9. Radio-scene analysis
Adaptive Beamforming for Interference Control
Accounting for the spatial characteristic of RF stimuli
There are two stages
Transmitter Receiver
• Power is preserved by avoiding
radiation of the transmitted signal
in all directions
• Interference at the receiver due
to the actions of other transmitters
is minimized
•It is performed for the adaptive
cancellation
• It protects the target RF signal
and place nulls along the
directions of interferers

10. Interference Temperature Estimation
The receiver be provided with a reliable spectral estimate
of the interference temperature
Cognitive radio is receiver-centric
Requirements
Time
Use the multitaper method to estimate the power spectrum of the
interference temperature
Space
Use a large number of sensors to properly sniff the RF environment

11. Interference Temperature Estimation
Interference Temperature model

12. Detection of spectrum holes
Three types of spectra
Black spaces
Occupied by high power local
interferers some of time
Candidate,
If it is switched OFF
Grey spaces
Partially occupied by low power
interferers
Free of RF interferes except for
ambient noise, made up of natural and
artificial forms of noise
Candidate
White spaces Candidate

13. Detection of spectrum holes
Practical issues
Environmental factors
Path loss
The diminution of received signal power with distance
Shadowing
The diminution of received signal power with obstacles
Exclusive zones
The area inside which the spectrum is free of use and can be made
available to an unserviced operator
The primary user happens to operate outside the exclusion zone
Ad-hoc networks are designed to operate at very low transmit powers
Predictive capability for future use

14. Channel state estimation & predictive modeling
Traditional ways
Differential detection
Use of M-ary phase modulation
Pilot transmission
Periodic transmission of a pilot
Semi-bind training
Supervised training mode
Performed under the supervision of a short training sequence
Tracking mode
The training sequence is switched off, actual data transmission is
initiated

15. Transmit power control
Conventional wireless communication
Centralized and receiver side
Cognitive radio
Decentralized manner and transmitter side
How can transmit-power control be achieved at the transmitter?
Cooperative mechanism & competitive mechanism
Base Station

16. Transmit power control
Cooperation vs. Competition
Competition mechanism
• Limitations imposed on
available network resources
• A user may try to exploit
the cognitive radio channel
for self-enrichment
• Interference temperature
limit imposed by regulatory
agencies
• A limited number of
spectrum holes
Cooperative mechanism
• Etiquette and protocol for
their individual safety and
benefit
• Cooperative ad hoc
networks
• Users of cognitive radio
may be able to benefit from
cooperation with each other
Multi-user Cognitive
Radio

17. Stochastic games
Nash Equilibrium (Prisoner's dilemma)
Limitations
• It assumes that all players
have same strategy and
interest
• It can not confine an
equilibrium condition

18. Stochastic games
Water filling
Definition of problem
Giver a limited number of spectrum holes, select the transmit
power levels of n unserviced users so as to jointly maximize their
data transmission rates, subject to the constraint that the
interference temperature limit is not violated
Competitive optimality
Considering a multi-user cognitive radio environment viewed as a
noncooperative game, maximize the performance of each
unserviced transceiver, regardless of what all the other transceivers
do, but subject to the constraint that the interference temperature
limit not be violated

19. Dynamic spectrum management
Purpose
To develop an adaptive strategy for the efficient and
effective utilization of RF spectrum
Spectrum management algorithm
Building on the spectrum holes detected by the radio-scene
analyzer and the output of transmit power controller, select
a modulation strategy that adapts to the time-varying
conditions of the radio environment, all the time assuring
reliable communication across the channel
Two considerations
Modulation and Traffic

20. Dynamic spectrum management
Modulation considerations
A modulation strategy is the OFDM in cognitive radio
Flexibility and computational efficiency

21. Dynamic spectrum management
Traffic considerations
There is a phenomenon called cell breathing in CDMA
Considering traffic and interference level
Traffic model
The means for predicting the future
traffic patterns
Makes it possible to predict the duration
for the spectrum hole which is vacated by the incumbent primary user
Two class of traffic data pattern in wireless environment
Deterministic patter : assigned a fixed time slot for transmission
Stochastic patterns : traffic data can only be described in statistical term

22. Discussion & Conclusions
Future works
Language understanding
For satisfying user’s need accurately
Cognitive MIMO radio
For a spectacular increase in the spectral efficiency and flexibility
of wireless communication
Cognitive turbo processing
Nanoscale processing
Conclusions
Trust by users of cognitive radio
Trust by all other user who might be interfered with

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Q&AQ&A