Cognitive Radio: Brain- Empowered Wireless...
Transcript of Cognitive Radio: Brain- Empowered Wireless...
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Cognitive Radio: BrainCognitive Radio: Brain--Empowered Wireless Empowered Wireless
CommunicationsCommunications
2006/10/16 Min Hong
Simon Haykin,IEEE Journal on,
Vol.23, Iss.2, Feb. 2005
Introduction
Receiver
Transmitter
1
2
3
Radio scene analysisInterference temperatureChannel state estimation and predictive modeling
Contents
Discussion and Conclusions 4
Transmit power controlDynamic spectrum management
Introduction
Definition of Cognitive RadioCognitive 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 objectivesHighly reliable communications whenever and wherever
Efficient utilization of the radio spectrum
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 beingutilized that user
Introduction
Basic cognitive cycle
Introduction
Purpose of this PaperHow 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
Radio-scene analysis
Signals depend on both time and space
Space-time processingAdaptive 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
Radio-scene analysis
Multitaper Spectral EstimationAccounting for the temporal characteristic of RF stimuli
Radio-scene analysis
Adaptive Beamforming for Interference ControlAccounting 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
Interference Temperature Estimation
The receiver be provided with a reliable spectral estimate of the interference temperature
Cognitive radio is receiver-centric
RequirementsTime
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
Interference Temperature Estimation
Interference Temperature model
Detection of spectrum holes
Three types of spectra
Black spacesOccupied by high power local interferers some of time
Candidate, If it is switched OFF
Grey spacesPartially 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
Detection of spectrum holes
Practical issuesEnvironmental 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
Channel state estimation & predictive modeling
Traditional waysDifferential 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
Transmit power control
Conventional wireless communicationCentralized 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
Transmit power control
Cooperation vs. Competition
Competition mechanism• Limitations imposed onavailable network resources• A user may try to exploitthe cognitive radio channelfor self-enrichment• Interference temperature limit imposed by regulatoryagencies • 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 CognitiveRadio
Stochastic games
Nash Equilibrium (Prisoner's dilemma)
Limitations
• It assumes that all players have same strategy and interest • It can not confine anequilibrium condition
Stochastic games
Water fillingDefinition 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
Dynamic spectrum management
Purpose To develop an adaptive strategy for the efficient and effective utilization of RF spectrum
Spectrum management algorithmBuilding 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 considerationsModulation and Traffic
Dynamic spectrum management
Modulation considerationsA modulation strategy is the OFDM in cognitive radio
Flexibility and computational efficiency
Dynamic spectrum management
Traffic considerationsThere is a phenomenon called cell breathing in CDMA
Considering traffic and interference level
Traffic modelThe 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 environmentDeterministic patter : assigned a fixed time slot for transmission
Stochastic patterns : traffic data can only be described in statistical term
Discussion & Conclusions
Future worksLanguage 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
ConclusionsTrust by users of cognitive radio
Trust by all other user who might be interfered with
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