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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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