cogntive radio
TRANSCRIPT
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Presented by
Vibhor Aggarwal
Vibhuti Narain Singh
Cognitive Radio
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Outline
Today's wireless systems
Cognitive radio (CR) system Different types of cognitive radio
Characteristics of cognitive radio system
Spectrum hole concept
Levels of cognitive radio functionality
Cognitive radio operation
How is it different from simple radios
Applications of cognitive radio
Problems
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Todays Wireless System
Most of the spectrums (licensed bands) are already allocated
users for exclusive use.Few, Small, unlicensed bands are left open for unlicensed userbands 900MHz and 2.4 GHz)
Technological advancement has resulted in the huge developmpersonal wireless technologies like Wi-Fi/802.11, Bluetooth, dcordless phones, 3G, and so on which operate on unlicensed b
Licensed bands are under-utilized but unlicensed bands are crresulting on spectrum scarcity.
Solution is to let unlicensed users use the licensed frequenciesprovided they can guarantee interference perceived by the primlicense holders will be minimal (a concept of cognitive radio).
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Cognitive Radio(CR) Syste
Allows the unlicensed users to dynamically and opportunistica
the under-utilized" licensed bands
Cognitive Radio- Termed by Joseph Mitola in 1991:
- Radio that includes a transmitter in which operating para
such as frequency range, modulation type or maximum outpu
can be altered by software.
A software-defined radio with some artificial intelligence to ma
detection and wise decision according to its environment.
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Fig 1: An example of cognitive radio system components
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ContinueIn order to access under-utilized licensed bandsdynamically and opportunistically, Cognitive Radio h
to- identify the spectrum opportunities (idle frequen
bands) in spatial and frequency domain.
- or use the licensed spectrum with transmit
power constraint so that the interferencecreated by secondary users is below the
tolerable limit.
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Different types of Cognitive Radio
Full Cognitive Radio: every possible radio parameter is tak
account to make spectrum decision
Spectrum Sensing Cognitive Radio: only radio frequency (
spectrum is observed and used in decision making
Licensed Band Cognitive Radio: device is capable of using
spectrum in addition to unassigned spectrum
Unassigned Band Cognitive Radio: device is only allowed t
unassigned and/or license exempt spectrum
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Characteristics of Cognitive Ra
System
Cognitive capability
Ability to capture or sense the information from itsradio environment and allows to identify and select tportion of the spectrum that are unused at a specifictime or location.
Reconfiguration ability
Dynamically programmable capability according toradio environment to transmit and receive on a varieof frequencies.
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Spectrum management
Functions incorporated for adapting to the dynamic spectrenvironment:
Spectrum sensing
Spectrum decision
Spectrum sharing
Spectrum mobility
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Spectrum sensing
A function in CR networks to monitor the unused spectrum bands
Provides the spectrum availability information required for other It is achieved thorough:
PU detection
CR user observes and analyzes its local radio environmdetermines the presence of PU transmissions and accordinglythe current spectrum availability if exists.
Cooperation
Observed information by CR user is exchanged with itsneighbors to improve sensing accuracy
Sensing control
Coordinates the sensing operations of the CR users an
neighbors
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Spectrum Decision
A function to select the most appropriate band (after spectrum sens
according to the quality of service (QoS) requirement.
Spectrum selection decision is performed considering end-to-end
consisting of multiple hops.
Available spectrum bands in CR network may differ from one hop
It is achieved through:
Spectrum characterization
CR user observes the characteristics of each available
which may be varying over time and space due to PU
Spectrum Selection
CR user finds the best spectrum for each hope to sati
requirement for end-to-end route
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Spectrum Sharing
Enables CR users to perform channel selection and power
according to their QoS
It is achieved through:
Resource allocation
Based on QoS, CR users selects the proper channe
their transmission power.
Spectrum access
Enables multiple CR users to share the channel de
who will access the channel or when a user may a
channel.
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continue spectrum sharing
Medium access protocols for spectrum access
Random access
Channel may be opportunistically captured by any CR user fo
data exchanges
Time slotted
Control and data are assigned fixed durations and prevent sim
transmission by multiple users
Hybrid
Fixed time duration for control packets followed by random a
capturing the channel before data transfer.
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CR users are mobile and so called visitors to the spectrum
If the spectrum in use by a CR user is required for PU, the commu
the CR user needs to be continued in another vacant portion of t
Spectrum mobility is required when:
PU is detected
CR user loses its connection due to mobility of other users
Current spectrum band cannot provide the QoS requirement
Spectrum mobility
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continue spectrum mobility
Spectrum mobility is achieved through
Spectrum handoff
CR user switches the spectrum band physically and re
the communication parameters (e.g. operating frequen
modulation type)
Connection management
CR user sustains the QoS or minimizes quality degrada
spectrum switching by interacting with each layer.
l
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Spectrum Hole
Spectrum hole:Temporarily unused licensed
spectrum
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Levels of Cognitive Radio Function
Level Capability Comments
0 Pre-programmed A software radio
1 Goal Driven Chooses Waveform According to Goal. Requires
Environment Awareness.
2 Context Awareness Knowledge of What the User is Trying to Do
3 Radio Aware Knowledge of Radio and Network Components,
Environment Models
4 Capable of Planning Analyze Situation (Level 2& 3) to Determine Goapower), Follows Prescribed Plans
5 Conducts Negotiations Settle on a Plan with Another Radio
6 Learns Environment Autonomously Determines Structure of Environm
7 Adapts Plans Generates New Goals
8 Adapts Protocols Proposes and Negotiates New Protocols
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NormalUrgent
Allocate Resources
Initiate Processes
Parse Stimuli
Pre-process
Establish Priority
Normal
Negotiate
Immediate
LearnNew
StatesObserve
Outside
World
Act
User Driven(Buttons)
Autonomous
PlaStates
G
W
Cognitive
radio
operation
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What is SDR?A software-defined radio (SDR) system is a radio communication sy
can tune to any frequency band and receive any modulation across
frequency spectrum by means of a programmable hardware which
by software.
The ideal scheme would be to attach an analog to digital converte
antenna. A digital signal processor would read the converter, and th
would transform the stream of data from the converter to any othe
Relationship Between SDR and
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Relation
Cognitive radio is a revolut
evolution of software radio
Cognitive radio without SD
limited.
Spectrum
Deregula
-tion
Software
-defined
Radio
Cognitive
Radio
Drives
H i C iti R di Diff t f
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Cognitive Can create n
waveforms o
Can negotiatinterfaces
Adjusts oper
meet the Qorequired by application fsignal enviro
How is Cognitive Radio Different f
Other Radios? - ApplicationConventional
Radio
Supports a fixednumber of systems
Reconfigurabilitydecided at the
time of design May support
multiple services,but chosen at thetime of design
d ff f
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How is Cognitive Radio Different from O
Radios? -Design
Conventional
Radio
Traditional RF
Design
Traditional
Baseband Design
Cognitive R
SDR +
Intelligence
Awareness
Learning
Observations
H i C i i R di Diff f O
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How is Cognitive Radio Different from O
Radios?upgrade cycle
Conventional Radio Cannot be made
future proof
Typically radios are
not upgradeable
Cognitive
SDR upgradmechanism
upgrades
Collaboratiupgrades
Typical Cognitive Radio Applicati
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Typical Cognitive Radio Applicati
What doescognitive
radio
enable?
Bandwidth isnt scarce
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Measurements averagedover six locations:
1. Riverbend Park, Great Falls,VA,
2. Tysons Corner, VA,
3. NSF Roof, Arlington, VA,
4. New York City, NY
5. NRAO, Greenbank, WV,
6. SSC Roof, Vienna, VA
~25% occupancy at peak
Bandwidth isn t scarce,
its underutilized
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RF components are expensive
Cheaper analog implies more
spurs and out-of-band emissions
Processing is cheap and getting cheaper
Cognitive radios will adapt around spurs(just another interference source) orteach the radio to reduce the spurs
Better radios results in still more availablespectrum as the need arises.
Likely able to exploit SDR
Cognitive radio permits the deployment of ch
radios
Impro ed Link Reliabilit
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Improved Link Reliability
Cognitive radio is aware of areas with abad signal
Can learn the location of the bad signal Has insight
Radio takes action to compensate for lossof signal
Actions available:
Power, bandwidth, coding,
channel, form an ad-hoc network Radio learns best course of action
from situation
GoodSignal Quality Can aid cellular system Inform system & other radios of identified gaps
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Cognitive Radio and Military Networ
How is the military planning
on using cognitive radio?
Drivers in Commercial and Military Netw
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Drivers in Commercial and Military Netw Many of the same commercial applications also apply to military
networks
Opportunistic spectrum utilization
Improved link reliability
Cheaper radios Collaborative networks
Military has much greater need for advanced networking techniques
MANETs and infrastructure-less networks
Disruption tolerant
Dynamic distribution of services
Energy constrained devices
Goal is to intelligently adapt device, link, and network parameters to helpachieve mission objectives
Potential Problems with Networked Cog
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Potential Problems with Networked Cog
RadiosDistributed
Infinite recursions Instability (chaos)
Adaptation collisions
Equitable distribution of
resources
Byzantine failure
Information distribution
Centralized
Signaling Overhead
Complexity
Responsiveness
The future is
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The future is
Cognitive Radio
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QUESTIONS ARE WELCOM