a survey on spectrum management in cognitive radio
TRANSCRIPT
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A survey on Spectrum Managementin Cognitive Radio Networks
Ian F. Akyildiz, Won-Yeol Lee, Mehmet C. Vuran, Shantidev
MohantyGeorgia Institute of Technology
Communications Magazine, vol 46, April 2008, pp. 40-48
HY 539
Nov. 2009
S. Loutou
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Introduction
• Current Wireless Networks: Static spectrum
Allocation Policy & Spectrum Underutilization
• Cognitive Radio Technology: Share the
wireless channel with licensed users in an
opportunistic manner
• Provide high bandwidth to mobile users via
heterogeneous wireless architectures &
dynamic spectrum access techniques
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Emerging Issues –
Spectrum Management
• Determine which portions of the spectrum are
available: Spectrum Sensing
• Select the best available channel: Spectrum
Decision
• Coordinate access to this channel with other
users: Spectrum Sharing
• Vacate the channel when a licensed user is
detected: Spectrum Mobility
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Cognitive Radio Technology 1/3
• Definition: A radio that can change itstransmitter parameters based on interactionwith its environment
• Main Characteristics: Cognitive Capability : Identify the unused spectrum
at a specific time or location (Spectrum Holes/White Spaces)
Reconfigurability : Transmit and Receive on avariety of frequencies. Use different accesstechnologies
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Cognitive Radio Technology 2/3
Spectrum Hole
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Cognitive Radio Technology 3/3
Architecture• CR requires a novel radio
frequency (RF) transceiverarchitecture
• Main components:Radio front-end,Baseband processing unit
• Novel characteristic: RF front-end capable of simultaneous sensing over a
wide frequency range
RF hardware capable of being tuned to any part of alarge range of spectrum
RF front-end capable to detect a weak signal in a largedynamic range
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CR Network Architecture 1/3
Network Components
• Primary Network
• CR Network
• Primary Network
can have infrastructure
(Base Stations)
• CR network also
can have Base Stations
and Spectrum Brokers
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CR Network Architecture 2/3
Spectrum Heterogeneity
• CR networks : Licensed band operation
Unlicensed band operation
• Licensed band
CR focuses on the detection of PUs
CR should vacate if PU appears
The channel capacity depends on the interference
at nearby PUs• Unlicensed band
CR have the same access rights
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CR Network Architecture 3/3
Network Heterogeneity
• CR network access: Access their own CR basestation on both licensed and unlicensedspectrum bands – define their sharing policy
• CR ad hoc access: CR users communicatethrough ad hoc connection on both licensedand unlicensed spectrum bands
•
Primary Network access: CR users access theprimary base station through the licensedband – require adaptive MAC protocol
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Spectrum Management Framework
1/15
• Challenges: Coexistence with primary
networks & Diverse QoS requirements
• Design challenges:
Interference Avoidance
QoS Awareness, considering the dynamic and
heterogeneous spectrum environment
Seamless Communication regardless of the
appearance of PU
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Spectrum Management Framework 2/15
Spectrum Sensing
• Enables CR users to adapt to the environmentby detecting spectrum holes without causinginterference to the primary network
• Through a real-time wideband sensingcapability
• Spectrum sensing techniques:
–
Primary Transmitter Detection – Primary Receiver Detection
– Interference Temperature Management
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Spectrum Management Framework 3/15 Spectrum Sensing
Primary Transmitter Detection
Based on the detection of a weak signal fromPrimary Transmitter. 3 schemes used:
• Matched Filter Detection: When primaryinformation is known to CR
• Energy Detection: When primary info is notavailable. Susceptible in noise power
• Feature Detection: Detect the built-in periodicityor cyclostationarity that characterize modulatedsignals. Computational complex.
Sensing info from others users required:Cooperative Detection
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Spectrum Management Framework 4/ 15 Spectrum Sensing
Primary Receiver Detection &
Interference Temperature Management
• Most efficient way to detect holes: Detect the
PU that are receiving data within the
communication range of a CR• Interference Temperature: A limit to the
amount of new interference the receiver could
tolerate
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Spectrum Management Framework 5/15 Spectrum Sensing
Challenges
• Interference Temperature Measurement: CRuser cannot be aware of the precise locationof the PU
• Spectrum-Sensing in multi-user networks:More difficult to sense holes and estimateinterference
•
Spectrum-efficient sensing: Sensing cannot beperformed while transmitting – Minimizesensing time
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Spectrum Management Framework 6/15
Spectrum Decision
Define parameters to represent a particularspectrum band
• Interference: To estimate the permissible power
of a CR. Estimate channel capacity• Path Loss: Closely related to distance & frequency
• Wireless link errors: Depending on themodulation scheme and the interference level
• Link layer delay: different types required atdifferent bands
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Spectrum Management Framework 7/15 Spectrum Decision
Decision Procedure
• Considering QoS requirements & Spectrum
characteristics -> Configure transmission mode &
bandwidth
• Primary User Activity: New metric to describe thedynamic nature of CR
• Use of multiple noncontiguous spectrum bands
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Spectrum Management Framework 8/15 Spectrum Decision
Challenges
• Decision Model: Taking into account QoS
requirements at spectrum capacity estimation
• Cooperation with reconfiguration:
Transmissions parameters to be reconfigured
for optimal operation in certain bands
• Spectrum decision over heterogeneous
spectrum bands: On both licensed and
unlicensed bands
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Spectrum Management Framework 9/15
Spectrum Sharing
• Includes much of the functionality of a MAC
protocol
• Classified by 4 aspects
-Architecture
-Spectrum Allocation Behavior
-Spectrum Access Technique
-Scope
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Spectrum Management Framework 10/15 Spectrum Sharing
Architecture
• Centralized spectrum sharing:
– Controlled by a central unit.
– Distributed Sensing Procedure
• Distributed spectrum sharing : Local policies
performed by each node distributively
Distributed solutions follow the centralized,
but at the cost of message exchange
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Spectrum Management Framework 11/15 Spectrum Sharing
Allocation Behavior
• Cooperative spectrum sharing: The effect of thecommunication of one node on other nodes isconsidered. Share interference info locally
•
Non-cooperative spectrum sharing: Only a singlenode is considered. May result in reducedspectrum utilization
Cooperative approaches outperform and result to
a certain degree of fairnessNon-cooperative perform better at energyconsumption
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Spectrum Management Framework 12/15 Spectrum Sharing
Access Technology
• Overlay spectrum sharing: SUs use a portion
of the spectrum not used by Pus
• Underlay spectrum sharing: The transmission
of a CR is regarded as noise by PUs
Underlay techniques utilize higher bandwidth
but increase slightly the complexity
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Spectrum Management Framework 13/15 Spectrum Sharing
Scope
• Intranetwork: Spectrum
allocation between the
entities of a CR
network, withoutinterfere to PUs
• Internetwork: Enable
multiple systems to be
deployed in overlapping
locations and spectrum
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Spectrum Management Framework 14/15 Spectrum Sharing
Challenges
• Common Control Channel: Infeasible implementation-> Mitigation techniques or local CCC for clusters ornodes
• Dynamic Radio Range: Due to the interdependencybetween range and operating frequency, the neighborschange when the frequency change
• Spectrum Unit: Definition of a channel as spectrumunit
• Location Information: Assumption that the locationand transmit power of PUs are known is not alwaysvalid
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Spectrum Management Framework 15/15
Spectrum Mobility
• The necessity to change its operating
spectrum bands: Spectrum Handoff
• Ensure smooth and fast transition leading to
min performance degradation
• Challenges: Spectrum mobility in
– Time domain
– Space
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CONCLUSION
• CR networks will provide a spectrum-aware
communication
• Solve wireless network problems resulting
from the limited available spectrum
• More research required along the lines
introduced in this survey