A Survey on Spectrum Management in Cognitive Radio

8/17/2019 A Survey on Spectrum Management in Cognitive Radio

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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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Spectrum Hole


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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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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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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

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• 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 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 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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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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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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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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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 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

Documents

A Survey on Spectrum Management in Cognitive Radio