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Cognitive Radio Networks
Zhu JiemingGroup Presentaion
Aug. 29, 2011
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Outline
1. Wireless mobile communication2. Introduction to cognitive radio networks3. Dynamic spectrum management4. Interference mitigation 5. Summary
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1. Wireless mobile communication
The development of wireless mobile communications
Directions for development
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1. Wireless mobile communication
1G:Analog mobile phone
FDMA (Frequency Division Multiple Access)
Low system capacity
and security problems
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1. Wireless mobile communication
2G:GSM (Global System for Mobile Communications)
TDMA (Time Division Multiple Access)
SMS (Short Message Service)
Data Rate: 9.6kbps
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1. Wireless mobile communication
2.5G/2.75G:Circuit switch Packet switch
2.5G: GPRS (General Packet Radio Service)
2.75G: EDGE (Enhanced Data Rate for GSM
Evolution)
Data Rate: 384kbps
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1. Wireless mobile communication
3G:CDMA (Code Division Multiple Access)
Data Rate: 2.4Mbps
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1. Wireless mobile communication
4G(Standardization is on-going):OFDMA (Orthogonal Frequency Division Multiple Access)
WiMax (Worldwide Interoperability for Microwave Access)/ LTE (Long Term Evolution for 3G )
Based on an all-IP packet switched network
VoIP(Voice over Internet Protocol )
Peak data rates up to 100 Mbps for high mobility and 1Gbps for low mobility.
LTE networks in Universiade Shenzhen: 50Mbps
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1. Wireless mobile communication
Challenges in future wireless communications
Scarcity of
radio frequency
Scarcity of
radio frequency
Low spectrum utilizationLow spectrum utilization Heterogeneous networksHeterogeneous networks
Increasing demand for spectrum
Increasing demand for spectrum
Problems in future wireless networksProblems in future wireless networks
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1. Wireless mobile communication
We should have a technology that can solve the scarcity of available spectrum
can satisfy the increasing spectrum requirement for wireless service
and can communicate seamlessly over the heterogeneous networks
CR(Cognitive Radio) and CRN(Cognitive Radio
Networks) are proposed…
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2. Introduction to CRNs
CR is defined as a radio that can change its transmitter parameters according to the interactions with the environment in which it operates.
SDR Cognitive Radio Cognitive Radio Networks
CR is based on the platform of software definition radio(SDR) which can easily reconfigure itself without changing any hardware.
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2. Introduction to CRNs
Features of CR Cognitive capability
Detect the spectrum holes and occupy the spectrum to enhance the data rate and spectrum utilization
Support seamless handoff to optimize the performance among the heterogeneous networks of GSM, WiMax, LTE…
Reconfigurability Dynamically change the transmitter frequency, power and
modulation parameters to adapt to the environment
CR is a hot research issue and faced with a lot of challenges.
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2. Introduction to CRNs
Challenges of CR
Cognition Information Detection Spectrum Sensing
Cognition Information Processing and Decision Dynamic spectrum management
Radio Resource Management
Reconfigurable Protocols
System architecture of CRNs
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3. Dynamic spectrum management
Scarcity of spectrum vs. low spectrum utilization
DSM(Dynamic Spectrum Management ) is proposed to enhance the spectrum utilization
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3. Dynamic spectrum management
DSM vs. FSM (Fixed spectrum management )
DSM vs. FSM
Dynamic spectrum allocation and sharing
Optimize the spectrum utilization
Maximize the system capacity
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3. Dynamic spectrum management
Steps for DSM Spectrum sensing:
detect the spectrum holes
Spectrum decision: model for choose the best available spectrum channel
Spectrum sharing: share the spectrum with primary users
Spectrum mobility: leave the channel occupied and find another suitable channel for communication
Primary user; Cognitive user; Spectrum holes
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3. Dynamic spectrum management
Challenges in research of DSM: spectrum decision, wideband spectrum sensing, QoS awareness, seamless handoff, hardware support...
Interference mitigation is one of the most important challenges for research.
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4. Interference Mitigation
Interference Scenarios Interference between primary users and
cognitive users It’s difficult to detect the status of PUs, So it may
interfering PUs when they occupy the spectrum again.
Interference among cognitive users When several CUs access the spectrum holes of
one PU, there exists interference among CUs.
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4. Interference Mitigation
Coloring graph model
PU: Ⅰ~Ⅳ
CU: 1~5
Channels: A,B,C
Interference range of PUs
Interference of CUs
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4. Interference Mitigation
Interference mitigation between PUs and CUs
If the CU is in the interference range of a PU, the CU can’t use the channel which the PU is occupied.
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4. Interference Mitigation
Interference mitigation among CUs
If there exists interference between CUs, there exists an edge between them and they can’t use a channel simultaneously.
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4. Interference Mitigation
Interference graph and coloring model
Coloring: Taking the each channel as one color, then color the vertexes with available colors, and the neighbor vertex can’t be colored with one color.
A
CB
CC
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4. Interference Mitigation
Spectrum allocation algorithms Greedy algorithm: maximize the spectrum
utilization Fair algorithm: maximize the fairness among
cognitive users Random algorithm: lower complexity and time
delay
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5. Summary
The development of wireless mobile communications
The advances of cognitive radio networks
Challenges in dynamic spectrum management
Coloring graph based interference mitigation
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Thank you!
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