Cognitive Radio Networks
Zhu Jieming
Group Presentaion
Aug. 29, 2011
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Outline
1. Wireless mobile communication
2. Introduction to cognitive radio networks
3. Dynamic spectrum management
4. Interference mitigation
5. Summary
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1. Wireless mobile communication
The development of wireless mobile
communications
1G
2G
2.5G
2.75G
3G
4G
Directions for development
High
data rate
Broadband
Heterogeneity
Ubiquity
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1. Wireless mobile communication
1G
2G
2.5G
2.75G
3G
4G
1G:
 Analog mobile phone
 FDMA (Frequency Division Multiple Access)
 Low system capacity
and security problems
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1. Wireless mobile communication
1G
2G
2.5G
2.75G
3G
4G
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
1G
2G
2.5G
2.75G
3G
4G
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
1G
2G
2.5G
2.75G
3G
4G
3G:
 CDMA (Code Division Multiple Access)
 Data Rate: 2.4Mbps
3G
Standards
• WCDMA (Europe)
• CDMA2000 (America)
• TD-SCDMA (Datang, China)
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1. Wireless mobile communication
1G
2G
2.5G
2.75G
3G
4G
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
Problems in future wireless networks
Scarcity of
radio frequency
Low spectrum utilization
Increasing demand
for spectrum
Heterogeneous 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 )
Dynamic spectrum
allocation and sharing
DSM
vs.
FSM
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
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simultaneously.
4. Interference Mitigation
 Interference graph and coloring model
C
A
C
C
B
 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.
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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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