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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!