cognitive wireless communications -a solution for

March 28, 2010

Cognitive Wireless Communications

-A Solution for Efficient Multiple

Networks Coexistence

Wenhui Xiong, Jun Wang & Wanbin Tang

National Key Laboratory of Science and Technology on Communications

University of Electronic Science and Technology of China

1National Key Laboratory of Science and Technology

on Communications


Outlines

Multiple Networks Coexistence: Opportunities and

Challenges


Components

Key Technologies

Dynamic Spectrum Sharing Network (DySNet): A

developing prototype for Cognitive Wireless

Communication system

2

Multiple Networks Coexistence: Opportunities and Challenges

More and more wireless services arise in recent years.

National Key Laboratory of Science and Technology on Communications 3

Mobile

Telephone

• 1990s, 1G/2G

• Voice and SMS only

Mobile

Internet

• 2000s, 2G/3G

• Voice, SMS, MMS, email,

Web, ……

Mobile

Multimedia

Mobile

?

• 2020s

• wireless in everything

• Ubiquitous service..

• 2010s, 3G/4G

• Voice, SMS, MMS, email,

Web, TV, VoD……


Problems: Multiple networks coexistence incurs resource scarcity.

Opportunities: resource can be shared among networks to improve efficiency.


WLAN

WLAN

APWLAN

AP

2G 3G IMT-ASenorSatellite

Core Network

Wireless Access Networks: Multiple

Networks Coexistence

logistics disaster heath agriculture security military others

Ubiquitous Services

http://www.circuitcity.com/detail.jsp?c=1&b=g&catoid=-8024&qp=0&bookmark=bookmark_3&oid=70600


(Cont.)

Opportunities Analysis

GSM: 955MHz-960MHz (24hours) IS-95: 869MHz-881MHz (24hours)

There exist great opportunities to share

resource among networks.

To utilize the potential opportunities, it is

necessary to meet the requirements of

primary networks.

5-Apr-11National Key Laboratory of Science and Technology on

Communications 66National Key Laboratory of Science and Technology on

Communications


Challenges (Cont.)

Cognitive Wireless Communications is an efficient solution for

multiple networks coexistence scenarios.


Communications

Radio propagation

environment

Intra-network

enviroment

Inter-network

enviroment

Modulation, Coding and

Multiple antennas

Multiple access and

multiple user detection

Channel

fading

Multi-user

interference

Unstable

transmission

Problem Solution

Cognitive Wireless

Communications

Link level

Single

Network

Multiple

network

conexistence

7National Key Laboratory of Science and Technology on

Communications


Challenges (Cont.)

There exists paradox of “transmission opportunities ” and “transmission

interruption” for resource sharing under multiple networks coexistence

scenarios.

8

Transmission

Opportunities：A new

network can provide

wireless services by

dynamically sharing

resource with the existing

networks to improve the

utilization efficiency of

resource.

Transmission Interruption：

A network can be

interrupted by the existing

networks due to their

reclaiming resource. Transmission

Interruption

Transmission

Opportunities


Communications 8National Key Laboratory of Science and Technology on

Communications


Outlines


Challenges


Components

Key Technologies


developing prototype

5-Apr-11 99National Key Laboratory of Science and Technology on

Communications



The Cognitive Wireless Communication System intelligently

find and utilize existing available resources to provide services.

Fundamental Characteristics

Environment Sensing and Prediction

Environment Adaptation

System Reconfiguration

Environment Information

Sensing and PredictionEnvironment Adaptation

System Reconfiguration

Cognitive Wireless Communications: Components

System Components

Opportunities Finding: find the available resource

independently or cooperatively

Opportunities Utilization: efficiently use the resource to

provide wireless service


Opportunities

Finding

Opportunities

Utilization

Sensing Based

Method

Cross-layer based

method

Opportunities Finding: Sensing Based Method


• Low received SNR at the cognitive receiver due tochannel shadow and fading;

• IEEE 802.22 requires to achieve 90% detection at10% false alarm rate when the SNR is as low as -20dB.

Low

SNR

• Sense the environment as quickly as possible to;

• Monitor the primary network’s activity and vacatethe spectrum as fast as possible when the primarynetwork reactivates

• IEEE 802.22 requires the sensing period less than200ms.

Speed

Sensing: Stochastic Resonance Based Sensing

Basic principle

The output SNR can be enhanced when proper noise is added

into the nonlinear system;

In the field of signal detection, the SR effect has been studied

to improve the signal detectability

System model


A/DNonlinear system/

nonlinear detector

( )x t ( )x k

SR noise n

( )y k detection

SR detector

Stochastic Resonance Based Sensing: Local Sensing

Results


1000 1500 2000 2500 3000 3500 40000

0.2

0.4

0.6

0.8

1

1.2x 10

-3

energy

p.d

.f

H0

H1

3000 4000 5000 6000 7000 8000 90000

1

2

3

4

5

6

7

8x 10

-4

energy

p.d

.f

H0

H1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Pf

Pd

no SR

SR

-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 00.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

SNR

pd

no SR

SR

-15 -10 -50

2000

4000

6000

8000

10000

12000

14000

16000

18000

SNR (dB)

the

num

be

r of sam

ple

s

no SR

SR

Sensing performance can be significantly improved!

Opportunities Utilization: A Cross layer based method

Challenges of Opportunities utilization

It possible to sense several channels;

Transmission rate and collision determines the

throughput;

The time-varying nature of the radio and network

environment poses a complicated task for adaptive

access and transmission techniques


The solution to above problems asks for cross-layer design

between physical layer and upper layer.


Outlines


Challenges


Components

Key Technologies


developing prototype

16

DysNet: a developing prototype

17

TV Tower

UE1 UE2 UE4 UE5 UE6

AP1 1 AP2 2Resource Sever

UE3 3

TV Program

TV Tx Controller

Control Center

FTP/Video Sever

TV Receiver

Internet

3G 3G 3G 3G 3G

3G

3G


CH1

CH2

CH3

3 available channels

Video

FTPVoIP

3 types of service

DysNet: a developing prototype

18National Key Laboratory of Science and Technology on Communications

DysNet: Spectrum Sensing

Turn off the TV transmission, and demo the

single/cooperative sensing

19

AP

1

UE

1

UE2 UE3

JRRM

TV tower

AP

2

UE4 UE5 UE6

CH1 CH2 CH3

Operation: Turn off the TV

transmission on CH1,CH2

& CH3

CH1 CH2

CH3CH1 CH2 CH3 CH1 CH2 CH3 CH1 CH2 CH3

CH1 CH2 CH3

CH1 CH2 CH3 CH1 CH2 CH3

CH1

CH2

CH3


DysNet: Dynamic Access

Dynamically Provides services to CRUs as the TV transmission are turned off

Step 1: 1 unused TV channel;

Step 2: increase the no. of unused channel to be 2;

Step3: turn off TV transmission on all 3 channels

As the no. of CRUs increases, the peak data rate increases

20

AP

1

CH1 CH3

Video

CH1

CH2

Video

CH2

1.CH1 unused

CH12.CH1，CH2

unused

CH2

CH13. CH1，CH2,CH3

unusedCH3

FTP


UE1 UE2 UE3

JRRM TV tower

DysNet: Resource Management

Provide Prioritized service to CRUs

Turn off low priority users’ transmission to provide service for high priority users

Resume service for low priority users when interference disappears

21

CH1 CH3Strong Interference at CH3

Video Video

CH1CH3

Video

CH3

Interference disappearCH3

FTP

CH2

Priority: UE2>UE3>UE1

Channel: CH1，CH2，CH3

AP

1

TV tower


UE1 UE2 UE3

JRRM

Summary

New services demand more & more spectrum

resources;

Spectrum is a scare resource;

Technical Challenges to make the cognitive wireless

network work:

Spectrum sensing—fast and reliably sense the radio

environment;

Spectrum utilization—efficiently use the available resource


cognitive wireless communications -a solution for

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