Cognitive Radio: Opportunities and Challenges

Dr Ying-Chang Liang

Senior Scientist & Project Manager

Institute for Infocomm Research (I2R)

Singapore

ycliang@i2r.a-star.edu.sg

Spectrum Scarcity due to Regional Coordination Requirement – Singapore Scenario

Ch5 Ch6 Ch7 Ch8 Ch9

TV Channels

used in SG

Indonesia’sBatam TVR1

Malaysia’sRTM TV2

To avoid interference in TV band with Malaysia and Indonesia,

Singapore virtually looses 2/3 of the spectrum!

Ch10 Ch11 Ch12

• Spectrum Allocation in broadcasting spectrum (174 MHz – 230 MHz)

Spectrum Measurement: 174 MHz – 230 MHz

Broadcasting

Ch 5

175 180 185 190 195 200 205 210 215 220 225 230-120-100-80-60-40-20

Freqeuency (MHz)

Pow

er (

dBm

)

175 180 185 190 195 200 205 210 215 220 225 23006:00h

12:00h

18:00h00:00h

06:00h

Frequency (MHz)

Tim

e In

stan

ts

175 180 185 190 195 200 205 210 215 220 225 2300

0.5

1

Frequency (MHz)

Dut

y C

ycle

threshold =-98.9 dBm

averageduty cycle= 0.4905

Ch 6 DAB Ch 8 Ch 9 Ch 10 Ch 11 Ch 12

White Spaces Everywhere

M. Habibul, et al, Spectrum Survey in Singapore: Occupancy Measurements and Analyses, presented in CrownCom’2008, May 15 – 17, 2008, Singapore

< 5%

Opportunities: Cognitive Radio to Improve the Spectrum Utilization Efficiency

• Opportunistic Spectrum Access– Based on on/off activity of

the primary users

• Spectrum Sharing – Based on interference

temperature– The secondary users co-

exist with the primary users

PU-Tx

PU-Rx

SU-Tx

SU-Rx

Different cognition levels: on/off status, interference temperature, …

Spectrum Sharing in TV Band:174 MHz – 230 MHz

Ch5 Ch6 Ch7 Ch8 Ch9

TV Channels

used in SG

Indonesia’sBatam TVR1

Malaysia’sRTM TV2

Wireless Microphone

Channels used in SG

DAB Channels

used in SG

Ch10 Ch11 Ch12

Spectrum allocation in Singapore

Opportunistic Spectrum Access: IEEE802.22 Wireless Regional Area Networks (WRAN)

• Reuse the unused or under-utilized TV bands (54MHz – 862MHz) for broadband wireless access– Co-exist with higher priority users (TV, wireless microphones)

집

집

집

집집

집

집

집

집

집 집

집

집

WRANRepeater

TV TransmitterWRAN

Base Station

WirelessMIC

집

WirelessMIC

집

WRANBase Station

집

집

: CPE집

집

집

집

집

집

: WRAN Base Station

집

집

집

집

집

집

집

집

집

집

집

집

집

Typical ~33kmMax. 100km집 집

집집 집

집

집

집

Primary users: TV transmission, wireless MIC (microphone)

Challenges in Spectrum Sharing

• Is low power transmission for secondary users sufficient?– How low should it be?

• Effective ways to estimate interference power received at primary users– Innovative mechanisms are needed

especially when primary user does not cooperate

PuTx

PuRx

SuTx

SuRx

Challenges in Opportunistic Spectrum Sharing

• Stringent spectrum sensing requirements– Various types of primary users

• e.g., 802.22: TV - 6/7/8MHz, Wireless microphone - 200 kHz (carrier not fixed)

– Low SNR environment • in 802.22, TV signals are to be detected at -20 dB SNR with 90%

detection of probability and 10% false alarm probability

– Fast wideband sensing– Robust sensing (to noise uncertainty, interference …)

• Can the acquired on/off status be used to protect primary users?– Channel asymmetry (fading, Tx/Rx duplex, …) – Shadowing, hidden terminal issue– Transmission power asymmetry

Remarks

• There are opportunities to explore “spectrum white spaces”

• To promote white space reuse (dynamic spectrum access)– technically, though challenging, effective

solutions are needed to protect the primary users

– economically, good business models are needed to make both primary users and secondary users happy!

Remarks• Cognitive radio -> cognitive radio networks

– How to acquire cognition• PHY sensing

• Network layer traffic sensing

– Cognitive MAC: Control information sharing, cooperation, …

– Distributed processing

– Other issues (security, trust, …)

• Let us work together to make cognitive radio (networks) from imagination to reality!