1. Cognitive Radio: Opportunities and Challenges Dr Ying-Chang Liang Senior Scientist & Project Manager Institute for Infocomm Research (I 2 R) Singapore ycliang@i2r.a-star.edu.sg

2. Spectrum Scarcity due to Regional Coordination Requirement – Singapore Scenario Ch5Ch6Ch7Ch8Ch9 TV Channels used in SG Indonesias Batam TVR1 Malaysias RTM TV2 To avoid interference in TV band with Malaysia and Indonesia, Singapore virtually looses 2/3 of the spectrum! Ch10Ch11Ch12 Spectrum Allocation in broadcasting spectrum (174 MHz – 230 MHz)

3. Spectrum Measurement: 174 MHz – 230 MHz

4. White Spaces Everywhere M. Habibul, et al, Spectrum Survey in Singapore: Occupancy Measurements and Analyses, presented in CrownCom2008, May 15 – 17, 2008, Singapore < 5%

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, …

6. Spectrum Sharing in TV Band: 174 MHz – 230 MHz Ch5Ch6Ch7Ch8Ch9 TV Channels used in SG Indonesias Batam TVR1 Malaysias RTM TV2 Wireless Microphone Channels used in SG DAB Channels used in SG Ch10Ch11Ch12 Spectrum allocation in Singapore

7. 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) WRAN Repeater TV Transmitter WRAN Base Station Wireless MIC Wireless MIC WRAN Base Station : CPE : WRAN Base Station Typical ~33km Max. 100km Primary users: TV transmission, wireless MIC (microphone)

8. 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

9. 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

10. Remarks There are opportunities to explorespectrum 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!

11. 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!