Cognitive Radio: Opportunities and Challenges
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Transcript of Cognitive Radio: Opportunities and Challenges
Cognitive Radio: Opportunities and Challenges
Dr Ying-Chang Liang
Senior Scientist & Project Manager
Institute for Infocomm Research (I2R)
Singapore
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
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집집
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WRANRepeater
TV TransmitterWRAN
Base Station
WirelessMIC
집
WirelessMIC
집
WRANBase Station
집
집
: CPE집
집
집
집
집
집
: WRAN Base Station
집
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Typical ~33kmMax. 100km집 집
집집 집
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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!