Cognitive Radio: Opportunities and Challenges

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Cognitive Radio Opportunities and Challenges

• Dr Ying-Chang Liang
• Senior Scientist Project Manager
• Institute for Infocomm Research (I2R)
• Singapore
• ycliang_at_i2r.a-star.edu.sg

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Spectrum Scarcity due to Regional Coordination
Requirement Singapore Scenario

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

Indonesias Batam TVR1
Malaysias RTM TV2
Ch5
Ch6
Ch7
Ch8
Ch9
Ch10
Ch11
Ch12
TV Channels used in SG
To avoid interference in TV band with Malaysia
and Indonesia, Singapore virtually looses 2/3 of
the spectrum!
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Spectrum Measurement 174 MHz 230 MHz
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White Spaces Everywhere
lt 5
M. Habibul, et al, Spectrum Survey in Singapore
Occupancy Measurements and Analyses, presented
in CrownCom2008, May 15 17, 2008, Singapore
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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

Different cognition levels on/off status,
interference temperature,
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Spectrum Sharing in TV Band174 MHz 230 MHz
Indonesias Batam TVR1
Malaysias RTM TV2
Ch5
Ch6
Ch7
Ch8
Ch9
Ch10
Ch11
Ch12
DAB Channels used in SG
TV Channels used in SG
Wireless Microphone Channels used in SG
Spectrum allocation in Singapore
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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)

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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

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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

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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!

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Remarks

• Cognitive radio -gt 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!