Research Opportunities in Cognitive Radios

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Research Opportunities in Cognitive Radios

• Danijela Cabric
• Berkeley Wireless Research Center, UC Berkeley
• January 13th, 2004

Adapting behavior based on external factors
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Window of Opportunity

• Existing spectrum policy forces spectrum to
  behave like a fragmented disk
• Bandwidth is expensive and good frequencies are
  taken
• Unlicensed bands biggest innovations in
  spectrum efficiency

• Recent measurements by the FCC in the US show 70
  of the allocated spectrum is not utilized
• Time scale of the spectrum occupancy varies from
  msecs to hours

Frequency (Hz)
Time (min)
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Spectrum Sharing

• Existing techniques for spectrum sharing
• Unlicensed bands (WiFi 802.11 a/b/g)
• Underlay licensed bands (UWB)
• Opportunistic sharing
• Recycling (exploit the SINR margin of legacy
  systems)
• Spatial Multiplexing and Beamforming
• Drawbacks of existing techniques
• No knowledge or sense of spectrum availability
• Limited adaptability to spectral environment
• Fixed parameters BW, Fc, packet lengths,
  synchronization, coding, protocols,
• New radio design philosophy all parameters are
  adaptive
• Cognitive Radio Technology

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What is a Cognitive Radio?

• Cognitive radio requirements
• co-exists with legacy wireless systems
• uses their spectrum resources
• does not interfere with them
• Cognitive radio properties
• RF technology that "listens" to huge swaths of
  spectrum
• Knowledge of primary users spectrum usage as a
  function of location and time
• Rules of sharing the available resources (time,
  frequency, space)
• Embedded intelligence to determine optimal
  transmission (bandwidth, latency, QoS) based on
  primary users behavior

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Application Scenarios

Third party access in licensed networks
Licensed network
Cellular, PCS band Improved spectrum
efficiency Improved capacity
TV bands (400-800 MHz)
Non-voluntary third party access Licensee sets a
protection threshold
Unlicensed network
Secondary markets
ISM, UNII, Ad-hoc
Public safety band Voluntary agreements between
licensees and third party Limited QoS
Automatic frequency coordination
Interoperability Co-existence
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FCC Announcement

• Released on Dec 30th 2003, (ET Docket No. 03-108)
• Facilitating Opportunities for Flexible,
  Efficient, and Reliable Spectrum Use Employing
  Cognitive Radio Technologies
• We recognize the importance of new cognitive
  radio technologies, which are likely to become
  more prevalent over the next few years and which
  hold tremendous promise in helping to facilitate
  more effective and efficient access to spectrum
• We seek to ensure that our rules and
  policies do not inadvertently hinder development
  and deployment of such technologies, but instead
  enable a full realization of their potential
  benefits.

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BWRC Approach

• Channel and Interference Model
• Cognitive Radio Functions
• Algorithms
• Test Scenarios
• Cognitive Radio Architecture

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Channel and Interference Model

• Measurement of the spectrum usage in frequency,
  time, and space
• Wideband channel
• Common with UWB
• Spatial channel model
• Clustering approach
• Interference correlation
• Derive statistical traffic model of primary users
• Power level
• Bandwidth
• Time of usage
• Inactive periods

Angular domain
Frequency (Hz)
Time (min)
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Cognitive Radio Functions

• Physical Layer
• OFDM transmission
• Spectrum monitoring
• Dynamic frequency selection, modulation, power
  control
• Analog impairments compensation

• Sensing Radio
• Wideband Antenna, PA and LNA
• High speed A/D D/A, moderate resolution
• Simultaneous Tx Rx
• Scalable for MIMO

• MAC Layer
• Optimize transmission parameters
• Adapt rates through feedback
• Negotiate or opportunistically use resources

LNA
A/D
RF/Analog Front-end
Digital Baseband
MAC Layer
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Sensing Radio

• A/D converter
• High resolution
• Speed depends on the application
• Low power 100mWs
• RF front-end
• Wideband antenna and filters
• Linear in large dynamic range
• Good sensitivity
• Interference temperature
• Protection threshold for licensees
• FCC 2400-2483.5 MHz band is empty if
• Need to determine length of measurements

Spectrum usage in (0, 2.5) GHz
Measurement taken at BWRC
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Cognitive Radio Baseband Processing
PHY
MAC

• MCMA processing
• OFDM System
• Agile, efficient FFT
• Spatial processing
• Exploits clustered model
• Scalable with of antennas

• PHY adaptive, parametrizable
• MAC intelligent, optimization algos
• PHYMAC can be implemented on
• Software Defined Radios
• Reconfigurable Radios

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From WiFi to Cognitive Radios
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Test Scenario at 2.4 GHz, Indoor

• Unlicensed band 80 MHz bandwidth
• OFDM system (like 802.11a/g)
• Multiple antennas for interference avoidance and
  range extension
• Centralized approach through AP

Microwave oven
AP
802.11 b/g
Bluetooth
Dynamic Frequency Selection
Cordless phone
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Testbed for Wireless Experimentation

• BWRC infrastructure
• BEE Processing Units (4)
• 2.4 GHz RF Front-ends (32)
• Scalable multiple antenna transmission system

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Research Agenda

• Derive system specification from measurements
• Analog front-end specification and design
• Develop and implement algorithms for
• Sensing environment
• Dynamic frequency selection and adaptive
  modulation
• Transmit power control and spatial processing
• Interference cancellation in spatial domain
• Spectrum rental strategies
• Test algorithms in realistic wireless scenarios
• Design an architecture for a Cognitive Radio