COGNITIVE RADIO

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COGNITIVE RADIO

• TECHNICAL SEMINAR
• Presented by
• Sangeetha Nandan (1ay05cs057)

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INTRODUCTION

• Cognitive radio is a paradigm for wireless
  communication in which either a network or
  a wireless node changes its transmission or
  reception parameters to communicate efficiently
  avoiding interference with licensed or unlicensed
  users. This alteration of parameters is based on
  the active monitoring of several factors in the
  external and internal radio environment, such as
  radio frequency spectrum, user behavior and
  network state.

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ARCHITECTURE OF CR
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A. Physical Layer Functions

• 1) Spectrum Sensing The main function of the
  physical layer is to sense the spectrum over all
  available degrees of freedom (time, frequency and
  space) in order to identify sub-channels
  currently available for transmission.

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2) Channel Estimation

• In order to set up the link, channel sounding is
  used to estimate the quality of sub-channels
  between SUs that want to communicate. The
  transmission parameters (transmit power, bit
  rate, coding, etc.) are determined based on the
  channel sounding results

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3) Data Transmission

• CRs optimally uses the available spectrum as
  determined by the spectrum sensing and channel
  estimation functions. Therefore it should have
  the ability to operate at variable symbol rates,
  modulation formats (e.g. low to high order QAM),
  different channel coding schemes, power levels
  and be able to use multiple antennas for
  interference nulling, capacity increase (MIMO) or
  range extension

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B. Link Layer Functions

• Group Management
• It is assumed that any secondary station will
  belong to a SU Group. A newly arriving user can
  either join one of the existing groups or create
  a new one through the Universal Control Channel.
• Link Management
• covers the setup of a link in order to enable the
  communication between two SUs and afterwards the
  maintenance of this SU Link for the duration of
  the communication.
• Medium Access Control
• As long as it can be assured that all
  Sub-Channels are used exclusively, i.e. all
  Sub-Channels used by one SU Link cannot be used
  by any other SU Link this problem comes down to a
  simple token-passing algorithm ensuring that only
  one of the two communication peers is using the
  link.

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Types of Cognitive Radio

• Depending on the set of parameters taken into
  account in deciding on transmission and reception
  changes, we can distinguish certain types of
  cognitive radio.
• The main two are
• Full cognitive radio
• Spectrum sensing cognitive radio

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(Contd.)

• depending on the parts of the spectrum available
  for cognitive radio, we can distinguish
• Licensed Band Cognitive Radio (IEEE
  802.22)
• Unlicensed Band Cognitive Radio (IEEE
  802.15)

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FUNCTIONS OF CR

• The main functions of Cognitive Radios are
• Spectrum Sensing
• detecting the unused spectrum and sharing it
  without harmful interference with other users.

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(Contd.)

• Spectrum sensing techniques can be classified
  into three categories
• Transmitter detection cognitive radios must have
  the capability to determine if a signal from a
  primary transmitter is locally present in a
  certain spectrum, there are several approaches
  proposed
• matched filter detection
• energy detection
• cyclostationary feature detection

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Match filter detection

• is obtained by correlating a known signal, or
  template, with an unknown signal to detect the
  presence of the template in the unknown signal.

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(Contd.)

• Cooperative detection refers to spectrum sensing
  methods where information from multiple Cognitive
  radio users are incorporated for primary user
  detection.

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(Contd.)

• Spectrum Management Capturing the best available
  spectrum to meet user communication requirements
• management functions can be classified as
• spectrum analysis
• spectrum decision

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(Contd.)

• Spectrum Mobility is defined as the process
  when a cognitive radio user
  exchanges its frequency of operation. Cognitive
  radio networks target to use the spectrum in a
  dynamic manner by allowing the radio terminals to
  operate in the best available frequency band,
  maintaining seamless communication requirements
  during the transition to better spectrum .

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(Contd.)

• Spectrum Pooling is a resource sharing strategy
  that organizes the available spectrum into a
  spectrum pool which is then optimized for a given
  application . Once a primary user appears,
  secondary users need to cease transmission if
  they will cause interference.

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Cognitive radio network

• The cognitive radio network is an intelligent
  multi user wireless communication system that
  embodies the following list of primary tasks
• to perceive the radio environment (i.e., outside
  world) by empowering each users receiver to
  sense the environment on a continuous-time basis
• to learn from the environment and adapt the
  performance of each transceiver

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(Contd.)

• to facilitate communication between multiple
  users through cooperation in a self-organized
  manner
• to control the communication processes among
  competing users through the proper allocation of
  available resources

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Software defined radio

• Software-Defined Radio (SDR) system is a radio
  communication system where components that have
  typically been implemented in hardware (e.g.
  mixers, filters, amplifiers, modulators/demodulato
  rs, detectors. etc.) are instead implemented
  using software on a personal computer or other
  embedded computing devices.

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(Contd.)

• A basic SDR may consist of a computer (PC)
  equipped with a sound card, or other
  analog-to-digital converter, preceded by some
  form of RF front end. Significant amounts of
  signal processing are handed over to the general
  purpose processor, rather than done using
  special-purpose hardware. Such a design produces
  a radio that can receive and transmit a different
  form of radio protocol (sometimes referred to as
  a waveform) just by running different software.
  It is the enabler of Cognitive radio.

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Functions provided by SDRs

• 1. The radio hardware. The radio hardware
  includes radio frequency circuitry and signal
  processing devices.
• 2. Software modules. Software modules represent
  code that has been loaded into field programmable
  gate arrays (FPGAs), digital signal processors
  (DSPs), or embedded general purpose processors.

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(Contd.)

• 3. Middleware. The middleware layer attempts to
  reduce the details of specific devices and
  software modules to common abstractions.
• 4. Device Manager The device manager loads radio
  configurations into the hardware components and
  sets-up the logical radios.

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(Contd.)

• 5. Logical Radio Layer Depending on the radio
  configuration, the hardware and software can be
  programmed to act like multiple radio links .
• 6. Module Libraries The module libraries are
  collections of radio functions.

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(Contd.)

• 7. Rules Engine and Policies Policies are used
  to limit the operation of the radio due to
  regulatory, geographical, or physical
  constraints.
• 8. Smart Controller A smart controller manages
  all of the radio resources outlined above.

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ISSUES IN CR

• Spectrum management
• Spectrum utilization presence of white spaces
• Spectral co-existence
• Spectrum sharing

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Spectrum management

• spectrum management involves assigning particular
  frequencies to specified users. This can be done
  through administrative methods or by means of a
  market process, such as an auction. Additionally,
  some spectrum may be reserved for unlicensed use
  (this is sometimes referred to as the spectrum
  commons). All users satisfying certain
  restrictions, for example on power levels, might
  have access to unlicensed bands.

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Spectral utilization

• white spaces refer to frequencies allocated to a
  broadcasting service but not used locally
• unlicensed devices that can guarantee that they
  will not interfere with assigned broadcasts can
  use the empty white spaces in spectrum

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Spectral coexistence

• Two approaches have been given
• Collaborative approach radio of different
  technologies exchange information regarding the
  frequency usage of the spectrum.
• Non collaborative radio devices sense the
  frequency spectrum occupancy and determine by
  itself the channel definition without
  communicating with other users.

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Spectral sharing

• Stringent spectrum sensing requirements
• Various types of primary users
• Low SNR environment
• Fast wideband sensing
• Robust sensing (to noise uncertainty,
  interference )
• Can the acquired on/off status be used to protect
  primary users?
• Channel asymmetry
• Shadowing, hidden terminal issue
• Transmission power asymmetry

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CONCLUSION

• There are opportunities to explore spectrum
  white spaces
• To promote white space reuse
• 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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(Contd.)

• 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!

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(Contd.)

• Cognitive radio can be used in the following
  fields
• Signal processing
• Communication theory
• Radar systems
• Control theory

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bibliography

• Wikipedia.org
• IEEE xplore
• www.technologyreview.com
• www.cognitiveradio.wireless.vt.edu
• IEEE papers

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• THANK YOU