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  • Integrated Communication Systems Group Ilmenau University of Technology

    Cognitive Radio Networks

    Mobile Communication Networks (RCSE) Winter Semester 2012/13

  • Integrated Communication Systems Group


    • Radio Allocation • Radio Flexibility and Capability • Spectrum Management • Cognitive Radio

    – Definitions – Architectures – Cognitive Cycle – Enabling technologies – Implementation – Standards – Applications

    • Summary

    Mobile Communication Networks (RCSE) 2

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    Spectrum Allocation

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    Spectrum Utilization

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    In Summary…

    • Spectrum scarcity is largely due to – Inefficient fixed frequency allocations and utilization rather

    than any physical shortage of spectrum • So, a new radio technology is needed with the following

    characteristics: – Flexibility – Reconfigurability – Awareness – Adaptability – Intelligence

    Mobile Communication Networks (RCSE) 5

  • Integrated Communication Systems Group

    Radio Flexibility and Capability

    • Software capable radio: – Fixed modulation capabilities – Small number of frequencies

    • Software Programmable radio: – Ability to add new functionality

    through software changes – Advanced networking capability

    • Software-Defined Radio: – Complete adjustability through

    software of all radio operating parameters

    Mobile Communication Networks (RCSE) 6

    • Aware Radio: – Radio that sense all or part of

    their environment • Adaptive Radio:

    – Radio that modify its operating parameters

    • Cognitive radio: – Radio is aware, adaptive and


    Software capable


    Software Programmabl

    e radio

    Software Defined


    Aware radio

    Adaptive radio

    Cognitive radio

    Increasing Technology/Software Maturity

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    Spectrum management

    Dynamic Spectrum Management: • Fair allocation of spectrum

    – Users with the same rights (Horizontal sharing)

    – Users with the different rights (Vertical sharing)

    • Centralized vs. Decentralized – Centralized Approach

    • Need for a center for collecting radio scene information

    • Globally optimal solution – Decentralized Approach

    • Utilization of self-organization principle

    • Scalable • Suboptimal

    Mobile Communication Networks (RCSE) 7

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    Spectrum management

    Mobile Communication Networks (RCSE) 8

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    Hierarchical Access Model

    • Spectrum Underlay – Secondary users (SUs) operate below the noise floor of primary users

    (PUs) – Short-range high data rate with extremely low transmission power – E.g. UWB

    • Spectrum Overlay – Investigated by the DARPA Next Generation (XG) program under the

    term opportunistic spectrum access (OSA) – SUs identify and exploit local and instantaneous spectrum availability

    in a nonintrusive manner

    Mobile Communication Networks (RCSE) 9

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    Cognition and cognitive radio

    10Mobile Communication Networks (RCSE)

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    Cognition, Cognitive radio and Cognitive networks

    Mobile Communication Networks (RCSE) 11


    Mobile device Cognitive


    Cognitive networks

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    What is a Cognition?

    • According to the Encyclopedia of Computer, three-point computational view of cognition is listed – Mental states and processes intervene between input stimuli and

    output responses – The mental states and processes are described by algorithms – The mental states and processes lend themselves to scientific


    • Pfeifer and Scheier: the interdisciplinary study of cognition is concerned with exploring general principles of intelligence through a synthetic methodology termed learning by understanding.

    Mobile Communication Networks (RCSE) 12

  • Integrated Communication Systems Group

    What is a Cognitive Radio?

    Definitions • Federal Communications Commission Definition: Cognitive radio is a radio that

    can change its transmitter parameters based on interaction with the environment in which it operates

    • Mitola Definition: Cognitive radio identifies the point at which wireless PDAs and the related networks are sufficiently computationally intelligent on the subject of radio resources and related computer-to-computer communications

    – to detect user communications needs as a function of use context, and – to provide radio resources and wireless services most appropriate to those needs

    • Simon Haykin Definition: Cognitive radio is an intelligent wireless communication system that is aware of its surrounding environment (i.e., outside world), and uses the methodology of understanding-by-building to learn from the environment and adapt its internal states to statistical variations in the incoming RF stimuli by making corresponding changes in certain operating parameters (e.g., transmit-power, carrier- frequency, and modulation strategy) in real-time, with two primary objectives in mind:

    – highly reliable communications whenever and wherever needed – efficient utilization of the radio spectrum

    Mobile Communication Networks (RCSE) 13

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    Spectrum Opportunity

    Spectrum opportunity: “A band of frequencies that are not being used by the PU of that band at a particular time in a particular geographic area”

    Mobile Communication Networks (RCSE) 14

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    Cognitive radio architecture

    15Mobile Communication Networks (RCSE)

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    Cognitive radio node architecture

    Mobile Communication Networks (RCSE) 16

    SDR transceiver





    C og

    ni tiv

    e en

    gi ne

    A da

    pt iv

    e pr

    ot oc


    Transmit/ receive

    Adaptive protocols: • Aware of the variations in the

    cognitive radio environment • consider the traffic activity of

    primary users • Consider the transmission

    requirements of secondary users, and variations in channel quality

    Cognitive engine: • Establishes interfaces

    among the SDR transceiver, adaptive protocols, and wireless applications and services

    • Uses intelligent algorithms

  • Integrated Communication Systems Group

    Cognitive Radio Network Architecture

    17Mobile Communication Networks (RCSE)

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    Cognitive Radio Network Architecture

    • Primary networks – Networks with access right to certain spectrum bands, e.g. common

    cellular systems and TV broadcast networks – Users of these networks are referred to as primary users. They have

    the right to operate in licensed spectrum – Users of certain primary network do not care of other primary or

    secondary networks users

    • Secondary networks – Do not have license to operate in the spectrum band they currently

    use or aim at using – Opportunistic spectrum access – Users of these networks are referred to as secondary users. They

    have no right to access licensed bands currently used – Additional functionalities are required to share licensed spectrum

    bands with other secondary or primary networks

    Mobile Communication Networks (RCSE) 18

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    Cognitive Cycle: Mitola

    Mobile Communication Networks (RCSE) 19

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    Cognitive Cycle: Akyildiz

    Spectrum Decision

    Spectrum Sharing

    Spectrum Sensing

    Spectrum Mobility

    Radio environment

    Spectrum characterizations

    RF stimuli

    Spectrum holeChannel


    Transmitted signal

    Decision request

    Primary user detection

    20Mobile Communication Networks (RCSE)

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    Spectrum Sensing

    21Mobile Communication Networks (RCSE)

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    Spectrum Sensing

    Mobile Communication Networks (RCSE) 22

    T. Yucek and H. Arslan “Survey of Spectrum Sensing Algorithms for Cognitive Radio Applications” IEEE Communications Surveys & Tutorials, Vol. 11, No. 1, First Quarter 2009

  • Integrated Communication Systems Group


    • Interference temperature measurement – Secondary users are aware of their locations and transmission power.

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