Utility Based Scheduling in Cognitive Radio Networks

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Utility Based Scheduling in Cognitive Radio
Networks

• Term Project
• CmpE-300 Analysis of Algorithms
• Spring 2009
• Computer Engineering,
• Bogaziçi University, Istanbul

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Outline

• Wireless networks
• FDMA, TDMA, CDMA
• Dynamic Spectrum Access
• Cognitive Radio Networks
• Problem Formulation

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Cellular Networks
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Cellular Networks
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Cellular Networks

• MSC Mobile Switching Center
• How do different mobile stations communicate
  simultaneously with the BS?

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Frequency Division Multiple Access (FDMA)

• Each mobile device tunes to a frequency band
• Analogous to people talking in different rooms

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Frequency Division Multiple Access (FDMA)
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Time Division Multiple Access (TDMA)

• Each mobile device transmits data in a different
  time slot
• Analogous to people talking one by one
• GSM Combination of FDMA and TDMA
• 25 MHz bandwidth divided into 124 carrier
• frequencies of 200 KHz bandwidth
• Each carrier frequency divided into 8 time slots
• using TDMA
• 3G licenses
• Type-A 40 MHz, Turkcell
• Type-B 35 MHz, Vodafone
• Type-C 30 MHz, Avea

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Time Division Multiple Access (TDMA)
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Code Division Multiple Access (CDMA)

• Analogous to people talking in different languages

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Dynamic Spectrum Access (DSA)

• PROBLEM Underutilized spectrum resources due to
  fixed assignment strategy
• IDEA Utilizing white spaces in the spectrum
  without disturbing licensed users 1
• CHALLENGE
• Sensing the environment, detecting white spaces
• white spaces frequently change by time and
  space
• Changing radio parameters on the fly

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Frequency Allocation Charts

• In Turkey http//www.tk.gov.tr/Duzenlemeler/tekni
  k/marfl/_marfl1.asp

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White Space Concept
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Cognitive Radio (CR) Concept

• Initially proposed by Mitola 2
• Next step evolution of Software Defined Radio
  (SDR)
• Cognitive Radio (CR) Intelligent devices that
  can 2
• Sense and autonomously reason about their
  environment
• Adapt their communication parameters accordingly
• Realize DSA concept

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Terminology

• Primary User (PU)
• Licensed user
• Has exclusive rights for the spectrum
• Secondary User (SU)
• Unlicensed user
• Opportunistically utilizes the white spaces
• Has to vacate the spectrum band as soon as a PU
  appears
• Also called cognitive user

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IEEE 802.22 Network Architecture
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Research Problem

• totalNetworkUtility Total number of SUs that
  are satisfied in terms of throughput
• Maximize (totalNetworkUtility)
• subject to
• No interference is imposed on the PUs
• Reliable communication with the CBS is achieved
• No collisions occur among the SUs

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Research Problem Terminology

• N Total number of SUs
• F Total number of frequencies
• T Total number of time slots
• Uif Maximum number of packets that can be
  transmitted by user i to the CBS using frequency
  f
• (in a time slot)
• ti Throughput (data rate) of SU i
• g(ti)The level of satisfaction of SU i from
  throughput ti
• timin Minimum throughput required by SU i

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Problem Formulation

totalNetworkUtility
Each SU is assigned at least 1 time slot
At most 1 user is assigned a certain time slot
and frequency pair
Throughput of SU i
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Problem Formulation
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Problem Formulation
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References

• 1 Akyildiz, I., W. Lee, M. Vuran, and S.
  Mohanty, NeXt generation/dynamic spectrum
  access/cognitive radio wireless networks A
  survey, Computer Networks, Vol. 50, No. 13, pp.
  2127-2159, 2006.
• 2 Mitola, J., Cognitive Radio An
• Integrated Agent Architecture for
• Software Defined Radio, Doctor of
• Technology, Royal Institute of Technology
• (KTH), Stockholm, Sweden, 2000.

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• Questions?