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How bad is selfish routing

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How bad is selfish routing Powered By Docstoc
					     Azin Dastpak

    August 2010
Simon Fraser University
   Introduction
   Definition
   Cognitive radio network architecture
   Cognitive radio systems
   Spectrum sharing in cognitive radio networks
   Game theoretical overview of spectrum
    sharing
   References
1
   Current wireless networks are regulated by
    fixed spectrum assignment policy.

   According to Federal Communication
    Commission, temporal and geographical
    variations in the utilization of the assigned
    spectrum ranges from 15% to 85%.
    Fixed Spectrum Assignment policy      spectrum white
                                              spaces


       Inefficient spectrum utilization

   Cognitive radio network is :
    ◦ A new paradigm that provides the capability to
      share or use the spectrum in an opportunistic
      manner.
2
   Cognitive radio is a wireless communication
    system which is aware of the environment
    and its changes and can adapt its
    transmission parameters accordingly.
    ◦ Cognitive Capability: The ability to sense the unused
      spectrum at a specific time and location (spectrum hole)

    ◦ Reconfigurability: The ability to receive and transmit at
      different frequency band enables the cognitive radio to
      reconfigure its parameters and select the best band.
3
   Primary network
    ◦ Primary users:
         Primary users have the license to operate in certain spectrum bands
    ◦ Primary base station:
       Controls the access of primary users to spectrum


   Secondary network
    ◦ Secondary users:
         Secondary users have no licensed bands assigned to them.
    ◦ Secondary base-station:
       A fixed infrastructure component with cognitive radio capabilities and
        provides single hop connection to secondary users.
    ◦ Spectrum broker :
       Scheduling server shares the spectrum resources between different
        cognitive radio networks.
   CR Network Access:          CRs can access their own base
    station on both licensed and unlicensed spectrum bands


   CR Ad Hoc Access:       CRs can communicate with other
    CRs through an ad hoc connection on both licensed and
    unlicensed spectrum bands.


   Primary Network Access :           CRs can access primary
    base station through the licensed bands.
3
   Spectrum sensing:        Cognitive radio user has the ability to
    sense the unused spectrum at any time and location.
   Spectrum management:               Based on the availability of
    the spectrum and other policies, CR user allocates the best
    available spectrum band.
   Spectrum mobility:          CR user shall vacate the spectrum in
    the presence of any primary user and move to next best available
    spectrum band
   Spectrum sharing: CR network has to provide a fair and
    optimal spectrum allocation method among multiple CR users.
 Interference avoidance
 QOS awareness
 Seamless communication




       Requires a cross layer design
   Physical layer:
    ◦ spectrum sensing
    ◦ data reconfigurable transmission based on Software
      Defined Radio (SDR).


   Link Layer :
    ◦ spectrum analysis
    ◦ spectrum selection(spectrum adjustment)
    ◦ spectrum coordination.
   MAC layer:
    ◦ Obtaining information on channel occupancy.

    ◦ Performing negotiation among primary users and secondary
      users for spectrum allocation and also among secondary
      users for channel sensing and access.

    ◦ Synchronizing transmission parameters (e.g. channel, time
      slot) between transmitter and receiver.

    ◦ Facilitating spectrum trading functions (e.g. spectrum
      bidding and pricing).
   Static cognitive radio system:           Secondary user
    observes the activity of the primary users in a fixed spectrum
    band and access the entire spectrum band if it senses the
    opportunity. Can be built on the following standards:
    ◦ 802.11
    ◦ 802.15
    ◦ 802.3

   Dynamic cognitive radio system:             Secondary users
    can transmit using different bandwidths by changing the
    transmission parameters in the physical layer (based on
    OFDM or MC-CDMA).
   The first IEEE standard utilizing cognitive radio (CR)
    technology to exploit the television white space.

   The focus was on building fixed point-to-
    multipoint WRAN that utilizes UHF/VHF TV bands
    between 54 and 862 MHz.
   Leased network

   Cognitive mesh network

   Emergency network

   Military network
4
   Spectrum sensing: The secondary user can only
    allocate a spectrum if it’s not used by an unlicensed
    user.

   Spectrum allocation: Allocation of a channel not
    only depends on spectrum availability but also depends
    on internal and external policies.

   Spectrum access: Since there are multiple
    secondary users trying to access the spectrum, their
    access should be coordinated to avoid colliding in
    overlapping portions of the spectrum
   Transmitter-receiver handshake: After deciding a
    portion of the spectrum, the receiver of this communication
    should also be indicated.

   Spectrum mobility: If the specific portion of the spectrum
    is needed by a licensed user, the communication needs be
    continued in another vacant portion.
   Architecture:
    ◦ Centralized : The spectrum allocation and process are
      controlled by a central entity.


    ◦ Distributed : Spectrum allocation and access are
      based on local or global policies that are performed by
     each node distributively.


        distributed solutions closely follow the
     centralized solutions but they have the extra
       cost of message passing between nodes.
   Spectrum Allocation behavior:
    ◦ Cooperative Spectrum sharing : The effect of the communication of
      one node on other nodes in considered.

       Closely reach global optimum.
       Result in fairness and improved throughput.


    ◦ Non-cooperative Spectrum Sharing : Only a single node is
      considered.

       As the interference in other CRs are not considered this solution may result in
        reduced spectrum utilization.
       They don’t need frequent message passing as in cooperative solutions
       Energy consumption
   Spectrum access technique:
   Overlay spectrum sharing: Portion of the spectrum can be accessed
    that has not been used by licensed users.

   Underlay spectrum sharing: Transmission of a CR node is regarded as
    noise by licensed users.
   Scope:
    ◦ Intra-network Spectrum Sharing: Spectrum
     allocation between the entities of a CR network. The
     users of a CR network try to access the available
     spectrum without causing interference to the primary
     users.


    ◦ Inter-network Spectrum Sharing: This setting
     enables multiple systems to be deployed in
     overlapping locations and spectrum.
5   Game theoretical overview of dynamic spectrum sharing
   The behavior of the cognitive radios in
    dynamic spectrum access networks can be
    modeled as a dynamic spectrum sharing
    game (DSSG).
    Non-cooperative DSSG without centralized
    control
    ◦     The focus is on distributed design and cooperation
        simulation.
   Cooperative DSSG
    ◦ users do enforceable spectrum sharing through
      centralized authorities. Nash bargaining Solution plays
      an important role in cooperative games.

    Negotiated or leasing-based dynamic spectrum
    sharing
    ◦ This scenario can be modeled as multiplayer non-
      cooperative game with incomplete information. Auction
      theory is applied to formulate and analyze the
      interactions.
   Local Bargaining
    ◦ The product of user throughput is considered the
      optimization goal of local bargaining
   Repeated Spectrum Sharing Game Model
    ◦     A similar static game is played many times. It
        gives the observers the opportunity to make
        decision based on past moves. One of the most
        important results in repeated game theory is Folk
        Theorem.
   Auction-Based Spectrum Sharing Game
    ◦ VCG is usually used to achieve socially optimal solution

    ◦ It may not be suitable for spectrum sharing because of
      the temperature-constraint, information overhead and
      computational burden.

    Two other auctions are generally used:

    ◦ SINR Auction: charging secondary users according to
      their received signal-to-interference-plus-noise ratio.
    ◦ Power Auction: charging secondary users based on their
      received power
   Belief-Assisted Pricing
    ◦ To achieve efficient pricing distributively in DSSGs
      with incomplete information, the belief metrics are
      proposed to predict other user’s future possible
      strategies according to the game histories and
      assist each user’s decision making.
The spectrum sharing needs to be efficient and fair
 Price of Anarchy
    ◦ In non-cooperative DSSG without centralized authorities, the
      interactions between selfish users may lead to an inefficient Nash
      Equilibrium
    ◦ The price of anarchy is an important measure.

   Nash Bargaining Solution in Spectrum Sharing Games
    ◦ To achieve fair and efficient dynamic spectrum sharing, NBS is an
      important optimality analysis.
   Dynamic Programming for DSSGs:
    ◦ In one case the Bellman equation can be applied to represent each
      secondary user’s payoff in the form of summation of two terms
          1. it’s current pay off based on current spectrum sharing states.
          2. it’s expected future payoff based on the updated spectrum sharing
          state.
6   References
   [1] I. Akyildiz, 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] L. Hu, V. Iversen, and L. Dittmann, “Survey of PHY and LINK Layer Functions of
    Cognitive Radio Networks for Opportunistic Spectrum Sharing,” Communications
    and Networking in China, pp. 10–24, 2009.
   [3] Y. Xiao and F. Hu, Cognitive radio networks. Auerbach Publications, 2008.
   [4] I. Akyildiz, W. Lee, M. Vuran, and S. Mohanty, “A survey on spectrum
    management in cognitive radio networks,” IEEECommunications Magazine, vol. 46,
    no. 4, pp. 40–48, 2008.
   [5] Y. Yi, J. Zhang, Q. Zhang, T. Jiang, and J. Zhang, “Cooperative Communication-
    Aware Spectrum Leasing in Cognitive Radio Networks,” in 2010 IEEE Symposium
    on New Frontiers in Dynamic Spectrum, 2010, pp. 1–11.
   [6] Z. Ji and K. Liu, “Cognitive radios for dynamic spectrum access-dynamic
    spectrum sharing: A game theoretical overview,” IEEE Communications Magazine,
    vol. 45, no. 5, pp. 88–94, 2007.
   [7] L. Chen, S. Iellamo, M. Coupechoux, P. Godlewski, P. da Vinci, and I. Milan, “An
    Auction Framework for Spectrum Allocation with Interference Constraint in
    Cognitive Radio Networks.”

				
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