Azin Dastpak
August 2010
Simon Fraser University
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Introduction
Definition
Cognitive radio network architecture
Cognitive radio systems
Spectrum sharing in cognitive radio networks
Game theoretical overview of spectrum
sharing
References
1
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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
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Cognitive radio network is :
◦ A new paradigm that provides the capability to
share or use the spectrum in an opportunistic
manner.
2
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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.
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Primary network
◦ Primary users:
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Primary users have the license to operate in certain spectrum bands
◦ Primary base station:
 Controls the access of primary users to spectrum
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Secondary network
◦ Secondary users:
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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.
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CR Network Access:
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CR Ad Hoc Access:
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Primary Network Access : CRs can access primary
CRs can access their own base
station on both licensed and unlicensed spectrum bands
CRs can communicate with other
CRs through an ad hoc connection on both licensed and
unlicensed spectrum bands.
base station through the licensed bands.
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Spectrum sensing: Cognitive radio user has the ability to
sense the unused spectrum at any time and location.
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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
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Requires a cross layer design
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Physical layer:
◦ spectrum sensing
◦ data reconfigurable transmission based on Software
Defined Radio (SDR).
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Link Layer :
◦ spectrum analysis
◦ spectrum selection(spectrum adjustment)
◦ spectrum coordination.
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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).
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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
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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).
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The first IEEE standard utilizing cognitive radio (CR)
technology to exploit the television white space.
The focus was on building fixed point-tomultipoint WRAN that utilizes UHF/VHF TV bands
between 54 and 862 MHz.
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Leased network
Cognitive mesh network
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Emergency network
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Military network
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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
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Transmitter-receiver handshake: After deciding a
portion of the spectrum, the receiver of this communication
should also be indicated.
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Spectrum mobility: If the specific portion of the spectrum
is needed by a licensed user, the communication needs be
continued in another vacant portion.
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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.
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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
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Spectrum access technique:
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Overlay spectrum sharing: Portion of the spectrum can be accessed
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Underlay spectrum sharing: Transmission of a CR node is regarded as
that has not been used by licensed users.
noise by licensed users.
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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.
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Game theoretical overview of dynamic spectrum sharing
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The behavior of the cognitive radios in
dynamic spectrum access networks can be
modeled as a dynamic spectrum sharing
game (DSSG).
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Non-cooperative DSSG without centralized
control
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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 noncooperative game with incomplete information. Auction
theory is applied to formulate and analyze the
interactions.
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Local Bargaining
◦ The product of user throughput is considered the
optimization goal of local bargaining
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Repeated Spectrum Sharing Game Model
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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.
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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
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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.
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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
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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
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[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 CommunicationAware 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.”