Transcript cognitive radio networks ppt nata raju g - 11031d6427

Cognitive Radio
Networks
Under the guidance of:
Mr G.Praveen Babu
Associate Professor
Presented By:
Nata Raju G (11031D6427)
M.Tech – CNIS
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Outline
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Today's wireless systems
Cognitive radio (CR) system
Characteristics of cognitive radio system
Spectrum hole concept
Wireless ad hoc networks
Classification of Cognitive radio networks
Cognitive radio ad hoc networks (CRAHNs)
architecture
• Spectrum management in CRAHNs
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Today’s Wireless System
• Most of the spectrums (licensed bands) are already
allocated for license users for exclusive use.
• Few, Small, unlicensed bands are left open for
unlicensed users (ISM bands 900MHz and 2.4 GHz)
• Technological advancement has resulted in the huge
development of personal wireless technologies like Wi-Fi/802.11, Bluetooth, digital cordless phones, 3G,
and so on which operate on unlicensed band.
• Licensed bands are under-utilized but unlicensed bands
are crowded resulting on spectrum scarcity.
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• Solution is to let unlicensed users use the
licensed frequencies, provided they can
guarantee interference perceived by the
primary license holders will be minimal (a
concept of cognitive radio).
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Cognitive Radio(CR) System
• Allows the unlicensed users to dynamically
and opportunistically access the “underutilized" licensed bands
• Cognitive Radio
- Termed by Joseph Mitola in 1991
- “Radio that includes a transmitter in which
operating parameters such as frequency
range, modulation type or maximum
output power can be altered by software."
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- A software-defined radio with some artificial
intelligence to make detection and wise decision
according to its environment
Fig 1: An example of cognitive radio system components
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• In order to access “under-utilized” licensed bands
dynamically and opportunistically, Cognitive Radio has
to
- identify the spectrum opportunities (idle frequency
bands) in spatial and frequency domain.
- or use the licensed spectrum with transmit
power constraint so that the interference
created by secondary users is below the
tolerable limit.
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Characteristics of Cognitive Radio
System
• Cognitive capability
– Ability to capture or sense the information from
its radio environment and allows to identify and
select the portion of the spectrum that are
unused at a specific time or location.
• Reconfigurability
– Dynamically programmable capability according
to radio environment to transmit and receive on a
variety of frequencies.
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Spectrum hole concept
• Spectrum hole
– Temporarily unused licensed spectrum
Fig 2: Spectrum hole concept
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Wireless ad hoc networks
• Ad hoc means
- "for this," further meaning “ for this
situation on hand.”
• Wireless ad hoc network
-It is a self-organizing and self-configuring
infrastructure less network connected by wireless
links, in which most of the network
devices are part of the network only for the
duration of a communications session.
• Most of the wireless devices available today
communicate through wireless ad hoc networks.
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Classification of CR networks
• Infrastructure based CR networks
– Has a central network entity to coordinate
communication such as base station in cellular
networks and access point in wireless LANs.
Fig 3: An example of infrastructure based CR networks
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• Cognitive radio ad hoc networks(CRAHNs)
– Infrastructure less network
– Does not have a central network entity
– A CR user can communicate with other CR users through
ad hoc connection on both licensed and unlicensed
spectrum bands.
Fig 4: An example of CRAHNs
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CRAHN Architecture
• Consists of two groups
– Primary networks
• Existing network, where the primary users (PUs) have a
license to operate in a certain spectrum band.
• Operations of PUs are controlled through primary base
stations.
– Cognitive radio networks
• Does not have license to operate in a desired band.
• Additional functionality is incorporated to share the
licensed spectrum band.
• Cognitive radio (CR) users are mobile and can
communicate in a multi-hop manner on both licensed
and unlicensed spectrum bands.
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Fig. 5 : CRAHN Architecture
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Spectrum management
• Functions incorporated in CRAHNs for
adapting to the dynamic spectrum
environment:
– Spectrum sensing
– Spectrum decision
– Spectrum sharing
– Spectrum mobility
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• Spectrum sensing
– A function in CR networks to monitor the unused spectrum bands.
– Provides the spectrum availability information required for other
functions.
– It is achieved thorough:
• PU detection
CR user observes and analyzes its local radio environment
and determines the presence of PU transmissions and
accordingly identifies the current spectrum availability if
exists.
• Cooperation
Observed information by CR user is exchanged with its
neighbors to improve sensing accuracy
• Sensing control
Coordinates the sensing operations of the CR users and its
neighbors
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• Spectrum Decision
– A function to select the most appropriate band (after
spectrum sensing) according to the quality of service (QoS)
requirement.
– Spectrum selection decision is performed considering endto-end route consisting of multiple hops.
– Available spectrum bands in CR network may differ from
one hop to the other.
– It is achieved through:
• Spectrum characterization
CR user observes the characteristics of each available spectrum
which may be varying over time and space due to PU activities
• Spectrum Selection
CR user finds the best spectrum for each hope to satisfy the QoS
requirement for end-to-end route
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• Spectrum Sharing
– Enables CR users to perform channel selection and
power allocation according to their QoS
– It is achieved through:
• Resource allocation
Based on QoS, CR users selects the proper channel and adjust
their transmission power.
• Spectrum access
Enables multiple CR users to share the channel determining
who will access the channel or when a user may access a
channel.
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…continue spectrum sharing
• Medium access protocols for spectrum access
– Random access
• Channel may be opportunistically captured by any CR user for
control and data exchanges
– Time slotted
• Control and data are assigned fixed durations and prevent
simultaneous transmission by multiple users
– Hybrid
• Fixed time duration for control packets followed by random access
for capturing the channel before data transfer.
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• Spectrum mobility
– CR users are mobile and so called visitors to the
spectrum
– If the spectrum in use by a CR user is required for
PU, the communication of the CR user needs to be
continued in another vacant portion of the
spectrum.
– Spectrum mobility is required when:
• PU is detected
• CR user loses its connection due to mobility of other
users
• Current spectrum band cannot provide the QoS
requirements.
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…continue spectrum mobility
• Spectrum mobility is achieved through
– Spectrum handoff
• CR user switches the spectrum band physically and
reconfigures the communication parameters (e.g.
operating frequency, modulation type)
– Connection management
• CR user sustains the QoS or minimizes quality
degradation during spectrum switching by interacting
with each layer.
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Cognitive cycle
• Spectrum management functions necessary
for adapting to dynamic spectrum
environment from a cognitive cycle as shown
below:
Fig. 6 Cognitive cycle
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References
[1] “Cognitive Radio Ad Hoc Networks” 7 (2009) 810-836,
Ian F. Akyildiz , Won-Lee, Kaushik R. Chowdhury
[2] Akyildiz, I.F.; Won-Yeol Lee; Vuran, M.C.; Mohanty, S.
“A Survey on Spectrum Management in Cognitive Radio
Networks” communications magazine, IEEE, vol. 46,
Publication Year: 2008 , Page(s): 40 - 48
[3] Akyildiz, I.; Won-Yeol Lee; Chowdhury, K. , “Spectrum
Management in Cognitive Radio Ad Hoc Networks”
Network ,IEEE, Volume: 23, Publication Year: 2009 ,
Page(s): 6 - 12
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