Cognitive Radio Networks

Presented By:Nata Raju G (11031D6427)

M.Tech – CNIS

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Under the guidance of:Mr G.Praveen Babu

Associate Professor

Outline• 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 “under-utilized" 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

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Fig 1: An example of cognitive radio system components

…continue• 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

9Fig 2: Spectrum hole concept

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.10

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.

11Fig 3: An example of infrastructure based CR networks

…continue classification

• 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.

12Fig 4: An example of CRAHNs

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

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 detectionCR 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 controlCoordinates 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 end-to-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 accessEnables 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:

22Fig. 6 Cognitive cycle

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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