1. Cognitive Radio Networks
Under the guidance of: Mr G. Praveen Babu Associate Professor
Presented By: Nata Raju G 11031D6427 M.Tech – CNIS

2. 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

3. 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).

5. 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
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.

8. 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.

9. Fig 2: Spectrum hole concept
Temporarily unused licensed spectrum
Fig 2: Spectrum hole concept

10. 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.

11. 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

13. 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

15. Spectrum management
Functions incorporated in CRAHNs for adapting to the dynamic spectrum environment:
Spectrum sensing
Spectrum decision
Spectrum sharing
Spectrum mobility

16. …continue 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

17. …continue 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

18. …continue 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.

19. …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.

20. 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.

21. …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.

22. Cognitive cycle
Spectrum management functions necessary for adapting to dynamic spectrum environment from a cognitive cycle as shown below:
Fig. 6 Cognitive cycle

23. References
[1] “Cognitive Radio Ad Hoc Networks” 7 (2009) , 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): [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):

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