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What is Cognitive Radio Network?

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Cognitive radio 

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.

Spectrum  hole

Network  access types:

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.

Functionalities  of a CRN:

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.


Spectrum  sharing

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



Classifications  of spectrum sharing:

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.

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