Cognitive Radio System is a form of wireless communication in which a transceiver detects the communication channels which are in use and which are not in use.

The Cognitive Radio Network (CRN) is broadly classified into two major networks, a primary network and a secondary network. Cognitive Radio users are unlicensed users and they used to find unused licensed spectrum for their own use without causing any interference to licensed users.


1 – Spectrum Sensing

CR devices can closely track all the spectrum bands located in the nearby surroundings to identify the primary users and spectrum holes.

Figure 1: Spectrum Sensing Techniques.

• Primary users are the users who are licensed and allowed to operate only in a particular spectrum band.

• Spectrum holes are the spaces which is available in a spectrum band that may be availed by unlicensed users. Spectrum holes are created and removed in real-time.

2 – Spectrum Database

Federal Communications Commission (FCC) proposed a spectrum database concept which insisted to remove the complexity of spectrum sensing technique and to use TV white space as an alternative. All the TV stations were asked to update their next week usage in the database which was maintained by FCC. CR devices can look up for free spectrum information from this database. CR devices will have knowledge about free spectrum for use and can violate the need for complex sensing which requires time and money.

Fig 2 : radio frequency spectrum bands.


1. Cognition: CR can understand its geographical and operational environment.

2. Reconfiguration: According to cognitive knowledge, CR could autonomously adjust its parameters.

3. Learning: CR can grasp from the experience and experiment with new configurations in new situations accordingly.


Heterogeneous CR: The operators run several radio access networks (RANs) by using different radio access technology (RAT) protocols. This type of radio will use a network – centric approach.

Spectrum – sharing CR: In this type, several RANs share the same frequency band. They also synchronize with each other to use unoccupied sub-bands effectively.


• City and campus wide network RF coverage.

• Leased networks.

• Disaster rescue works.

• Emergency networks.

• Cognitive mesh networks.

• Medicinal applications.

• Weather forecasting.

• Traffic control System.