Cognitive Radio Networks (CRN) are radio systems designed to improve the throughput of radio networks. They are flexible, adaptable radio networks with cognitive and reconfigurable properties.
CRN networks can discover unoccupied radio frequencies and use them for their own transmission purposes, thus making better use of the radio frequency spectrum. The network nodes of CRN networks are formed by intelligent cognitive radios(CRs).
The cognitive procedure used in CRN networks is first about observing and sensing. Through these functions, the radios locate each other and activate the CRN network. The next step is to detect and analyze the frequency spectrum. To do this, all radios measure the frequency spectrum and determine where available radio frequencies are located. And the final step is about accessing the network and transmitting. Since each radio has a different relationship to the radio frequencies, whether due to shadowing, long distance, or different field strengths of the radio signals, the cognitive radios, which are the cognitive users( CU), must communicate with each other using a common protocol. This choice depends very much on the CRN infrastructure.