Cognitive radio is where wireless devices are sufficiently computationally intelligent about radio resources and related computer-to-computer communications to detect user communications needs as a function of use context, and provide radio resources and wireless services most appropriate to those needs. Its roots came from the discovery by regulatory bodies in various countries which found that most of the radio frequency spectrum was inefficiently utilised. For example, cellular network bands are overloaded in most parts of the world, but amateur radio and paging frequencies are not. Independent studies concluded that spectrum utilization depends strongly on time and place. Moreover, fixed spectrum allocation prevents rarely used frequencies from being used by unlicensed users, even when their transmissions would not interfere at all with the assigned service. This was the reason for allowing unlicensed users to utilize licensed bands whenever it would not cause any interference.

Cognitive radio c an monitor, observe, and react to events in a specified environment. The fundamental benefits are the ability to self-adapt, self-manage, and self-optimize under normal conditions, and the ability to self-diagnose and self-heal when unusual problems arise e.g. base stations can automatically adjust operating range (e.g., by controlling transmit power, receiver sensitivity, data rate, frequency channel selection) to compensate for neighboring base stations that fail. In contrast to many wireless systems where static frequency channels are pre-selected in advance and tedious frequency planning is mandatory to minimize interference from equipment operating in adjacent coverage areas. CR can achieve a performance that is close to a licensed band even when using an unlicensed band due primarily to its inherent ability to switch to best channels . This paper provides an overview of Cognitive Radio.