  Cognitive radio is an intelligent radio that can be programmed and configured
dynamically to fully use the frequency resources that are not used by licensed
users. It defines the radio devices that are capable of learning and adapting
to their transmission to the external radio environment, which means it has
some kind of intelligence for monitoring the radio environment, learning the
environment and make smart decisions. In this paper, we are reviewing some
examples of the usage of machine learning techniques in cognitive radio
networks for implementing the intelligent radio.
