Cognitive radio is different from the traditional radio
that it owns the ability of cognitive intelligence and realizes
the real-time detection of environment. Through
adaptive change parameter settings for the study and decision-
making, it can make full use of spectrum resources
effective. The prerequisite for CR is the openness of the
spectrum, that is, the network should be divided into
Primary users (authorized users) and subprime users (unauthorized
users). On the basis of the spectrum openness,
subprime users can find out the idle spectrum by detecting
spectrum hole which the Primary users don’t use
right now, and make full use to access frequency band
without impact on the premise of the user communication
[2]. This requires subprime users with the ability of
the real-time detection for spectrum hole, having the following
three characteristics [3]: