TODAY’S wireless networks are characterized by a static

spectrum assignment policy. Recently, due to the increase

in spectrum demand, however, this policy is faced with

the spectrum scarcity at particular spectrum bands. On the

contrary, a large portion of the assigned spectrum is still

used sporadically leading to under-utilization of the significant

amount of spectrum [1]. The limited available spectrum

and the inefficiency in spectrum usage make it necessary to

develop a new communication paradigm to exploit the existing

wireless spectrum opportunistically. Cognitive radio technology

is proposed to solve these current spectrum inefficiency

problems