ABSTRACT
In recent years, a rapid increase of wireless devices and services has led to a dramatic increase in the demand for radio spectrum. But radio spectrum suitable for wireless communications is very limited. Thus, spectrum scarcity is becoming more and more serious. In parallel with that, many spectrum bands are extremely underutilized under traditional fixed spectrum assignment policy, as reported by the Federal Communications Commission (FCC) in [1]. Cognitive radio (CR) is then proposed as a promising technique to fully utilize the spectrum resource. CR technique enables unlicensed users or secondary users (SUs) to exploit the unutilized spectrum bands assigned to licensed users or primary users (PUs) without harmfully interfering PUs’ services [2].
