Date Added: Oct 2011
As a limited nature resource, wireless spectrum becomes increasingly scarce. However, it is not utilized efficiently; the current utilization of a licensed spectrum varies from 15% to 85%. And the number is even lower in rural area. Cognitive Radio (CR) is a key technology to mitigate the overcrowding of spectrum space based on its capability of Dynamic Spectrum Access (DSA). A CR system is an intelligent wireless communication system that is aware of its surrounding environment, learns from the environment, and adapts its operating parameters in real time. One fundamental requirement of CR system is to find the frequency hole by Secondary User (SU).