Cooperative Sensing in One Cell — In the one-cell case, CR
devices sense channels at the same time. Synchronization
among cooperative CR devices is usually achieved in an
infrastructure-based architecture. For instance, in a CR-based
picocell network, the CR picocell BS manages the network
and serves as a fusion center. Upon receiving a request for
spectrum sensing, the BS will send out a scheduling instruction
to the cooperative CR devices. The cooperative CR
devices could cooperatively sense the licensed spectrum in the
picocell. After cooperative sensing, the participating devices
send the sensing result to the CR picocell BS for a final decision.