The CR network should be aware of the surrounding radio environment and regulate its transmission accordingly.
In interference-free CR networks, CR users are allowed to borrow spectrum resources only when licensed users do not use them.
A key to enabling interference free CR networks is figuring out how to detect the spectrum holes (white space) that spread out in wideband frequency spectrums.
CR receivers should first monitor and allocate the unused spectrums via spectrum sensing (or combining with geolocation databases) and feed this information back to the CR transmitter.