To fully exploit wireless radio resource and, thus,

increase spectrum efficiency, cognitive radios shall sense wire-

less environments and identify interference to allow opportunis-

tic transmissions for secondary systems. Based on Chen et al.

in their work about a terminal architecture for cognitive radio

networks, by further obtaining transmission information with a

rate–distance nature that is extended an overlay concept,

secondary systems can even leverage busy duration of primary

systems to enhance the opportunity to use spectrum under de-

rived tolerable interference to the primary orthogonal frequency-

division multiple access (OFDMA) system.-To fully exploit wireless radio resource and, thus,

increase spectrum efficiency, cognitive radios shall sense wire-

less environments and identify interference to allow opportunis-

tic transmissions for secondary systems. Based on Chen et al.

in their work about a terminal architecture for cognitive radio

networks, by further obtaining transmission information with a

rate–distance nature that is extended　an overlay concept,

secondary systems can even leverage busy duration of primary

systems to enhance the opportunity to use spectrum under de-

rived tolerable interference to the primary orthogonal frequency-

division multiple access (OFDMA) system.