Introduction - If you have any usage issues, please Google them yourself
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.