Cognitive radio is a novel concept that enables wireless systems to sense the environment,
adapt, and learn from previous experience to improve the quality of the communication.
However, CR requires a flexible and adaptive physical layer in order to perform the required
tasks efficiently. In this article, CR systems and their requirement of a physical layer are
discussed, and the orthogonal frequency division multiplexing technique is investigated as a
candidate transmission technology for CR. The challenges that arise from employing OFDM …

With emerging technologies and with the ever increasing number of wireless devices, the
radio spectrum is becoming scarcer everyday. On the other hand, measurements show that
wide ranges of the spectrum are rarely used most of the time while other bands are heavily
used. However, those unused portions of the spectrum are licensed and thus cannot be
utilized by users other than the license owners. Hence, there is a need for a novel
technology that can benefit from these opportunities. Cognitive radio arises to be a tempting …