Cognitive radio has emerged as a promising technology for maximizing the utiliza-
tion of the limited radio bandwidth while accommodating the increasing amount of
services and applications in wireless networks. A cognitive radio (CR) transceiver
is able to adapt to the dynamic radio environment and the network parameters to
maximize the utilization of the limited radio resources while providing flexibility in
wireless access. The key features of a CR transceiver are awareness of the radio envi-
ronment (in terms of spectrum usage, power spectral density of transmitted/received
signals, wireless protocol signaling) and intelligence.
