The primary functions of cognitive radio include power control, spectrum sensing using various techniques like transmitter detection, matched filter detection, energy detection, and cyclostationary feature detection. It also includes spectrum management, wideband spectrum sensing, and cooperative detection. Spectrum sensing techniques can be categorized into transmitter detection using methods like matched filtering and energy detection. Energy detection measures signal power to detect presence/absence but requires knowledge of noise variance while cyclostationary feature detection exploits unique features of communication signals. Wideband sensing and cooperative detection are also discussed.