  Nowadays, cognitive radio is one of the most promising paradigms in the arena
of wireless communications, as it aims at the proficient use of radio
resources. Proper utilization of the radio spectrum requires dynamic spectrum
accessing. To this end, spectrum sensing is undoubtedly necessary. In this
chapter, various approaches for dynamic spectrum access scheme are presented,
together with a survey of spectrum sensing methodologies for cognitive radio.
Moreover, the challenges are analyzed that are associated with spectrum sensing
and dynamic spectrum access techniques. Sensing beacon transmitted from
different cognitive terminals creates significant interference to the primary
users if proper precautions have not be not taken into consideration.
Consequently, cognitive radio transmitter power control will be finally
addressed to analyze energy efficiency aspects.
