One of the fundamental problems for the future wireless systems is where to find suitable spectrum bands to meet the demand of future services. While essentially all of the radio spectrum is allocated to different services, applications and users, observation provide evidence that usage of the spectrum is actually quite low. In order to overcome this problem and improve spectrum utilization, cognitive radio concept has been proposed an application with this radio is spectrum sensing which is biggest issue that can detect the spectrum holes or detects the presence of primary users. Cognitive radios works on dynamic spectrum access where any spectrum hole detected by spectrum sensing is then allocated to the secondary user without interfering the primary users. This paper gives an overview of some spectrum sensing techniques and dynamic spectrum access methods.

Keywords : Cognitive radio, spectrum sensing, dynamic spectrum access.