Cognitive radios (CRs) have been proposed as a possible solution to improve spectrum utilization by enabling
opportunistic spectrum sharing. The main requirement for allowing CRs to use licensed spectrum on a secondary
basis is not causing interference to primary users. Spectrum sensing allows cognitive users to autonomously identify
unused portions of the radio spectrum, and thus avoid interference to primary users. In this work, energy detection
technique is considered for spectrum sensing, and the performance evaluation of an energy detector is presented. The
process of threshold selection for energy detection is addressed by the Constant False Alarm Rate (CFAR) method
and selection is carried out considering present conditions of noise levels. Our results show that if we dynamically
adjust detection-threshold based to the noise level present during detection process, the detection probability will be
higher than the one obtained when a fixed threshold value is considered