In this thesis work we have proposed an Adaptive Power Transmission scheme for Cognitive Radio. The proposed scheme estimates the distance between the primary user and the Cognitive Radio, using the SNR as proxy for distance, also utilizing the information of IT (Interference Temperature). On the basis of these information the Cognitive radio adaptively changes its transmit power to prevent the primary user from harmful interference. The most challenging problem of cognitive radio is the interference which occurs when a cognitive radio accesses a licensed band but fails to notice the presence of the licensed user. Another challenge is to compute the correct distance between the cognitive radio and the primary user. To allow the cognitive radio to access the same spectrum band where the primary user is operating creates a problem, in such case; the cognitive radio may interfere with the primary system, hence degrading the quality of service for the primary receiver. The Primary goal of this work is to propose Adaptive power control based on the estimated distance between the cognitive radio and primary user. We will discuss the transmit power being controlled on the basis of distance. But there is no such method to calculate the exact distance between the cognitive radio and the primary user, so that we interpret distance in terms of SNR. We will propose a method to make the CR so intelligent that it can determine the maximum level of the transmission power which does not cause any harmful interference to the primer user’s quality of service.