Cognitive radio (cr) is a promising technology for next-generation wireless networks in order to efficiently utilize the limited spectrum resources and satisfy the rapidly increasing demand for wireless applications and services. in cognitive radio technology, the wireless system is used to find a vacant band that cognitive radio user can use when its use doesn’t interrupts the primary user. during the mobility of secondary user has to move from one primary user system to another primary user system. so the user should check periodically whether the band is still vacant for channel selection and the optimal time interval between two successive checks for spectrum availability, we are using spectrum sensing and geo-location database scheme. we have to maximize the duration of spectrum availability checks while ensuring that the probability of the cognitive radio user disturbs the primary user (pu) should less than a specified threshold. authenticating the pu signal in order to mitigate pu emulation attacks. authenticating primary user’s signal in crn integrates link signatures and cryptographic mechanisms.