It has been widely recognized that the valuable, yet finite radio spectrum is being underutilized by licensed systems both spatially and temporally. To realize a more efficient use of this valuable resource, secondary spectrum usage by cognitive radios is being considered. Cognitive Radio is a paradigm for wireless communication in which either a network or a wireless node changes its transmission or reception parameters to communicate effectively while avoiding interference to licensed users. The cognitive radio in its operation may want to make opportunistic use of spectrum that is already allocated to primary users and adjust itself to certain conditions so that it does not impair the operation of these primary users. The purpose of this thesis is to investigate the feasibility of deploying cognitive radios within a Licensed User (LU) network without causing harmful interference. This thesis shows that this may be possible provided certain conditions are met by the cognitive radios thereby achieving a more efficient use of the scarce frequency spectrum. The approach for this work is to model and analyze an interference scenario involving a cognitive radio interferer (secondary user) and a victim licensed receiver (primary user). The case scenario being considered involves secondary users which are being represented by public safety organizations (police, fire brigade and ambulance) who normally use the 380-400MHz band for Emergency communications (in Europe). The primary users are considered to be commercial Private Mobile Radio systems operating in the 450-470MHz band. Secondary access to the latter band could help to offload the 380-400 MHz band in crisis situations.