Cognitive radio (CR) has attracted significant attention due to expected radio frequency (RF) spectrum scarcity with ever-increasing demands. CR networks, which strive to utilize opportunistically the RF spectrum, require new ways of looking at interference in wireless networks. Since a decrease in transmit power translates into an increase in energy efficiency and a decrease in RF interference, communication ranges have been shrinking dramatically in recently emerging wireless technologies. Prominent examples of decrease-in-transmit-power strategies are CR relays in CR networks and femtocells in next generation wireless networks (NGWNs). Therefore, the impact of mobility especially with respect to relatively small displacements needs to be investigated. In this study, a comprehensive interference model is considered and examined by taking into account all of the basic propagation mechanisms such as large- and small-scale fading under a generic single secondary user (SU) and single primary user (PU) scenario. The analysis and corresponding numerical results are given and discussed.