Providing communication to anybody, anywhere, anytime is the goal of the third generation communication wireless systems and one of the challenges in achieving these goals is to cope with increasing levels of interference that result from dramatically increased number of user. CDMA (Code Division Multiple Access) as a multiple-access technique offers a better counter tools to overcome the challenges and fulfils the demands of third-generation mobile users. CDMA is characterized by low probability of interception, robust to interference and jamming rejection, high time resolution, and immunity to multipath effects. However, these advantages cost relatively more processing. The capacity of CDMA based mobile cellular system is interference limited. Moreover, the path loss exponent plays a key role in the overall performance of the system. In this paper, we have analyzed the effects of interferences on DS-CDMA (Direct Sequence Code Division Multiple Access) cellular system imposed by the variations in the number of users and processing gain as well as with the addition of layers considering different path loss exponents. The two cases are considered separately.