Limits on Secondary Transmissions Operating in Uplink Frequencies in Cellular CDMA Networks

It is well known that electromagnetic radio spectrum is very expensive. This spectrum is managed by government agencies which divides it into frequency bands and then allocates bands to different types of services such as TV broadcasting, cellular telephony ,military usage etc. Lately, the increasing number of wireless technologies and rapid increase in the number of users in cellular telephony highlighted the emerging shortage in the allocated spectrum. From measurements, it has been shown that a major cause of this shortage is inefficient use of spectrum. Many services are active, but they do not have a 100% duty cycle, thus systems are often not operating at full capacity much of the time, which creates a gap in spectrum usage. Thus, the idea of secondary user transmissions has been developed. A secondary user is a non-licensed user which uses licensed spectrum when it is unoccupied by the primary user (i.e., the license holder). These secondary transmissions can happen only as long as the interference caused by them does not harm the primary users by decreasing their quality of service (QoS) or in the worst case scenario by denying them access.\ud The focus of this dissertation is on better usage of the uplink frequency bands of cellular CDMA networks. We calculate the number of secondary transmissions possible in the cell radius whenever the cell is not operating at full capacity. Further, we explore the possibilities and limitations that such secondary users face in that cell, always keeping in mind the interference that will be caused to primary transmissions (at the Base transceiver subsystem-BTS) must be less than the threshold that is required to maintain adequate quality of service. We employ simple analysis and we have performed simulations to calculate the dependence of the number of secondary users based on the number of active primary users and also to calculate the interference on the secondary users to evaluate the possibilities and potential for secondary user applications.\u