Performance Evaluation of Cellular DS-CDMA Systems

Abstract

Cellular radio can be regarded as the earliest form of wireless “personal communication”. It allows the subscriber to place and receive telephone calls wherever cellular coverage is provided. But with the pessage of time, it becomes more and more difficult to accomodate a large number of users within a limited frequency band. This thesis addresses capacity estimation and a review of work carried out by various authors for Direct Sequence Code Division Multiple Access (DSCDMA) cellular mobile systems. Capacity is defined as total number of simultaneous users in a cell that can be served by the system with the predefined performance in a geographical area. An analytical approach has been used to estimate the capacity in worst conditions and IS-95 standard is being used as a reference. The interference contributions are studied on the fixed number of user’s in a log-normally shadowing channel. Outage probability is taken as the main criteria for the esimation of capacity. Capacity results for up-link in different shadowing and channel conditions are discussed for a given outage probability. Effect of capacity enhancement features like power control, antenna beam sectorization and voice activity factor are also discussed. A comparison against previously published CDMA capacity estimates is carried out, aimed at classifying some controversial issues. It is also confirmed that large system capacity is achievable under tight power control.