A New Technique for Capacity Enhancement in WCDMA Uplink with Synchronization

Abstract

Cellular phones have experienced an exponential growth worldwide over the last decade with more than one billion cell phone users projected in the near future. On the other hand, service providers must support new technology and infrastructure in order to fulfill their customers' requirements. These requirements include the capacity of network. The large expectances created for Wide Band Code Division Multiple Access (WCDMA) are based on its flexibility for multimedia capabilities and the high capacity it will provide. However, the demanded traffic grows rapidly, and new capacity enhancements are required in order to satisfy the future needs. Uplink synchronization can be a method to reduce the multiple access interference (MAI) by exploiting the uplink orthogonality and thereby increase the capacity of WCDMA systems. In this paper, the performance of uplink synchronous WCDMA has been assessed in terms of the capacity gain relative to an equivalent asynchronous system. The capacity gain has been evaluated theoretically and by means of MATLAB simulations for scenarios with different orthogonality factors. Orthogonality of codes is directly dependent on synchronization which in turn increases the capacity gain. In this study, it is proposed that synchronization plays an important role in enhancing the capacity gain of uplink WCDMA system. Also, an alternative solution is proposed to increase the capacity in the uplink of a synchronized WCDMA system by introducing variable modulation.