Some Investigations on Multiuser detection for CDMA systems

Abstract

Over the last few years, wireless cellular communications has experienced rapid growth in the demand for provision of high data rate wireless multimedia services. This fact motivates the need to find ways to improve the spectrum efficiency of wireless communication systems. However, in order to achieve this promised high capacity, good techniques are needed to overcome several wireless impairments such as fading and multiuser interference. This is why significant research work is currently being devoted to improve the performance of Direct Sequence Code Division Multiple Access (DS-CDMA) systems using different techniques, such as interference cancellation or multiuser detection (MUD), smart antenna and power control. Among these areas of research, multiuser detection is one of the most crucial aspects because it plays an important role in DS-CDMA systems. The aim of this study is to contribute to this important research area by studying existing multiuser detection algorithms, suggesting ways to use these methods practically at reduced complexity. Code Division Multiple Access (CDMA) is chosen as the platform for this thesis work since it has been adopted as the air-interface technology by the Third Generation (3G) wireless communication systems. Also, smart or adaptive antennas have also emerged as a promising technology to enhance the spectrum efficiency of present and future wireless communications systems by exploiting the spatial domain. Further, all future generation systems are required to support multiple data rates with good quality of service. These aspects are studied.