Investigations into Smart Antennas for CDMA Wireless Systems

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. Smart or adaptive antennas have emerged as a promising technology to enhance the spectrum efficiency of present and future wireless communications systems by exploiting the spatial domain. The aim of this thesis is to investigate smart antenna applications for Direct Sequence Code Division Multiple Access (DS-CDMA) systems. 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. The main role of smart antennas is to mitigate Multiple Access Interference (MAI) by beamforming (i.e. spatial filtering) operation. Therefore, irrespective of a particular wireless communication system, it is important to consider whether a chosen array configuration will enable optimal performance. In this thesis an initial assessment is carried out considering linear and circular array of dipoles, that can be part of a base station antenna system. A unified and systematic approach is proposed to analyse and compare the interference rejection capabilities of the two array configurations in terms of the Signal to Interference Ratio (SIR) at the array output. The theoretical framework is then extended to include the effect of mutual coupling, which is modelled using both analytical and simulation methods. Results show that when the performance is averaged over all angles of arrival and mutual coupling is negligible, linear arrays show similar performance as circular arrays. Thus in the remaining part of this thesis, only linear arrays are considered. In order to properly evaluate the performance of smart antenna systems, a realistic channel model is required that takes into account both temporal and spatial propagation char-