Since the onset of the explosive growth in demand for wireless communications during the 1990s, researchers are giving increasing attention to the use of adaptive antenna systems (AASs) technology to overcome practical challenges in providing the service. The main benefit of the technology lies in its ability to exploit the spatial domain, on top of the temporal and frequency domains, to improve on transceiver performance. This thesis presents a unified study on two classes of preprocessing techniques for uniform circular arrays (UCAs). UCAs are of interest because of their natural ability to provide a full azimuth coverage found in typical wireless communication scenarios. The two classes of preprocessing techniques studied are the Davies transformation and the interpolated array transformations. These techniques yield a mathematically more convenient form of the array steering vector for different algorithms in correlated signal environment. In addition to the algorithm level studies, the thesis also investigates the use of AAS technology with respect to two different 3G mobile communications systems: Enhanced Data rates for Global Evolution (EDGE) and Wideband Code Division Multiple Access (WCDMA).