Spatial filtering for pilot-aided WCDMA systems: a semi-blind subspace approach

This paper proposes a spatial filtering technique for the reception of pilot-aided multirate multicode direct-sequence code division multiple access (DS/CDMA) systems such as wideband CDMA (WCDMA). These systems introduce a code-multiplexed pilot sequence that can be used for the estimation of the filter weights, but the presence of the traffic signal (transmitted at the same time as the pilot sequence) corrupts that estimation and degrades the performance of the filter significantly. This is caused by the fact that although the traffic and pilot signals are usually designed to be orthogonal, the frequency selectivity of the channel degrades this orthogonality at hte receiving end. Here, we propose a semi-blind technique that eliminates the self-noise caused by the code-multiplexing of the pilot. We derive analytically the asymptotic performance of both the training-only and the semi-blind techniques and compare them with the actual simulated performance. It is shown, both analytically and via simulation, that high gains can be achieved with respect to training-onlybased techniques.Peer Reviewe

Space time transceiver design over multipath fading channels

Imperial Users onl

Enhancement of Space-Time Receiver Structure with Multiuser Detection for Wideband CDMA Communication Systems

Wideband CDMA (WCDMA) which has been accepted as one of the radio access technology for third generation (3G) systems has many advantages such as efficient spectrum utilization and variable user data rates. However, multiple access interference (MAI) is a major constraint limiting the capacity of the system. Multiuser detection and smart antenna technologies are capable of increasing the system capacity through mitigation of such impairment. In this thesis, a combination of spatial signal processing with temporal signal processing is proposed. Additionally, the space-time receiver structure is combined with multiuser detection to further enhance the system. We propose and analyze different combined space-time linear multiuser detection configurations in an uplink mobile radio communications channel that incorporates the spatial temporal parameters. The performance of these receivers is evaluated as a function of the number of antenna elements, Rake fingers and number of users. We consider two different pilot symbol assisted adaptive beamforming algorithms, Least Mean Square (LMS) and Recursive Least Square (RLS). The algorithms are used to adjust the weights of the antenna array to form the appropriate beam patterns to track the desired user and null interfering users. The adaptive algorithms are evaluated as a function of the number of iterations it takes to converge and its transmission performance are compared. Additionally, two different linear multiuser detection techniques, Decorrelator and linear Minimum Mean Square Error (MMSE) strategies are used in conjunction with the combined receiver structure.The proposed combined Space Time Multiuser Detector which is suitable for WCDMA systems is shown to provide significant gain in transmission performance and system capacity. It is shown via simulation that the combined RLS adaptive algorithm with the linear MMSE multiuser detector provides the best overall performance. The simulation result also shows that the combined receiver structure is robust in the presence of strong interference due to high data rate users