الفهرس | Only 14 pages are availabe for public view |
Abstract This thesis treats some modeling and estimation problems in the field of antenna array signal processing. With multiple antennas at the receive side, the spatial dimension is added, and processing is performed in both the temporal and spatial domain. The work is motivated by the interest in using antenna arrays, primarily at the base stations, in wireless communication systems. Among the potential benefits are increased range, fading diversity, interference rejection and spatially selective transmission. The thesis is divided into two parts: spatial and spatial-temporal processing parts. The first part focuses on the problem of estimating the channel parameters i.e. Direction Of Arrival (DOA) referred as spatial signatures for a uniform linear array. Different algorithms for estimating the DOAs of the signals received at the array are provided and investigated. Both of narrowband and wideband signals either uncorrelated or coherent are considered. Performance comparisons between these DOA algorithms for different signal types are performed. It was shown that when the spatial-only models are used to deal with the coherent signals as in multipath environments, most of DOA methods may probably fail. This is because the signal models are assumed to be narrowband with inverse bandwidth small in comparison to the time dispersion introduced by the propagation as well as the channels are modeled as non-frequency selective with small angular spread . AJso, the DOA estimation in different propagation environments such open, urban, suburban, and urban areas are studied. It is proved that the DOA estimation accuracy depends on environment type. The simulation shows that better DOA estimations can be obtained in simple propagation environments such as open and suburban areas while lesser accuracy is achieved in complicated one such as urban areas. This is because the Signal to Noise Ratios (SNRs) obtained in complicated propagation areas are lower than that obtained in simple propagation one. Some improvements can be performed by increasing the antenna gain and power output of base station. The second part investigates a DS-CDMA system that employs antenna array receivers. The users are separated by different short periodic Pseudo Noise (PN) codes. The inherent spatial and temporal structure in the received user signals is exploited in order to combat Intersymbol Interference (lSI) introduced by a multi path channel as well as to mitigate MUltiple Access Interference (MAl) imposed by the multi access system. Various blind single-user receivers are presented which have only the knowledge of the PN code of the desired user. They are compared and assessed, both theoretically with a mathematical framework and practically with simulation results. It is shown how conventional time-only or space-only methods can be unified and regarded from. a space-time point of view. In particular, conventional receivers based on matched filters like, e.g., the RAKE receiver are put into a space-time context and compared to the relatively new subspacebased method, which does not entirely rely on the mutual orthogonality of the signals but exploits their linear independence. Two separate aspects of the receiver are emphasized: the estimation part, which is in charge of providing the channel parameters associated with the user of interest, and the reception part, which separates the desired from the undesired signal components based on the estimated parameters. ----- I |