Thesis (Ph. D.)--University of Idaho, 2006. / Abstract. "April, 2006." Includes bibliographical references (leaves 279-288). Also available online in PDF format.

Report (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Abstract. Includes bibliographical references (leaf 26). Also available via the Internet.

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published_or_final_version / abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Wireless communication systems are limited in performance and capacity by the major impairments of multipath fading and co-channel interference. Smart antenna can combat the impairments, thereby enhancing the system capacity and alleviating the problem of bandwidth limitation. In general, there are two main types of smart antennas; these are switched beam systems and adaptive array systems. An antenna array, which consists of a group of several antenna elements and digital signal processing units, can form several independent beams in different angles. Smart antennas aim the main beam in the direction of the target mobile user and locate the nulls in the direction of the interfering signals from other mobile users to enhance the signal-to-interference power ratio and system capacity. One of the most important parts in adaptive array antenna systems is the adaptive algorithm to adjust the weights of an array. These algorithms include unconstrained as well as constrained LMS, normalized LMS, structured gradient, RLS, CMA, and conjugate gradient method. In this thesis, we propose a new algorithm based on weight-partition RLS method to reduce the computational complexity. The major concept of our algorithm is decreasing the dimension size of data matrix. Performance and complexity of the proposed algorithm is evaluated and compared with traditional WRLS algorithm.

Thesis (M.App.Sc.) - Carleton University, 2006. / Includes bibliographical references (p. 108-112). Also available in electronic format on the Internet.

The increasing demand for high data rate services necessitates the adoption of very wideband waveforms. In this case, the channel is frequency-selective, that is, a large number of resolvable multipaths are present in this environment and fading is not highly correlated across the band. Orthogonal frequency division multiplexing (OFDM) is well-known to be effective against multipath distortion. It is a multicarrier communication scheme, in which the bandwidth of the channel is divided into subcarriers and data symbols are modulated and transmitted on each subcarrier simultaneously. By inserting guard time that is longer than the delay spread of the channel, an OFDM system is able to mitigate intersymbol interference (ISI). Deploying an adaptive antenna array at the receiver can help separate the desired signal from interfering signals which originate from different spatial locations. This enhancement of signal integrity increases system capacity. In this research, we apply adaptive array algorithms to OFDM systems and study their performance in a multipath environment with the presence of interference. A novel adaptive beamforming algorithm based on the minimum mean-squared error (MMSE) criterion, which is referred to as frequency-domain beamforming, is proposed that exploits the characteristics of OFDM signals. The computational complexity of frequency-domain beamforming is also studied. Simulation results show employing an adaptive antenna array with an OFDM system significantly improves system performance when interference is present. Simulations also show that the computational complexity of the algorithm can be reduced by half without significant performance degradation. Adaptive array algorithms based on the maximum signal-to-noise ratio (MSNR) and the maximum signal-to-interference-plus-noise ratio (MSINR) criteria are also applied to adaptive vector OFDM systems (AV-OFDM). Simulation results show that the adaptive algorithm based on the MSNR criterion has superior performance in the multipath environment but performs worse than the one based on the MSINR criterion under the flat fading channel. / Master of Science