Date of Award

December 2013

Degree Type

Thesis

Degree Name

Master of Science

Department

Engineering

First Advisor

Devendra Misra

Committee Members

Weizhong Wang, Mukul Goyal, Devendra Misra

Keywords

Beamformers, Receive Diversity, Space Time Coding, Transmit Diversity

Abstract

Wireless traffic is in a continuous increase and there are growing demands for wireless systems that support higher interference suppression and noise mitigation for mobile and cellular communications. Single antenna systems use frequency or time diversity to overcome the multipath fading effect as it represents a major problem that results in sever performance degradation. However, frequency diversity is inefficient in terms of bandwidth requirements and time diversity needs slow time varying channels. Space diversity has been proposed as an alternative to the former schemes where more antennas are added to the transmitter and/or receiver. Nevertheless, when multiple antennas are used; two different gains can be employed to boost system performance represented by the space diversity gains and array gain and it is not yet clear which gain has better performance as most of the published work study each one separately. Further, there is a variety of beamforming algorithms can achieve a high array gain to mitigate noise and interference. However, because each algorithm uses a different approach to achieve this goal, an ambiguity arises in some of their performance aspects as it is possible that some algorithms may have similar performance in interference suppression but varies in their capability in mitigating noise or vice versa. This may have a big impact on their performance in some environments where the interference and noise floors vary considerably and yet no study has fully addressed this problem. In this work, multiple input multiple output antenna systems were investigated using a variety of antenna configurations and algorithms to evaluate their performance under different noise and interference levels using MATLAB software modeling tools. It was found that array gain gives higher system performance in comparison with the space diversity gain and can be considered the most optimal scheme. After analyzing the performance of different beamformers, it was found that phase shift and MVDR beamformers both have the same capability in mitigating white noise while they vary in their ability in interference suppression depending on the level of SINR of the surrounding environment. Also, Frost beamformer shows high interference suppression while its noise mitigation capability is very low which limits its use in applications where the noise floor is higher than the interference floor.

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