Low Complexity Transmission Schemes for Future Wireless Communication Systems
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Future of mobile communication technologies is coupled with multi-antenna systems. Recent research results encourage a massive increase in the number of base station antenna elements in order to meet high data rate demands. However, at the current mobile communication frequencies (< 6 GHz), the amount of spectrum is very limited. Therefore, increase number of antenna elements and higher carrier frequencies in millimeter wavelength range need to be understood and their corresponding potentials need to be identified. Studies proposed in this work aim to identify the degree of orthogonality of millimeter wave massive MIMO channels. For this purpose, various simulation based experiments have been done which are based on the state of the art millimeter channel models. Effect of certain propagation parameters such as the probability of existence of LOS link, number of clusters, inter-antenna elements spacing and number of base station antennas in the array have been investigated. It has been found that probability of LOS link has the highest impact at the multiuser orthogonality of the multiuser channels. In general, millimeter wave massive MIMO channels are found to be low rank. Therefore, in the last part of this work a low complexity user selection algorithm is proposed. Novelty of the work is established by both performance and computational complexity comparison. Computational cost of the proposed algorithm is significantly lower than state of the art user algorithms while the sum rate performance is exactly the same as that of best user selection algorithm.