Based on worst-case performance optimization, the recently developed adaptive beamformers utilize the uncertainty set of the desired array steering vector to achieve robustness against steering vector mismatches. In the presence of large steering vector mismatches, the uncertainty set has to expand to accommodate the increased error. This degrades the output signal-to-interference-plus-noise ratios (SINRs) of these beamformers since their interference-plus-noise suppression abilities are weakened. In this paper, an iterative robust minimum variance beamformer (IRMVB) is proposed which uses a small uncertainty sphere (and a small flat ellipsoid) to search for the desired array steering vector iteratively. This preserves the interference-plus-noise suppression ability of the proposed beamformer and results in a higher output SINR. Theoretical analysis and simulation results are presented to show the effectiveness of the proposed beamformer.Index Terms-Adaptive arrays, array signal processing, interference suppression, robustness.
Abstract-Although small cell networks are environmentally friendly and can potentially improve the coverage and capacity of cellular layers, it is imperative to control the interference in such networks before overlaying them in a macrocell network on a large-scale basis. In recent work, we developed the joint admission and power control algorithm for two-tier small cell networks in which the number of small cell users that can be admitted at their quality-of-service (QoS) constraints is maximized without violating the macrocell users' QoS constraints. The QoS metric adopted is outage probability. In this paper, we investigate the distributed implementation of the joint admission and power control problem where the small cells can determine jointly their admissibility and transmit powers autonomously.
In vertical sectorization, multiple antenna elements form two beams to better serve users based on their locations in the cell. However, it is not known how to choose the radio network parameters to ensure good network performance and the amount of capacity gain achievable with vertical sectorization. In this paper, we propose an optimization approach based on the Taguchi's method for vertical sectorization deployment in order to improve the 50%-tile and 5%-tile user throughput. Unlike conventional works, our proposal is a scientifically disciplined approach optimizing jointly the downtilt angles, vertical beamwidths, and transmit powers of the two beams and taking into account the interaction amongst these network parameters. With the proposed method, the resulting 50%-tile and 5%-tile user throughput and the total network throughput outperform those of the conventional networks without vertical sectorization.
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