The future fifth generation (5G) systems will aim to design low-cost phased array base station antenna systems at mm-waves for simultaneous multiple beamforming with enhanced spatial multiplexing, limited interference, acceptable power consumption, suitable processing complexity, and passive cooling. In this study, a multi-user space division multiple access (SDMA) model is developed to investigate the trade-off between the quality of service (QoS), computational complexity in beamforming and

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... oling requirements for various use cases, and a number of users. The QoS at the user ends is rated by assessing the statistical signal-to-interference-plus-noise ratios (SINRs). Two beamforming algorithms, namely conjugate beamforming (CB) and zero-forcing (ZF), are considered and compared. Depending on the deployment scenario, rotated and optimised array layouts are proposed to be used in CB with the least computational complexity while providing relatively good QoS. Different reduced-complexity ZF algorithms are introduced as a compromise between the SINR performance and computational burden. The impact of the number of simultaneously served users on the thermal management in active integrated 5G base station antenna arrays is investigated as well.