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Future cellular systems will likely employ massive bi‐dimensional arrays to improve performance by large array gain and more accurate spatial filtering, motivating the design of low‐complexity signal‐processing methods. The authors propose optimising a Kronecker‐separable beamforming filter that takes advantage of the bi‐dimensional array geometry to reduce computational costs. The Kronecker factors are obtained using two strategies: alternating optimisation and sub‐array minimum mean square error (MMSE) beamforming with Tikhonov regularisation. According to the simulation results, the proposed methods are computationally efficient but come with source recovery degradation, which becomes negligible when the sources are sufficiently separated in space. [ABSTRACT FROM AUTHOR]

With the congestion of the sub-6 GHz spectrum, the interest in massive multiple-input multiple-output (MIMO) systems operating on millimeter wave spectrum grows. In order to reduce the power consumption of such massive MIMO systems, hybrid analog/digital transceivers and application of low-resolution digital-to-analog/analog-to-digital converters have been recently proposed. In this work, we investigate the energy efficiency of quantized hybrid transmitters equipped with a fully/partially connected phase-shifting network composed of active/passive phase shifters and compare it to that of quantized digital precoders. We introduce a quantized single-user MIMO system model based on an additive quantization noise approximation considering realistic power consumption and loss models to evaluate the spectral and energy efficiencies of the transmit precoding methods. Simulation results show that partially connected hybrid precoders can be more energy-efficient compared to digital precoders, while fully connected hybrid precoders exhibit poor energy efficiency in general. Also, the topology of phase-shifting components offers an energy-spectral efficiency tradeoff: Active phase shifters provide higher data rates, while passive phase shifters maintain better energy efficiency. [ABSTRACT FROM PUBLISHER]