Energy efficiency of mmWave massive MIMO precoding with low-resolution DACs

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 trade-off: active phase-shifters provide higher data rates, while passive phase-shifters maintain better energy efficiency.Comment: Published in IEEE Journal of Selected Topics in Signal Processin

Multilevel governance patterns and the protection of groundwater and drinking water in Florida and the Netherlands

This paper develops a model of ‘governance’ as an aid for comparing such\ud governance structures and applies these to a particular policy arena: policies\ud on the protection of groundwater and on drinking water quality in the\ud Netherlands and Florida.\ud The research questions examined by this paper are:\ud 1. Which elements make up a governance structure?\ud 2. In what ways do these elements influence each other?\ud 3. What are the differences between the multilevel structure of protection for\ud aquifers in Florida and the Netherlands, and how do these differences\ud relate to other differences in the governance structure?\ud The analysis in this paper has shown that ‘governance’ involves more\ud elements than policy objectives and the means to implement policy. These\ud elements are not simply the sum of individual aspects but are closely\ud interlinked. We have tried to illustrate how these interrelations work. The case\ud study we used for this was the comparison between the Netherlands and\ud Florida regarding the protection of the quality of groundwater and drinking\ud water. The high degree of similarity between both states highlights the\ud differences, which exist as well. The interrelations between these differences\ud can be understood by using our hypotheses of the mechanisms by which they\ud work

Optimization of Massive Full-Dimensional MIMO for Positioning and Communication

Massive Full-Dimensional multiple-input multiple-output (FD-MIMO) base stations (BSs) have the potential to bring multiplexing and coverage gains by means of three-dimensional (3D) beamforming. Key technical challenges for their deployment include the presence of limited-resolution front ends and the acquisition of channel state information (CSI) at the BSs. This paper investigates the use of FD-MIMO BSs to provide simultaneously high-rate data communication and mobile 3D positioning in the downlink. The analysis concentrates on the problem of beamforming design by accounting for imperfect CSI acquisition via Time Division Duplex (TDD)-based training and for the finite resolution of analog-to-digital converter (ADC) and digital-to-analog converter (DAC) at the BSs. Both \textit{unstructured beamforming} and a low-complexity \textit{Kronecker beamforming} solution are considered, where for the latter the beamforming vectors are decomposed into separate azimuth and elevation components. The proposed algorithmic solutions are based on Bussgang theorem, rank-relaxation and successive convex approximation (SCA) methods. Comprehensive numerical results demonstrate that the proposed schemes can effectively cater to both data communication and positioning services, providing only minor performance degradations as compared to the more conventional cases in which either function is implemented. Moreover, the proposed low-complexity Kronecker beamforming solutions are seen to guarantee a limited performance loss in the presence of a large number of BS antennas.Comment: 30 pages, 6 figure