Massive MIMO is a Reality -- What is Next? Five Promising Research Directions for Antenna Arrays

Massive MIMO (multiple-input multiple-output) is no longer a "wild" or "promising" concept for future cellular networks - in 2018 it became a reality. Base stations (BSs) with 64 fully digital transceiver chains were commercially deployed in several countries, the key ingredients of Massive MIMO have made it into the 5G standard, the signal processing methods required to achieve unprecedented spectral efficiency have been developed, and the limitation due to pilot contamination has been resolved. Even the development of fully digital Massive MIMO arrays for mmWave frequencies - once viewed prohibitively complicated and costly - is well underway. In a few years, Massive MIMO with fully digital transceivers will be a mainstream feature at both sub-6 GHz and mmWave frequencies. In this paper, we explain how the first chapter of the Massive MIMO research saga has come to an end, while the story has just begun. The coming wide-scale deployment of BSs with massive antenna arrays opens the door to a brand new world where spatial processing capabilities are omnipresent. In addition to mobile broadband services, the antennas can be used for other communication applications, such as low-power machine-type or ultra-reliable communications, as well as non-communication applications such as radar, sensing and positioning. We outline five new Massive MIMO related research directions: Extremely large aperture arrays, Holographic Massive MIMO, Six-dimensional positioning, Large-scale MIMO radar, and Intelligent Massive MIMO.Comment: 20 pages, 9 figures, submitted to Digital Signal Processin

Research on 2×2 MIMO Channel with Truncated Laplacian Azimuth Power Spectrum

Multiple-input multiple-output (MIMO) Rayleigh fading channel with truncated Laplacian azimuth power spectrum (APS) is studied. By using the power correlation matrix of MIMO channel model and the modified Jakes simulator, into which with random phases are inserted, the effect of the azimuth spread (AS), angle of departure (AOD) and angle of arrival (AOA) on the spatial correlation coefficient and channel capacity are investigated. Numerical results show that larger AS generates smaller spatial correlation coefficient amplitude, while larger average AOD or AOA produces larger spatial correlation coefficient amplitude. The average capacity variation is comprehensively dominated by the average AOD, AOA and AS

Mimo Communication Systems with Reconfigurable Antennas

RÉSUMÉ Les antennes reconfigurables sont capables d'ajuster dynamiquement les caractéristiques de leur diagramme de rayonnement, par exemple, la forme, la direction et la polarisation, en réponse aux conditions environnementales et exigences du système. Ces antennes peuvent aussi être utilisées en conjonction avec des systèmes à entrées multiples sorties multiples (MIMO) pour améliorer davantage la capacité et la fiabilité des systèmes sans fil. Cette thèse étudie certains des problèmes dans les systèmes sans fil équipés d'antennes reconfigurables et propose des solutions pour améliorer la performance du système. Dans les systèmes sans fil utilisant des antennes reconfigurables, la performance atteignable par le système dépend fortement de la connaissance de la direction d'arrivée (DoA) des signaux souhaités et des interférences. Dans la première partie de cette thèse, nous proposons un nouvel algorithme d'estimation de la DoA pour les systèmes à entrer simple et sortie simple (SISO) qui possèdent un élément d'antenne reconfigurable au niveau du récepteur. Contrairement à un système utilisant un réseau d'antennes conventionnelles à diagramme de rayonnement fixe, où la DoA est estimée en utilisant les signaux reçus par plusieurs éléments, dans le réseau d'antennes avec l'algorithme proposé, la DoA est estimée en utilisant des signaux reçus d'un élément d'antenne unique pendant qu'il balai un ensemble de configurations de diagramme de rayonnement. Nous étudions aussi l'impact des différentes caractéristiques des diagrammes de rayonnement utilisés, tels que la largeur du faisceau de l'antenne et le nombre d'étapes de numérisation, sur l'exactitude de la DoA estimée. Dans la deuxième partie de cette thèse, nous proposons un système de MIMO faible complexité employant des antennes reconfigurables sur les canaux sélectifs en fréquence pour atténuer les êtes de trajets multiples et donc éliminer l'interférence entre symboles sans utiliser la technique de modulation multiplexage orthogonale fréquentiel (OFDM). Nous étudions aussi l'impact de la propagation et de l'antenne angulaire largeur de faisceau sur la performance du système proposé et faire la comparaison avec la performance du système MIMO-OFDM. Dans la troisième partie de cette thèse, nous fournissons des outils analytiques pour analyser la performance des systèmes sans _l MIMO équipés d'antennes reconfigurables au niveau du récepteur. Nous dérivons d'abord des expressions analytiques pour le calcul de la matrice de covariance des coefficients des signaux reçus empiétant sur un réseau d'antennes reconfigurables en tenant compte de plusieurs caractéristiques de l'antenne tels que la largeur du faisceau, l'espacement d'antenne, l'angle de pointage ainsi que le gain de l'antenne. Dans cette partie, nous considérons un récepteur MIMO reconfigurable où le diagramme de rayonnement de chaque élément d'antenne dans le réseau peut avoir des caractéristiques différentes. Nous étudions également la capacité d'un système MIMO reconfigurable en utilisant les expressions analytiques dérivées.----------ABSTRACT Reconfigurable antennas are able to dynamically adjust their radiation pattern characteristics, e.g., shape, direction and polarization, in response to environmental conditions and system requirements. These antennas can be used in conjunction with multiple-input multiple-output (MIMO) systems to further enhance the capacity and reliability of wireless networks. This dissertation studies some of the issues in wireless cellular systems equipped with reconfigurable antennas and offer solutions to enhance their performance. In wireless systems employing reconfigurable antennas, the attainable performance improvement highly depends on the knowledge of direction-of-arrival (DoA) of the desired source signals and that of the interferences. In the first part of this dissertation, we propose a novel DoA estimation algorithm for single-input single-output (SISO) system with a reconfigurable antenna element at the receiver. Unlike a conventional antenna array system with fixed radiation pattern where the DoA is estimated using the signals received by multiple elements, in the proposed algorithm, we estimate the DoA using signals collected from a set of radiation pattern states also called scanning steps. We, in addition, investigate the impact of different radiation pattern characteristics such as antenna beamwidth and number of scanning steps on the accuracy of the estimated DoA. In the second part of this dissertation, we propose a low-complexity MIMO system employing reconfigurable antennas over the frequency-selective channels to mitigate multipath effects and therefore remove inter symbol interference without using orthogonal frequency division multiplexing (OFDM) modulation. We study the impact of angular spread and antenna beamwidth on the performance of the proposed system and make comparisons with that of MIMO-OFDM system equipped with omnidirectional antennas. In the third part of this dissertation, we provide an analytical tool to analyze the performance of MIMO wireless systems equipped with reconfigurable antennas at the receiver. We first derive analytical expressions for computing the covariance matrix coefficients of the received signals impinging on a reconfigurable antenna array by taking into account several antenna characteristics such as beamwidth, antenna spacing, antenna pointing angle, and antenna gain. In this part, we consider a reconfigurable MIMO receiver where the radiation pattern of each antenna element in the array can have different characteristics. We, additionally, study the capacity of a reconfigurable MIMO system using the derived analytical expressions

Can Electromagnetic Information Theory Improve Wireless Systems? A Channel Estimation Example

Electromagnetic information theory (EIT) is an emerging interdisciplinary subject that integrates classical Maxwell electromagnetics and Shannon information theory. The goal of EIT is to uncover the information transmission mechanisms from an electromagnetic (EM) perspective in wireless systems. Existing works on EIT are mainly focused on the analysis of degrees-of-freedom (DoF), system capacity, and characteristics of the electromagnetic channel. However, these works do not clarify how EIT can improve wireless communication systems. To answer this question, in this paper, we provide a novel demonstration of the application of EIT. By integrating EM knowledge into the classical MMSE channel estimator, we observe for the first time that EIT is capable of improving the channel estimation performace. Specifically, the EM knowledge is first encoded into a spatio-temporal correlation function (STCF), which we term as the EM kernel. This EM kernel plays the role of side information to the channel estimator. Since the EM kernel takes the form of Gaussian processes (GP), we propose the EIT-based Gaussian process regression (EIT-GPR) to derive the channel estimations. In addition, since the EM kernel allows parameter tuning, we propose EM kernel learning to fit the EM kernel to channel observations. Simulation results show that the application of EIT to the channel estimator enables it to outperform traditional isotropic MMSE algorithm, thus proving the practical values of EIT.Comment: Electromagnetic information theory (EIT) is an emerging interdisciplinary subject, aiming at providing a unified analytical framework for wireless systems as well as guiding practical system design. This paper answers the question: "How can we improve wireless communication systems via EIT"