A Generalized Spatial Correlation Model for 3D MIMO Channels based on the Fourier Coefficients of Power Spectrums

Previous studies have confirmed the adverse impact of fading correlation on the mutual information (MI) of two-dimensional (2D) multiple-input multiple-output (MIMO) systems. More recently, the trend is to enhance the system performance by exploiting the channel's degrees of freedom in the elevation, which necessitates the derivation and characterization of three-dimensional (3D) channels in the presence of spatial correlation. In this paper, an exact closed-form expression for the Spatial Correlation Function (SCF) is derived for 3D MIMO channels. This novel SCF is developed for a uniform linear array of antennas with nonisotropic antenna patterns. The proposed method resorts to the spherical harmonic expansion (SHE) of plane waves and the trigonometric expansion of Legendre and associated Legendre polynomials. The resulting expression depends on the underlying arbitrary angular distributions and antenna patterns through the Fourier Series (FS) coefficients of power azimuth and elevation spectrums. The novelty of the proposed method lies in the SCF being valid for any 3D propagation environment. The developed SCF determines the covariance matrices at the transmitter and the receiver that form the Kronecker channel model. In order to quantify the effects of correlation on the system performance, the information-theoretic deterministic equivalents of the MI for the Kronecker model are utilized in both mono-user and multi-user cases. Numerical results validate the proposed analytical expressions and elucidate the dependence of the system performance on azimuth and elevation angular spreads and antenna patterns. Some useful insights into the behaviour of MI as a function of downtilt angles are provided. The derived model will help evaluate the performance of correlated 3D MIMO channels in the future.Comment: Accepted in IEEE Transactions on signal processin

Multi-Antenna Array Topologies Optimization for Future Wireless Networks by Employing Particle Swarm Optimization

The purpose of this work is to design novel antenna array topologies that maximize channel capacity. Accordingly, we employ the particle swarm optimization (PSO) algorithm as an effective technique in similar electromagnetic problems. We use a novel modelling approach to derive the spatial fading correlation function by employing a generic three-dimensional (3-D) angle of arrival (AOA) model. We then employ the PSO algorithm to find the antenna array topology that maximizes the channel capacity. The use of the PSO algorithm together with the new modelling approach for the spatial correlation is sufficiently tested and verified in terms of efficiency and correctness of addressing similar type of electromagnetic problems. Moreover, the general AOA model of this work is adaptable to different propagation environments, thus our approach is very promising in this regard

Συγκριτική παρουσίαση των τεχνολογιών 5G και WiFi 6.0

Τα τελευταία χρόνια, μεγάλη σημασία έχει δοθεί στην πέμπτη γενιά ασύρματης ευρυζωνικής συνδεσιμότητας γνωστής ως 5G, η οποία υπόσχεται μια σημαντική αναβάθμιση στη ποιότητα και στη χωρητικότητα των κινητών ευρυζωνικών υπηρεσιών αλλά και ένα γενικότερο τεχνολογικό άλμα με τη παροχή μιας πληθώρας νέων δυνατοτήτων. Παραδόξως, έχει δοθεί λιγότερη προσοχή στο Wi-Fi 6, το νέο πρότυπο 802.11ax της IEEE στην οικογένεια τεχνολογιών ασύρματου τοπικού δικτύου, με χαρακτηριστικά που στοχεύουν στα ιδιωτικά, ακραία δίκτυα, υποστηρίζοντας υψηλές ταχύτητες, χαμηλή καθυστέρηση και χαμηλή ενεργειακή κατανάλωση. Αυτή η εργασία εξετάζει την καταλληλότητα των κυψελωτών και των Wi-Fi δικτύων στην παροχή υψηλής ταχύτητας ασύρματης σύνδεσης στο διαδίκτυο. Και οι δύο τεχνολογίες φιλοδοξούν να προσφέρουν σημαντικά βελτιωμένη απόδοση, πολύ πιο γρήγορη ασύρματη ευρυζωνική σύνδεση και περαιτέρω υποστήριξη για το διαδίκτυο των πραγμάτων (IoT) και τις επικοινωνίες τύπου μηχανής, τοποθετώντας τις ως τεχνικά υποκατάστατες σε πολλά σενάρια χρήσης. Και οι δύο είναι πιθανό να διαδραματίσουν σημαντικό ρόλο στο μέλλον και ταυτόχρονα να αξιοποιηθούν ως ανταγωνιστικές και συμπληρωματικές τεχνολογίες. Το 5G αναμένεται να παραμείνει η προτιμώμενη τεχνολογία για την κάλυψη μιας ευρείας περιοχής, ενώ η τεχνολογία Wi-Fi θα παραμείνει κυρίαρχη για εσωτερική χρήση, χάρη στο πολύ χαμηλότερο κόστος ανάπτυξης. Ωστόσο, τα παραδοσιακά όρια που διέκριναν τις προηγούμενες γενιές κινητών και Wi-Fi δικτύων θολώνουν, με τη παρουσία πλέον αυτών των δυο τεχνολογιών να συμβάλει στην επίτευξη του στόχου της παροχής προσιτών, αξιόπιστων, και αδιάλειπτων ασύρματων ευρυζωνικών συνδέσεων υψηλής χωρητικότητας.In recent years, significant attention has been directed toward the fifth generation of wireless broadband connectivity known as ‘5G’, currently being deployed by Mobile Network Operators. 5G promises a significant upgrade in the quality and capacity of mobile broadband services but also a more general technological leap by providing a plethora of new capabilities Surprisingly, there has been considerably less attention paid to ‘Wi-Fi 6’, the new IEEE 802.1ax standard in the family of Wireless Local Area Network technologies with features targeting private, edge-networks, supporting high speeds, low latency and low energy consumption. This work revisits the suitability of cellular and Wi-Fi in delivering high-speed wireless Internet connectivity. Both technologies aspire to deliver significantly enhanced performance, enabling each to deliver much faster wireless broadband connectivity, and provide further support for the Internet of Things and Machine-toMachine communications, positioning the two technologies as technical substitutes in many usage scenarios. We conclude that both are likely to play important roles in the future, and simultaneously serve as competitors and complements. 5G is anticipated to remain the preferred technology for wide-area coverage, while Wi-Fi 6 will remain the preferred technology for indoor use, thanks to its much lower deployment costs. However, the traditional boundaries that differentiated earlier generations of cellular and Wi-Fi are blurring. The presence of both technologies should contribute to achieving the goal of providing affordable, reliable, and seamless high-bandwidth wireless broadband connections