Maximizing Independent Channels and Efficiency in BTS Array Antennas via EM Degrees of Freedom

Massive multiple-input multiple-output (M-MIMO) technology has significantly advanced base station antenna design by integrating many transceivers (TRs) within antenna arrays, thereby improving network capacity and enabling the effective handling of complex multiuser scenario; however, antenna theory and antenna parameters with relevant bounds have not been adapted to this new reality. To address this gap, we propose a theoretical framework aimed at emphasizing the maximum number of independent MIMO channels that an antenna can provide in a cell and compare it with the physical upper bounds, and the latter is provided by the degrees of freedom (DoFs) of the field in the same cell. This approach allows for the definition of novel figures of merit for the quantification of antenna array performance, and the individuation of design strategies targeting the maximization of the number of independent channels, the average efficiency, and the maximum average gain within a specific cell. By exploring the DoF of the electromagnetic (EM) field, we establish the physical upper bounds for system performance. To this end, this article details the embedded element patterns (EEPs), their related efficiency correlation matrix (ECM) and cell correlation matrix (CCM), and orthogonal field modes, discussing the practical implications of these concepts for MIMO systems. The findings underscore the significance of sophisticated antenna models in enhancing network capacity, efficiency, and reliability. This article contributes to the optimization of antenna arrays in the next-generation mobile networks.