Year: 2026
Type: article
Abstract: ABSTRACT This letter investigates the spatial separability of closely‐located users in cell‐free massive multiple‐input multiple‐output (CF‐mMIMO) systems using high‐diversity real‐world channel measurements. We evaluate the orthogonality of four closely‐located users under various CF topologies. To ensure a fair comparison, a constant aggregate number of 64 transmit antennas is maintained across all configurations. Our results demonstrate that transitioning from a co‐located to a distributed architecture significantly enhances spatial multiplexing: increasing the number of access points (APs) from one to eight reduces both the median channel correlation and the condition number by approximately 50%, while the median spectral efficiency is increased by 5%–6.7% from one to four APs. However, scaling beyond these thresholds results in a performance saturation, as additional APs contribute negligible power due to decreasing large‐scale fading coefficients. These findings suggest that excessive AP densification leads to marginal improvements, highlighting a practical trade‐off between spatial diversification and the effective signal strength of additional distributed APs.
Source: Electronics Letters
DOI: 10.1049/ell2.70734
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,590
OpenAlex ID: W7160907043