Analyzing URA Geometry for Enhanced Spatial Multiplexing and Extended Near-Field Coverage

TL;DR

This paper explores how the geometry of uniform rectangular arrays affects near-field beamfocusing and spatial multiplexing, revealing that wide or tall arrays extend coverage and improve sum rates compared to square arrays.

Contribution

It introduces the effective beamfocusing Rayleigh distance (EBRD) for generalized URAs and analyzes how array shape influences near-field beamdepth and multiplexing limits.

Findings

Wide or tall URAs maximize EBRD and coverage.

Square URAs have the narrowest beamdepth but lower sum rates.

Wide/tall URAs achieve 3.5 times higher sum rate than square URAs.

Abstract

With the deployment of large antenna arrays at high frequency bands, future wireless communication systems are likely to operate in the radiative near-field. Unlike far-field beam steering, near-field beams can be focused within a spatial region of finite depth, enabling spatial multiplexing in both the angular and range dimensions. This paper derives the beamdepth for a generalized uniform rectangular array (URA) and investigates how array geometry influences the near-field beamdepth and the limits where near-field beamfocusing is achievable. To characterize the near-field boundary in terms of beamfocusing and spatial multiplexing gains, we define the effective beamfocusing Rayleigh distance (EBRD) for a generalized URA. Our analysis reveals that while a square URA achieves the narrowest beamdepth, the EBRD is maximized for a wide or tall URA. However, despite its narrow beamdepth, a square URA may experience a reduction in multiuser sum rate due to its severely constrained EBRD. Simulation results confirm that a wide or tall URA achieves a sum rate of 3.5 X more than that of a square URA, benefiting from the extended EBRD and improved spatial multiplexing capabilities.