Beam Focusing for Near-Field Multi-User MIMO Communications

TL;DR

This paper explores beam focusing in near-field multi-user MIMO systems, demonstrating its potential to enable high-rate, interference-free communication for users in the same angular direction, using various antenna architectures.

Contribution

It introduces a mathematical model for near-field channels and proposes beam focusing solutions for different antenna architectures to maximize sum-rate in multi-user MIMO systems.

Findings

Beam focusing enables interference-free communication for users in the same direction.

Proposed solutions effectively maximize sum-rate in near-field multi-user scenarios.

Simulation results confirm the feasibility of near-field beam focusing for various architectures.

Abstract

Large antenna arrays and high-frequency bands are two key features of future wireless communication systems. The combination of large-scale antennas with high transmission frequencies often results in the communicating devices operating in the near-field (Fresnel) region. In this paper, we study the potential of beam focusing, feasible in near-field operation, in facilitating high-rate multi-user downlink multiple-input multiple-output (MIMO) systems. As the ability to achieve beam focusing is dictated by the transmit antenna, we study near-field signaling considering different antenna structures, including fully-digital architectures, hybrid phase shifter-based precoders, and the emerging dynamic metasurface antenna (DMA) architecture for massive MIMO arrays. We first provide a mathematical model to characterize near-field wireless channels as well as the transmission pattern for the considered antenna architectures. Then, we formulate the beam focusing problem for the goal of maximizing the achievable sum-rate in multi-user networks. We propose efficient solutions based on the sum-rate maximization task for fully-digital, (phase shifters based-) hybrid and DMA architectures. Simulation results show the feasibility of the proposed beam focusing scheme for both single- and multi-user scenarios. In particular, the designed focused beams are such that users residing at the same angular direction can communicate reliably without interfering with each other, which is not achievable using conventional far-field beam steering.