A Primer on Near-Field Communications for Next-Generation Multiple Access

TL;DR

This paper provides a comprehensive overview of near-field communications (NFC) for next-generation multiple access, analyzing channel models, capacity limits, and beamforming techniques to enhance multiuser communication systems.

Contribution

It offers a detailed tutorial on NFC, including models, capacity analysis, and low-complexity beamforming methods, highlighting its advantages over far-field approaches for NGMA.

Findings

Near-field channel models are reviewed and simplified under various conditions.

Capacity limits of NFC-MA are derived for both uplink and downlink.

Effective low-complexity beamforming strategies are proposed for multiuser NFC systems.

Abstract

Multiple-antenna technologies are advancing toward the development of extremely large aperture arrays and the utilization of extremely high frequencies, driving the progress of next-generation multiple access (NGMA). This evolution is accompanied by the emergence of near-field communications (NFC), characterized by spherical-wave propagation, which introduces additional range dimensions to the channel and enhances system throughput. In this context, a tutorial-based primer on NFC is presented, emphasizing its applications in multiuser communications and multiple access (MA). The following areas are investigated: \romannumeral1) the commonly used near-field channel models are reviewed along with their simplifications under various near-field conditions. \romannumeral2) Building upon these models, the information-theoretic capacity limits of NFC-MA are analyzed, including the derivation of sum-rate capacity and capacity region, and their upper limits for both downlink and uplink scenarios. \romannumeral3) A detailed investigation of near-field multiuser beamforming design is presented, offering low-complexity and effective NFC-MA design methodologies in both the spatial and wavenumber (angular) domains. Throughout these investigations, near-field MA is compared with its far-field counterpart to highlight its superiority and flexibility in terms of interference management, thereby laying the groundwork for achieving NGMA.