Near-Field Multipath MIMO Channel Model for Imperfect Surface Reflection

TL;DR

This paper introduces a generalized near-field MIMO channel model for RIS-assisted systems that accounts for imperfect surface reflections, showing non-LOS components can significantly impact system performance.

Contribution

It extends existing point-scattering models to include imperfect reflections on large surfaces, providing a more accurate NF MIMO channel model for RIS-assisted communications.

Findings

Non-LOS components are often non-negligible in practical scenarios.

The proposed model accurately predicts the impact of imperfect reflections.

Non-LOS links can be essential for multiplexing gains.

Abstract

Near-field (NF) communications is receiving renewed attention in the context of passive reconfigurable intelligent surfaces (RISs) due to their potentially extremely large dimensions. Although line-of-sight (LOS) links are expected to be dominant in NF scenarios, it is not a priori obvious whether or not the impact of non-LOS components can be neglected. Furthermore, despite being weaker than the LOS link, non-LOS links may be required to achieve multiplexing gains in multi-user multiple-input multiple-output (MIMO) scenarios. In this paper, we develop a generalized statistical NF model for RIS-assisted MIMO systems that extends the widely adopted point-scattering model to account for imperfect reflections at large surfaces like walls, ceilings, and the ground. Our simulation results confirm the accuracy of the proposed model and reveal that in various practical scenarios, the impact of non-LOS components is indeed non-negligible, and thus, needs to be carefully taken into consideration.