Electromagnetic Effective-Degree-of-Freedom Limit of a MIMO System in 2-D Inhomogeneous Environment

TL;DR

This paper investigates the electromagnetic effective degrees of freedom (EDOF) limit of MIMO systems in 2-D inhomogeneous environments using full-wave numerical methods, revealing the relationship between system performance and environmental scattering.

Contribution

It introduces a volume integral equation approach to rigorously analyze the EDOF limit of MIMO in complex environments, extending beyond approximate models.

Findings

EDOF limit depends on environmental scattering characteristics

Full-wave numerical methods provide accurate EDOF estimates in inhomogeneous environments

Relationship between MIMO performance and environment scattering is clarified

Abstract

Compared with a single-input-single-output (SISO) wireless communication system, the benefit of multiple-input-multiple-output (MIMO) technology originates from its extra degree of freedom (DOF), also referred as scattering channels or spatial electromagnetic (EM) modes, brought by spatial multiplexing. When the physical sizes of transmitting and receiving arrays are fixed, and there are sufficient antennas (typically with half-wavelength spacings), the DOF limit is only dependent on the propagating environment. Analytical methods can be used to estimate this limit in free space, and some approximate models are adopted in stochastic environments, such as Clarke's model and Ray-tracing methods. However, this DOF limit in an certain inhomogeneous environment has not been well discussed with rigorous full-wave numerical methods. In this work, volume integral equation (VIE) is implemented for investigating the limit of MIMO effective degree of freedom (EDOF) in three representative two-dimensional (2-D) inhomogeneous environments. Moreover, we clarify the relation between the performance of a MIMO system and the scattering characteristics of its propagating environment.