On the capacity limit of wireless channels under colored scattering

TL;DR

This paper introduces a colored scattering model showing that in correlated electromagnetic environments, the capacity of MIMO channels saturates and does not grow linearly with array size as previously believed.

Contribution

It presents a new correlated scattering model and derives the asymptotic limit of degrees of freedom, challenging the traditional linear growth assumption.

Findings

Degrees of freedom are limited by $| ext{Omega}| imes ext{min}igrace{L, 1/ extGamma}$.

Capacity saturation occurs in large arrays within correlated environments.

Linear growth of capacity is not achievable under colored scattering conditions.

Abstract

It has been generally believed that the multiple-input multiple-output (MIMO) channel capacity grows linearly with the size of antenna arrays. In terms of degrees of freedom, linear transmit and receive arrays of length $L$ in a scattering environment of total angular spread $|\Omega|$ asymptotically have $|\Omega| L$ degrees of freedom. In this paper, it is claimed that the linear increase in degrees of freedom may not be attained when scattered electromagnetic fields in the underlying scattering environment are statistically correlated. After introducing a model of correlated scattering, which is referred to as the colored scattering model, we derive the number of degrees of freedom. Unlike the uncorrelated case, the number of degrees of freedom in the colored scattering channel is asymptotically limited by $|\Omega| \cdot \min \{L, 1/\Gamma}$, where $\Gamma$ is a parameter determining the extent of correlation. In other words, for very large arrays in the colored scattering environment, degrees of freedom can get saturated to an intrinsic limit rather than increasing linearly with the array size.