Beam Domain Massive MIMO for Optical Wireless Communications with Transmit Lens

TL;DR

This paper introduces a beam domain massive MIMO system for optical wireless communications using a transmit lens, demonstrating asymptotic orthogonality of channels and proposing precoding schemes that significantly enhance sum rate performance.

Contribution

It develops a novel beam domain massive MIMO framework with a transmit lens, analyzing channel properties and designing precoding methods for optimal sum rate in optical wireless systems.

Findings

Channel vectors become orthogonal with many LEDs.

BDMA achieves asymptotic optimality for sum rate.

Proposed algorithms improve beam allocation efficiency.

Abstract

This paper presents a novel massive multiple-input multiple-output (MIMO) transmission in beam domain for optical wireless communications. The optical base station equipped with massive optical transmitters communicates with a number of user terminals (UTs) through a transmit lens. Focusing on LED transmitters, we analyze light refraction of the lens and establish a channel model for optical massive MIMO transmissions. For a large number of LEDs, channel vectors of different UTs become asymptotically orthogonal. We investigate the maximum ratio transmission and regularized zero-forcing precoding in the optical massive MIMO system, and propose a linear precoding design to maximize the sum rate. We further design the precoding when the number of transmitters grows asymptotically large, and show that beam division multiple access (BDMA) transmission achieves the asymptotically optimal performance for sum rate maximization. Unlike optical MIMO without a transmit lens, BDMA can increase the sum rate proportionally to $2K$ and $K$ under the total and per transmitter power constraints, respectively, where $K$ is the number of UTs. In the non-asymptotic case, we prove the orthogonality conditions of the optimal power allocation in beam domain and propose efficient beam allocation algorithms. Numerical results confirm the significantly improved performance of our proposed beam domain optical massive MIMO communication approaches.