On the Spectral Efficiency Limits of an OAM-based Multiplexing Scheme

TL;DR

This paper analyzes the spectral efficiency limits of Orbital Angular Momentum (OAM) multiplexing, showing it offers no advantage over traditional methods and is more sensitive to misalignments, based on Shannon capacity analysis.

Contribution

It derives the spectral efficiency limits of OAM multiplexing from Shannon capacity, comparing it to traditional methods and highlighting robustness issues.

Findings

OAM multiplexing does not outperform traditional multiplexing in spectral efficiency.

Small misalignments significantly impact OAM performance.

Traditional multiplexing is more robust to array misalignments.

Abstract

As reported in several recent publications, a spatial multiplexing involving the transmission of orthogonal waves carrying Orbital Angular Momentum (OAM) is unable to provide spectral efficiency improvements with respect to the conventional techniques. In this work we emphasize how the limits of an OAM multiple transmission between antenna arrays can be derived from the Shannon capacity formula, taking as a reference the performance of a multiplexing method based on the higher-order channel modes. Our approach clearly indicates that the two techniques offer the same on-axis performance. Conversely, small misalignments in the arrays positions affect the OAM scheme, highlighting the greater robustness of a traditional multiplexing method in the context of radio communications.