Broadband beam steering for misaligned multi-mode OAM communication systems

TL;DR

This paper investigates the impact of misalignment on multi-mode OAM broadband wireless systems and demonstrates that digital beam steering significantly enhances spectral efficiency compared to analog methods, especially in large bandwidth scenarios.

Contribution

It analyzes the effects of misalignment on OAM systems and compares analog and digital beam steering, showing digital methods offer superior performance for practical broadband applications.

Findings

Misalignment severely reduces spectral efficiency in OAM systems.

Digital beam steering outperforms analog in high bandwidth and large array scenarios.

Digital transceivers with digital beam steering are more suitable for practical multi-mode OAM broadband communication.

Abstract

Orbital angular momentum (OAM) at radio frequency (RF) has attracted more and more attention as a novel approach of multiplexing a set of orthogonal OAM modes on the same frequency channel to achieve high spectral efficiency (SE). However, the precondition for maintaining the orthogonality among different OAM modes is perfect alignment of the transmit and receive uniform circular arrays (UCAs), which is difficult to be satisfied in practical wireless communication scenario. Therefore, to achieve available multi-mode OAM broadband wireless communication, we first investigate the effect of oblique angles on the transmission performance of the multi-mode OAM broadband system in the non-parallel misalignment case. Then, we compare the UCA-based RF analog and baseband digital transceiver structures and corresponding beam steering schemes. Mathematical analysis and numerical simulations validate that the SE of the misaligned multi-mode OAM broadband system is quite low, while analog and digital beam steering both can significantly improve the SE of the system. However, digital beam steering can obtain higher SE than analog beam steering especially when the bandwidth and the number of array elements are large, which validates that baseband digital transceiver with digital beam steering is more suitable for multi-mode OAM broadband wireless communication systems in practice.