Hybrid Mechanical and Electronic Beam Steering for Maximizing OAM Channel Capacity

TL;DR

This paper introduces a hybrid mechanical and electronic beam steering method for RF-OAM systems, significantly improving channel capacity by effectively compensating for large and small antenna misalignments.

Contribution

It proposes a novel hybrid beam steering scheme combining mechanical rotation and electronic adjustments, along with a rotatable UCA structure and optimization algorithm to maximize OAM channel capacity.

Findings

Hybrid scheme effectively compensates large misalignments.

Rotatable UCA maximizes receive SNR and capacity.

Simulation confirms improved performance over existing methods.

Abstract

Radio frequency-orbital angular momentum (RF-OAM) is a novel approach of multiplexing a set of orthogonal modes on the same frequency channel to achieve high spectrum efficiencies. Since OAM requires precise alignment of the transmit and the receive antennas, the electronic beam steering approach has been proposed for the uniform circular array (UCA)-based OAM communication system to circumvent large performance degradation induced by small antenna misalignment in practical environment. However, in the case of large-angle misalignment, the OAM channel capacity can not be effectively compensated only by the electronic beam steering. To solve this problem, we propose a hybrid mechanical and electronic beam steering scheme, in which mechanical rotating devices controlled by pulse width modulation (PWM) signals as the execution unit are utilized to eliminate the large misalignment angle, while electronic beam steering is in charge of the remaining small misalignment angle caused by perturbations. Furthermore, due to the interferometry, the receive signal-to-noise ratios (SNRs) are not uniform at the elements of the receive UCA. Therefore, a rotatable UCA structure is proposed for the OAM receiver to maximize the channel capacity, in which the simulated annealing algorithm is adopted to obtain the optimal rotation angle at first, then the servo system performs mechanical rotation, at last the electronic beam steering is adjusted accordingly. Both mathematical analysis and simulation results validate that the proposed hybrid mechanical and electronic beam steering scheme can effectively eliminate the effect of diverse misalignment errors of any practical OAM channel and maximize the OAM channel capacity.