Rotatable Antenna-Enhanced Beamforming: Signal Enhancement and Interference Suppression

TL;DR

This paper addresses the limitation of fixed-orientation arrays by leveraging rotatable antennas (RA) to gain additional spatial degrees of freedom. It jointly optimizes the rotation angle vector ${\boldsymbol{\theta}}$ and the beamforming weight ${\boldsymbol{w}}$ to maximize the minimum gain across desired directions while constraining interference gains, using a single-beam closed-form solution and a multi-beam alternating optimization (AO) approach. The proposed AO framework combines SCA for weight optimization and PSO for rotation optimization, with convergence guarantees and quantified complexity. Numerical results show substantial gains over conventional FOA and isotropic approaches, including near-full array gain in favorable directions and robust interference suppression, highlighting the practical impact for RA-enhanced multi-antenna systems.

Abstract

Conventional beamforming with fixed-orientation antenna (FOA) arrays may struggle to effectively enhance signal and/or suppress interference due to significant variations in antenna directive gains over different steering angles. To break this limitation, we investigate in this paper the rotatable antenna (RA)-enhanced single/multi-beam forming by exploiting the new spatial degrees of freedom (DoFs) via antennas' rotation optimization. Specifically, the antenna rotation angle vector (ARAV) and antenna weight vector (AWV) are jointly optimized to maximize the minimum array gain over signal directions, subject to a given constraint on the maximum array gain over interference directions. For the special case of single-beam forming without interference, the optimal ARAV is derived in closed-form with the maximum ratio combining (MRC) beamformer applied to the AWV. For the general case of multi-beam forming, we propose an efficient alternating optimization (AO) algorithm to find a high-quality suboptimal solution by iteratively optimizing one of the ARAV and AWV with the other being fixed. Simulation results demonstrate that the proposed RA-based scheme can significantly outperform the traditional FOA-based and isotropic antenna (IA)-based schemes in terms of array gain.

Figures (5)

• Figure 1: Illustration of the linear RA array.
• Figure 2: Illustrations of the vertical antenna directive gains under different antenna radiation patterns, w.r.t. steering angle $\psi$.
• Figure 3: Array gain versus AoA $\psi$, with $\vartheta = 60^{\circ}$.
• Figure 4: Comparison of array gain patterns under different setups.
• Figure 5: Max-min array gain versus number of RAs, $N$.