Air-to-Ground Cooperative OAM Communications
Ruirui Chen, Yu Ding, Beibei Zhang, Song Li, Liping Liang
TL;DR
This work addresses the challenges of hollow-divergence and antenna misalignment in air-to-ground OAM links by proposing the Air-to-Ground Cooperative OAM Communication (ACOC) scheme. It jointly uses waist-radius optimization to place cooperative users at the OAM intensity maximum and a closed-form FBS position $(x_F,y_F,H_m)$ at the intersection of the perpendicular bisector planes of two CUGs to ensure alignment. A CU-selection procedure enforces distance and angular constraints to form two cooperative user groups (four users total), enabling two-mode OAM multiplexing in hotspot scenarios. Simulations validate the optimal FBS placement and demonstrate superior spectral efficiency (SE) of ACOC over a ground-based baseline, highlighting the practical potential of cooperative OAM in mobile aerial networks.
Abstract
For users in hotspot region, orbital angular momentum (OAM) can realize multifold increase of spectrum efficiency (SE), and the flying base station (FBS) can rapidly support the real-time communication demand. However, the hollow divergence and alignment requirement impose crucial challenges for users to achieve air-to-ground OAM communications, where there exists the line-of-sight path. Therefore, we propose the air-to-ground cooperative OAM communication (ACOC) scheme, which can realize OAM communications for users with size-limited devices. The waist radius is adjusted to guarantee the maximum intensity at the cooperative users (CUs). We derive the closed-form expression of the optimal FBS position, which satisfies the antenna alignment for two cooperative user groups (CUGs). Furthermore, the selection constraint is given to choose two CUGs composed of four CUs. Simulation results are provided to validate the optimal FBS position and the SE superiority of the proposed ACOC scheme.