Multi-user cooperative receive scheme for air-to-ground vortex wave communications

Orbital angular momentum (OAM) can achieve multifold increase of spectrum efficiency, but the hollow divergence characteristic and Line-of-Sight (LoS) path requirement impose the crucial challenges for vortex wave communications. For air-to-ground vortex wave communications, where there exists the LoS path, this paper proposes a multi-user cooperative receive (MUCR) scheme to break through the communication distance limitation caused by the characteristic of vortex wave hollow divergence. In particular, we derive the optimal radial position corresponding to the maximum intensity, which is used to adjust the waist radius. Based on the waist radius and energy ring, the cooperative ground users having the minimum angular square difference are selected. Also, the signal compensation scheme is proposed to decompose OAM signals in air-to-ground vortex wave communications. Simulation results are presented to verify the superiority of our proposed MUCR scheme.