User Cooperative Receiving Scheme of Misaligned OAM Signals for UAV Emergency Communications

For the massive users in post-disaster scenario, unmanned aerial vehicle (UAV) can rapidly establish emergency communications, and orbital angular momentum (OAM) can significantly improve spectrum efficiency (SE). Due to hollow divergence and alignment requirement, it is hard for users to receive OAM signals by using antenna-limited devices. For UAV emergency communications with line-of-sight link, we propose the user cooperative receiving (UCR) scheme, which can realize 2 OAM mode multiplexing communications for users at long distance. Two cooperative users (CUs) are chosen, and the waist radius is adjusted to guarantee the maximum intensity at two CUs. The OAM beam steering is designed to eliminate the inter-mode interference of misaligned OAM signals caused by the antenna misalignment. Simulation results demonstrate that the proposed UCR scheme can obtain higher SE than the traditional scheme due to the effective reception of misaligned OAM signals for UAV emergency communications.