Let Us Work Together: Cooperative Beamforming for UAV Anti-Jamming in Space-Air-Ground Networks

The satellite-air-ground networks (SAGNs) are experiencing unprecedented deployment for the advantages of global coverage and flexibility. However, the open light-of-sight communication links from satellites to the unmanned aerial vehicles (S2U) in SAGNs are vulnerable to malicious jamming and inadvertent interferences from other communication satellites, challenging the reliability of SAGNs. Despite the great importance, the anti-jamming S2U communication problem in SAGNs has been largely overlooked. To address this problem, we propose a two-stage anti-jamming scheme that embraces the cooperation among the unmanned aerial vehicles (UAVs) within the same group and jointly designs the hovering altitude of UAVs and the beamformers of satellites and cooperative UAVs to combat the malicious jamming and the cross-tier interferences. Specifically, following the proposed scheme, we formulate the problem of maximizing the minimum rate of the UAVs with the presence of the malicious jamming and inadvertent interferences into a nonconvex optimization problem. We then transform the problem into two tractable convex subproblems with feasible point pursuit successive convex approximation (FPP-SCA) method and provide the solutions to configure the hovering altitudes and the beamformers. We also conduct extensive simulations and the results show that the proposed anti-jamming scheme is efficient in terms of the UAVs' capacity and the anti-jamming ability compared with the ones without cooperative UAVs and with fixed cooperators (FixCo).