Joint mmWave Beamforming and RIS Phase Shift Optimization in Multi-User Group Networks Under UAV Jamming

This paper introduces a coordinated framework in which a base station (BS) and a Reconfigurable Intelligent Surfaces (RIS) jointly support their respective user groups while mitigating the impact of a Uncrewed Aerial Vehicle (UAV)-based jammer. Specifically, the RIS-assisted users rely on a reflective surface under attack from an UAV-jammer, and the BS simultaneously supports its own associated UEs alongside the RIS. We adopt an alternating optimization strategy that decomposes the original non-convex formulation into tractable subproblems using Block Coordinate Descent (BCD), thereby enabling multi-tier cooperation in complex interference environments. We frame our objective as the sum rate maximization, a metric for overall system performance, to maintain service quality and enhance robustness under severe jamming. The core of our methodology is the transformation of the resulting non-convex subproblems into tractable convex formulations via Semidefinite Programming (SDP). We employ a joint design of beamforming and phase shift optimization, whose combined effect leads to substantial performance improvements within the proposed framework. Extensive simulations and comparisons with existing algorithms demonstrate that this design achieves superior interference suppression and resource efficiency, significantly outperforming state-of-the-art baselines in sum rate, energy efficiency, UAV-jamming resilience and group-aware support for both BS- and RIS-served users.