The integration of reconfigurable intelligent surfaces (RISs) and unmanned aerial vehicles (UAVs) has emerged as a promising solution for enhancing connectivity in future wireless networks. This paper designs well-connected and resilient UAV networks by deploying and virtually partitioning multiple RISs to create multiple RIS-aided links, focusing on a link-layer perspective. The RIS-aided links are created to connect user equipment (UE) to blocked and reliable UAVs, where multiple UEs can transmit to same UAV via RIS using non-orthogonal multiple access (NOMA), granting access to UEs and maximizing network connectivity. We first derive exact and approximated closed-form expressions for signal-to-interference plus noise ratio (SINR) based on aligned and non-aligned RIS-aided beams. Then, we propose to formulate the problem of maximizing network connectivity that jointly considers (i) UE NOMA clustering, (ii) RIS-aided link selection, and (ii) virtual RIS partitioning. This problem is a computationally expensive combinatorial optimization. To tackle this problem, a two-step iterative approach, called RIS-aided NOMA, is proposed. In the first step, the UEs are clustered to the RISs according to their channel gains, while UAVs are associated to those generated clusters based on their reliability, which measures the criticality of UAVs. The second step optimally partitions the RISs to support each of the cluster members. In this step, we derive the closed-form equations for the optimal partitioning of RISs within the clusters. Simulation results demonstrate that the proposed RIS-aided NOMA yields a gain of 30% to 40%, respectively, compared to UAV traditional scheme. The finding emphasizes the potential of integrating RIS with UAV communications as a robust and reliable connectivity solution for future wireless communication systems.

翻译：可重构智能表面（RIS）与无人机（UAV）的融合已成为增强未来无线网络连接性的一种前景广阔的解决方案。本文从链路层视角出发，通过部署并虚拟划分多个RIS以构建多条RIS辅助链路，设计了一种高连通性与高弹性的无人机网络。RIS辅助链路旨在将用户设备（UE）连接至受遮挡的及可靠的无人机，其中多个UE可通过RIS使用非正交多址（NOMA）技术向同一无人机传输数据，从而为用户提供接入并最大化网络连通性。我们首先基于对齐与非对齐的RIS辅助波束，推导了信干噪比（SINR）的精确与近似闭合表达式。随后，我们提出将网络连通性最大化问题建模为一个联合优化问题，该问题综合考虑（i）UE的NOMA分簇，（ii）RIS辅助链路选择，以及（iii）RIS虚拟划分。该问题属于计算复杂度高的组合优化问题。为解决此问题，本文提出了一种称为RIS辅助NOMA的两步迭代方法。第一步，根据信道增益将UE分簇至各RIS，同时依据无人机的可靠性（用于衡量无人机关键性）将无人机与生成的簇进行关联。第二步，对RIS进行最优划分以支持每个簇内成员。在此步骤中，我们推导了簇内RIS最优划分的闭合表达式。仿真结果表明，与传统的无人机方案相比，所提出的RIS辅助NOMA方案分别实现了30%至40%的性能增益。这一发现强调了将RIS与无人机通信相结合作为未来无线通信系统一种鲁棒且可靠连接解决方案的潜力。