This paper proposes a secure downlink multi-user transmission scheme enabled by a flexible unmanned aerial vehicle base station (UAV-BS) and non-orthogonal multiple access (NOMA). According to their heterogeneous service requirements, multiple legitimate users are categorized as security-required users (SUs) and quality of service (QoS)-required users (QUs), while these QUs can potentially act as internal eavesdroppers which are curious about the secrecy transmissions of SUs. In such a context, our goal is to maximize the achievable minimum secrecy rate among SUs through the joint optimization of user scheduling, power allocation, and trajectory design, subject to the QoS requirements of QUs and the mobility constraint of UAV-BS. Due to the non-convexity of the problem, an efficient iterative algorithm is firstly proposed, based on the alternative optimization (AO) and successive convex approximation (SCA) methods and along with a penalty-based algorithm to deal with the introduced binary integer variables, to obtain a sub-optimal solution. Then, we propose an SUs-oriented low-complexity algorithm by taking advantage of the inherent characteristics of the optimization problem, which can efficiently reduce the computational complexity and can act as a reasonable initial solution for the previous iterative algorithm to achieve better performance. Finally, the superiority of our proposed scheme compared with the conventional orthogonal multiple access (OMA) one is validated by numerical simulation results.

中文翻译：

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无人机安全下行 NOMA 传输：以安全用户为导向的视角


本文提出了一种由灵活的无人机基站（UAV-BS）和非正交多址（NOMA）支持的安全下行链路多用户传输方案。根据其异构服务需求，多个合法用户被分类为安全要求用户（SU）和服务质量（QoS）要求用户（QU），而这些QU可能充当对保密传输感到好奇的内部窃听者SU 的数量。在这样的背景下，我们的目标是在满足QU的QoS要求和UAV-BS的移动性约束的情况下，通过用户调度、功率分配和轨迹设计的联合优化，最大化SU之间可实现的最低保密率。由于问题的非凸性，首先提出了一种基于替代优化（AO）和逐次凸逼近（SCA）方法的高效迭代算法，并结合基于惩罚的算法来处理引入的二进制整数变量，以获得次优解。然后，我们利用优化问题的固有特性提出了一种面向SU的低复杂度算法，该算法可以有效降低计算复杂度，并且可以作为先前迭代算法的合理初始解以获得更好的性能。最后，数值模拟结果验证了我们提出的方案相对于传统正交多址（OMA）方案的优越性。