In this paper, we analyze the outage performance of unmanned aerial vehicles (UAVs)-enabled downlink non-orthogonal multiple access (NOMA) communication systems with the semi-grant-free (SGF) transmission scheme. A UAV provides coverage services for a grant-based (GB) user and one user is allowed to utilize the same channel resource opportunistically. The hybrid successive interference cancellation scheme is implemented in the downlink NOMA scenarios for the first time. The analytical expressions for the exact and asymptotic outage probability (OP) of the grant-free (GF) user are derived. The results demonstrate that no-zero diversity order can be achieved only under stringent conditions on users' quality of service requirements. Subsequently, we propose an efficient dynamic power allocation (DPA) scheme to relax such data rate constraints to address this issue. The analytical expressions for the exact and asymptotic OP of the GF user with the DPA scheme are derived. Finally, Monte Carlo simulation results are presented to validate the correctness of the derived analytical expressions and demonstrate the effects of the UAV's location and altitude on the OP of the GF user.

翻译：本文分析了采用半授权免许可（SGF）传输方案的无人机赋能下行非正交多址接入（NOMA）通信系统的中断性能。无人机为基于授权（GB）用户提供覆盖服务，并允许另一用户机会性地占用相同信道资源。本文首次在下行NOMA场景中实现混合连续干扰消除方案。推导了免许可（GF）用户精确及渐近中断概率的解析表达式。结果表明，仅在用户服务质量需求满足严格条件下才能获得非零分集阶数。针对此问题，我们提出一种高效的动态功率分配（DPA）方案以放宽数据速率约束。推导了采用DPA方案时GF用户精确及渐近中断概率的解析表达式。最后通过蒙特卡洛仿真验证了所推导解析表达式的正确性，并展示了无人机位置和高度对GF用户中断概率的影响。