Semi-grant-free (SGF) transmission scheme enables grant-free (GF) users to utilize resource blocks allocated for grant-based (GB) users while maintaining the quality of service of GB users. This work investigates the secrecy performance of non-orthogonal multiple access (NOMA)-aided SGF systems. First, analytical expressions for the exact and asymptotic secrecy outage probability (SOP) of NOMA-aided SGF systems with a single GF user are derived. Then, the SGF systems with multiple GF users and the best-user scheduling scheme is considered. Analytical expressions for the exact and asymptotic SOP are derived by utilizing order statistics theory. Monte Carlo simulation results are provided and compared with two benchmark schemes. The effects of system parameters on the SOP of the considered system are demonstrated and the accuracy of the developed analytical results is verified. The results indicate that both the outage target rate for GB and the secure target rate for GF are the main factors of the secrecy performance of SGF systems.

翻译：半免授权（SGF）传输方案允许免授权（GF）用户利用分配给基于授权（GB）用户的资源块，同时维持GB用户的服务质量。本文研究了非正交多址接入（NOMA）辅助的SGF系统的保密性能。首先，推导了单GF用户场景下NOMA辅助SGF系统的精确和渐近保密中断概率（SOP）解析表达式。接着，考虑了多GF用户场景及最佳用户调度方案，利用次序统计理论推导了精确和渐近SOP解析表达式。提供了蒙特卡洛仿真结果，并与两种基准方案进行了对比。展示了系统参数对SOP的影响，验证了所提解析结果的准确性。结果表明，GB用户的中断目标速率和GF用户的保密目标速率是影响SGF系统保密性能的主要因素。