Security-Reliability Analysis for Adaptive Semi-Grant-Free Transmissions

Internet of Things (IoT) devices frequently encounter various challenges, including limited power, spectrum, and memory resources, as well as harsh environments conditions. Therefore, the development of an efficient transmission scheme is crucial for ensuring reliable and secure communication in IoT networks. In this article, an adaptive semi-grant-free (SGF) transmission scheme is proposed for reliable uplink nonorthogonal multiple access systems with enhanced security, in which a ratio-based user scheduling criterion and a hybrid successive interference cancellation technique are employed to suppress the activity of untrusted nodes while ensuring reliable transmission. To evaluate the superiority of the adaptive scheme, a conventional static transmission scheme and a worst-case eavesdropping scenario are used as benchmarks. Simulation results show that the adaptive scheme outperforms the conventional schemes in terms of outage and intercept probability. In addition, the closed-form results of grant-based user's and grant-free user's outage probability and untrusted node's intercept probability are derived. Compared to existing literature, this work provides a comprehensive view of security-reliability tradeoff analysis of SGF transmissions.