We study a scenario in which multiple uncoordinated devices aim to achieve reliable transmissions within a given time frame. The devices are intermittently active and access a shared pool of channel resources in a grant-free manner by utilizing multiple transmissions (K-repetition coding). This allows them to achieve diversity and improve the reliability within a certain latency constraint. We focus on two access methods: one where devices choose K slots at random and another one where the access patterns are deterministic and follow a specific code design, namely the Steiner System. We analyze the problem under two signal models that involve different complexity for the receiver. First, collision model is considered, where only interference-free transmissions can be used and combined. Second, a model treating interference as noise is analyzed, where the receiver is capable of utilizing all K replicas, applying maximum ratio combining (MRC). For both signal models, we investigate receivers with and without successive interference cancellation (SIC). We develop approximations and bounds for the outage probabilities that very closely match simulation results. Overall, we show that deterministic access patterns have the potential to significantly outperform random selection in terms of reliability. Furthermore, deterministic access patterns offer a simplified system design.

翻译：我们研究了一个场景：多个非协调设备旨在给定时间框架内实现可靠传输。这些设备间歇性活跃，通过利用多次传输（K重复编码）以无授权方式访问共享信道资源池。这使它们能够实现分集增益，并在特定延迟约束下提升可靠性。我们聚焦于两种接入方法：一种是设备随机选择K个时隙，另一种是接入模式具有确定性并遵循特定编码设计（即斯坦纳系统）。我们在两种涉及不同接收机复杂度的信号模型下分析该问题。首先考虑碰撞模型，该模型仅能利用无干扰的传输并进行合并。其次分析将干扰视为噪声的模型，接收机能够利用所有K个副本，应用最大比合并（MRC）。针对两种信号模型，我们分别研究了有无连续干扰消除（SIC）的接收机。我们推导出与仿真结果高度吻合的中断概率近似表达式与边界。总体而言，我们证明确定性接入模式在可靠性方面具有显著优于随机选择的潜力。此外，确定性接入模式还简化了系统设计。