An effective way to realize non-orthogonal multiple access (NOMA) assisted grant-free transmission is to first create multiple receive signal-to-noise ratio (SNR) levels and then serve multiple grant-free users by employing these SNR levels as bandwidth resources. These SNR levels need to be pre-configured prior to the grant-free transmission and have great impact on the performance of grant-free networks. The aim of this letter is to illustrate different designs for configuring the SNR levels and investigate their impact on the performance of grant-free transmission, where age-of-information is used as the performance metric. The presented analytical and simulation results demonstrate the performance gain achieved by NOMA over orthogonal multiple access, and also reveal the relative merits of the considered designs for pre-configured SNR levels.

翻译：实现非正交多址（NOMA）辅助免授权传输的有效方法是：先创建多个接收信号噪声比（SNR）层级，再将这些SNR层级作为带宽资源服务于多个免授权用户。这些SNR层级需要在免授权传输开始前预先配置，并对免授权网络的性能产生重要影响。本文旨在阐述配置SNR层级的不同设计方案，并以信息年龄为性能指标，研究其对免授权传输性能的影响。仿真与分析结果表明，与正交多址相比，NOMA能带来显著的性能增益，同时揭示了所考虑的预配置SNR层级设计方案的相对优势。