The aim of this paper is to characterize the impact of non-orthogonal multiple access (NOMA) on the age of information (AoI) of grant-free transmission. In particular, a low-complexity form of NOMA, termed NOMA-assisted random access, is applied to grant-free transmission in order to illustrate the two benefits of NOMA for AoI reduction, namely increasing channel access and reducing user collisions. Closed-form analytical expressions for the AoI achieved by NOMA assisted grant-free transmission are obtained, and asymptotic studies are carried out to demonstrate that the use of the simplest form of NOMA is already sufficient to reduce the AoI of orthogonal multiple access (OMA) by more than 40%. In addition, the developed analytical expressions are also shown to be useful for optimizing the users' transmission attempt probabilities, which are key parameters for grant-free transmission.

翻译：本文旨在刻画非正交多址接入（NOMA）对免授权传输信息时效性（AoI）的影响。具体而言，我们将一种低复杂度的NOMA形式——即NOMA辅助随机接入——应用于免授权传输，以阐明NOMA在降低AoI方面的两个优势：增加信道接入机会与减少用户碰撞。我们推导了NOMA辅助免授权传输所达到的AoI的闭式解析表达式，并通过渐近分析表明，即使采用最简形式的NOMA，也足以将正交多址接入（OMA）的AoI降低40%以上。此外，所建立的解析表达式还被证明可用于优化用户的传输尝试概率——这是免授权传输中的关键参数。