Impact of NOMA on Age of Information: A Grant-Free Transmission Perspective

TL;DR

This paper analyzes how NOMA enhances the age of information in grant-free transmission by increasing access and reducing collisions, providing analytical expressions and demonstrating significant AoI reduction over OMA.

Contribution

It introduces a low-complexity NOMA-assisted random access scheme and derives closed-form AoI expressions, showing over 40% AoI reduction compared to OMA.

Findings

NOMA-assisted grant-free transmission reduces AoI by over 40% compared to OMA.

Analytical expressions enable optimization of user transmission probabilities.

Asymptotic analysis confirms the effectiveness of simple NOMA schemes.

Abstract

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.