NOMA for Next-generation Massive IoT: Performance Potential and Technology Directions

TL;DR

This paper evaluates the potential of NOMA technology for 6G massive IoT, demonstrating its advantages over traditional OMA and proposing innovative directions for practical implementation in future networks.

Contribution

It provides a theoretical comparison of NOMA and OMA, highlighting NOMA's superiority in massive IoT scenarios, and suggests new technological approaches for 6G IoT systems.

Findings

NOMA outperforms OMA in spectral efficiency for massive IoT.

Asynchronous contention-based systems benefit most from NOMA.

Proposes practical NOMA-based techniques like joint spreading and cell-free operations.

Abstract

Broader applications of the Internet of Things (IoT) are expected in the forthcoming 6G system, although massive IoT is already a key scenario in 5G, predominantly relying on physical layer solutions inherited from 4G LTE and primarily using orthogonal multiple access (OMA). In 6G IoT, supporting a massive number of connections will be required for diverse services of the vertical sectors, prompting fundamental studies on how to improve the spectral efficiency of the system. One of the key enabling technologies is non-orthogonal multiple access (NOMA). This paper consists of two parts. In the first part, finite block length theory and the diversity order of multi-user systems will be used to show the significant potential of NOMA compared to traditional OMA. The supremacy of NOMA over OMA is particularly pronounced for asynchronous contention-based systems relying on imperfect link adaptation, which are commonly assumed for massive IoT systems. To approach these performance bounds, in the second part of the paper, several promising technology directions are proposed for 6G massive IoT, including linear spreading, joint spreading & modulation, multi-user channel coding in the context of various techniques for practical uncoordinated transmissions, cell-free operations, etc., from the perspective of NOMA.