Semi-Grant-Free NOMA: A Stochastic Geometry Model

TL;DR

This paper models semi-grant-free NOMA networks using stochastic geometry, proposing a dynamic protocol for user pairing that improves outage performance and reduces interference compared to fixed threshold methods.

Contribution

It introduces a novel dynamic protocol for semi-GF NOMA, providing a more accurate user pairing mechanism and analyzing its impact on network performance.

Findings

Dynamic protocol reduces interference significantly.

Outage performance is improved with the dynamic protocol.

The proposed model enhances spectral efficiency in uplink NOMA networks.

Abstract

Grant-free (GF) transmission holds promise in terms of low latency communication by directly transmitting messages without waiting for any permissions. However, collision situations may frequently happen when limited spectrum is occupied by numerous GF users. The non-orthogonal multiple access (NOMA) technique can be a promising solution to achieve massive connectivity and fewer collisions for GF transmission by multiplexing users in power domain. We utilize a semi-grant-free (semi-GF) NOMA scheme for enhancing network connectivity and spectral efficiency by enabling grant-based (GB) and GF users to share the same spectrum resources. With the aid of semi-GF protocols, uplink NOMA networks are investigated by invoking stochastic geometry techniques. We propose a novel \textit{dynamic protocol} to interpret which part of the GF users are paired in NOMA transmissions via transmitting various channel quality thresholds by an added handshake. We utilize open-loop protocol with a fixed average threshold as the benchmark to investigate performance improvement. It is observed that dynamic protocol provides more accurate channel quality thresholds than open-loop protocol, thereby the interference from the GF users is reduced to a large extent. We analyze the outage performance and diversity gains under two protocols. Numerical results demonstrate that dynamic protocol is capable of enhancing the outage performance than open-loop protocol.