Semi-Grant-Free NOMA: Ergodic Rates Analysis with Random Deployed Users

TL;DR

This paper analyzes the ergodic rates of Semi-Grant-Free NOMA systems, proposing a dynamic user selection protocol and deriving closed-form expressions, revealing performance limits and linear rate growth for users.

Contribution

It introduces a novel dynamic protocol for user selection in Semi-GF NOMA and derives analytical ergodic rate expressions, enhancing understanding of system performance.

Findings

GF user has an ergodic rate upper limit.

GB user's ergodic rate increases linearly with SNR.

Analytical expressions match numerical results.

Abstract

Semi-grant-free (Semi-GF) non-orthogonal multiple access (NOMA) enables grant-free (GF) and grant-based (GB) users to share the same resource blocks, thereby balancing the connectivity and stability of communications. This letter analyzes ergodic rates of Semi-GF NOMA systems. First, this paper exploits a Semi-GF protocol, denoted as dynamic protocol, for selecting GF users into the occupied GB channels via the GB user's instantaneous received power. Under this protocol, the closed-form analytical and approximated expressions for ergodic rates are derived. The numerical results illustrate that the GF user (weak NOMA user) has a performance upper limit, while the ergodic rate of the GB user (strong NOMA user) increases linearly versus the transmit signal-to-noise ratio.