# Simple Semi-Grant-Free Transmission Strategies Assisted by Non-Orthogonal Multiple Access

## TL;DR

This paper introduces NOMA-assisted semi-grant-free transmission strategies that balance grant-based and grant-free schemes, enhancing connectivity and spectral efficiency in future wireless networks.

## Contribution

It proposes novel SGF transmission mechanisms with interference control, improving user admission and network performance over traditional grant-based or grant-free methods.

## Key findings

- Effective interference suppression from grant-free users.
- Enhanced connectivity and spectral efficiency.
- Applicability of mechanisms to different network scenarios.

## Abstract

Grant-free transmission is an important feature to be supported by future wireless networks since it reduces the signalling overhead caused by conventional grant-based schemes. However, for grant-free transmission, the number of users admitted to the same channel is not caped, which can lead to a failure of multi-user detection. This paper proposes non-orthogonal multiple-access (NOMA) assisted semi-grant-free (SGF) transmission, which is a compromise between grant-free and grant-based schemes. In particular, instead of reserving channels either for grant-based users or grant-free users, we focus on an SGF communication scenario, where users are admitted to the same channel via a combination of grant-based and grant-free protocols. As a result, a channel reserved by a grant-based user can be shared by grant-free users, which improves both connectivity and spectral efficiency. Two NOMA assisted SGF contention control mechanisms are developed to ensure that, with a small amount of signalling overhead, the number of admitted grant-free users is carefully controlled and the interference from the grant-free users to the grant-based users is effectively suppressed. Analytical results are provided to demonstrate that the two proposed SGF mechanisms employing different successive interference cancelation decoding orders are applicable to different practical network scenarios.