Massive Grant-Free Access With Low Latency Using User Grouping

Abstract

In future 6G networks, massive machine-type communications (mMTC) must support highly reliable and low latency uplink transmission. To address these challenges, we propose a user grouping-based data transmission scheme for grant-free mMTC scenarios. Conventional grant-free access schemes typically assume that all active devices transmit data over all available time slots, leading to high inter-user interference and significant detection complexity. In contrast, the proposed scheme divides devices into multiple groups and allocates group-specific data transmission time slots, significantly reducing the number of simultaneous transmissions per slot. This enables faster and more reliable data detection at the base station (BS) using MMSE-based algorithms, while also reducing latency by limiting per-slot detection complexity. The BS further utilizes group membership information to enhance detection performance. Simulation results show that the proposed method outperforms benchmark schemes in terms of symbol error rate (SER), particularly under diverse pilot lengths, BS antenna sizes, and device distributions. The scheme is effective in both homogeneous and heterogeneous device environments, and its low-latency, high-reliability design makes it highly suitable for massive grant-free access in 6G-enabled mMTC systems.