An Uplink Grant-Free Access Mechanism Based on SCMA and Rateless Code for Non-Terrestrial Networks
Year: 2025
Type: conference-paper
Abstract: With the evolution toward 6G, Non-Terrestrial Networks (NTNs) are envisioned to provide seamless global coverage by integrating satellite and terrestrial infrastructures. However, conventional Hybrid Automatic Repeat reQuest (HARQ) mechanisms suffer from excessive latency and poor adaptability in NTN environments with long propagation delay and high dynamic. To address these challenges, we proposes a novel uplink grant-free access mechanism based on Sparse Code Multiple Access (SCMA) and rateless codes with iterative joint decoding in this paper. By replacing HARQ with Luby Transform (LT) codes, the need for feedback is eliminated and adaptive error correction without prior channel state information is enabled. Furthermore, we introduce a joint SCMA-rateless iterative decoding algorithm that exploits multi-user diversity and temporal diversity through message passing between SCMA detection and rateless decoding modules. Simulation results demonstrate that the proposed mechanism significantly reduces access latency by up to 62% compared to HARQ and 12% compared to cascaded decoding, while maintaining high reliability under low SNR conditions. This framework is particularly suitable for the future NTN scenarios with requirements on massive connectivity, such as aerospace telemetry, tracking, command and operation control (TTC&OC) networks and massive machine-type communications.
Language: English
Subfield: Aerospace Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W7127045268