A Reliable Multicast Protocol for Streaming Services in Non-Terrestrial Networks

With the increasing popularity of extended reality (XR) applications in sixth-generation (6G) communication systems, the demand for low-latency and reliable global communication is increasing. Non-terrestrial networks (NTNs) have been explored as potential solutions to meet these requirements. However, NTNs present unique challenges such as long propagation delays, satellite movement, and handovers, which make media access control (MAC) protocols a critical topic. This paper proposes an NTN reliable multicast (NTN-RM) protocol designed for networks comprising multiple low earth orbit (LEO) satellites, high-altitude platforms (HAPs), and user equipment (UE). NTN-RM employs multibeam cellularization to efficiently cover the satellite area by dividing it into independent cells and uses HAP overhearing along with non-orthogonal multiple access (NOMA) to minimize retransmission delays. Additionally, a queue control scheme was developed to ensure seamless NOMA retransmissions, and a beam angle adjustment and handover method was designed to effectively manage satellite handovers. Simulation results based on 3rd Generation Partnership Project (3GPP) releases demonstrate that NTN-RM reduces the mean latency by approximately 23% and decreases jitter by approximately 75.8% compared to the conventional LEO direct transmission method. Additionally, NTN-RM improves reliability by approximately 3.2–8.5% compared to recent reliable multicast protocols and exhibits robust network capacity as the number of UE increases from $10^{2}$ to $10^{8}$ . These results suggest that NTN-RM is a more suitable approach for reliable multicast in NTNs. Based on the latency results, a LEO satellite density greater than $5\times 10^{-6}$ LEO $/km^{2}$ is recommended for multicast applications in NTNs.