Future-Proof Physical Layer Security for 6G Multicast Systems: Relay Selection, Antenna Diversity, and Cooperative Transmission Design
Main article
Abstract
Future 6G multicast systems will carry immersive media, emergency coordination traffic, satellite-assisted services, cooperative sensing streams, and software-defined industrial control messages across heterogeneous radio environments. These services require not only high throughput but also secure transmission to many legitimate users under passive eavesdropping, mobility, blockage, and imperfect channel-state information. This paper develops a future-proof physical layer security framework for 6G multicast systems by integrating partial relay selection, antenna diversity, and cooperative transmission design. Unlike conventional multicast-security studies that focus on Rayleigh fading with fixed relay pools, the proposed framework interprets relay selection as a risk-aware and service-aware decision problem. The analysis is motivated by recent PRSF-based secure multicasting research but extends the discussion toward 6G deployment conditions such as cell-free access, reconfigurable surfaces, non-terrestrial links, and AI-assisted control. A compact analytical model is combined with a reproducible numerical experiment to study the probability of non-zero secrecy multicast capacity and secure outage probability. The results indicate that relay diversity and destination-antenna diversity jointly improve secrecy performance, while larger multicast groups, stronger eavesdropper populations, and higher target secrecy rates create measurable reliability penalties. The paper contributes a practical design roadmap that links physical layer security metrics with 6G architecture requirements, thereby offering a balanced approach to secure, scalable, and energy-aware multicast transmission.
