Outage Analysis of Downlink RSMA in Vehicular Cluster: A Copula-Based Approach

The surge in on-road vehicles is fueling the need for the adoption of technologies like rate-splitting multiple access (RSMA) to meet the demand for higher data rates and enhanced quality-of-service (QoS). However, a key challenge in RSMA lies in addressing the inherent dependency between the common and private streams, which complicates outage analysis. This dependency arises not only due to interference between the streams but also from the necessity of decoding both streams for successful reception. Accurately modelling this dependency is crucial, yet it remains largely unexplored. This letter introduces a novel copula-based framework to model the dependency in downlink RSMA for vehicular clusters, where maximal ratio transmission (MRT) is used for the common stream and zero-forcing scale-down (ZF-SD) for the private streams. By deriving the analytical outage probability expressions and validating them with Monte Carlo simulations, we provide a comprehensive performance analysis. Additionally, we explore the impact of power allocation on both outage and throughput, offering practical design insights for RSMA-enabled vehicular systems.