Q-RSMA Based UAV-Assisted Vehicular Cooperation: A Finite Blocklength Perspective

The rising demand for ultra-reliable and low-latency communication (URLLC) in vehicular networks calls for solutions beyond traditional cooperative schemes. Next-generation multiple access techniques, such as rate-splitting multiple access (RSMA), offer a promising path to meet these stringent requirements. However, conventional RSMA-based cooperation systems suffer from error propagation due to successive interference cancellation (SIC). To mitigate this, we propose a novel quadrature rate-splitting aided multi-user cooperative (QRSMUC) system, where an unmanned aerial vehicle (UAV) serves as a relay and employs quadrature rate-splitting multiple access (Q-RSMA) as the relaying scheme. Unlike conventional RSMA-based cooperation, Q-RSMA eliminates SIC by orthogonally transmitting common and private streams, thereby enhancing spectral efficiency and reducing error propagation. To better align with the latency and reliability demands of next-generation vehicles (NGVs), we analyze the proposed system under a finite blocklength (FBL) regime, considering both perfect channel state information (pCSI) and imperfect channel state information (ipCSI) to capture realistic short-packet communication scenarios. An end-to-end analytical framework of the average block error rate (ABLER) is developed. The proposed QRSMUC system is compared with other systems across various metrics like ABLER, latency and reliability. The results obtained in MATLAB reveal that QRSMUC outperforms the existing benchmarks and achieves the URLLC conditions of 1 msec latency and 99.99% reliability at lower power levels. These results demonstrate the proposed system's strong potential in meeting the stringent quality-of-service (QoS) requirements of NGVs and other URLLC application scenarios.