BD-RIS-Assisted Heterogeneous RAN Slicing: eMBB–URLLC Rate Region Analysis
This paper investigates Beyond-Diagonal Reconfigurable Intelligent Surfaces (BD-RIS)-assisted uplink radio access network (RAN) slicing for the coexistence of enhanced Mobile Broadband (eMBB) and Ultra-Reliable Low-Latency Communications (URLLC) services. A single-input single-output (SISO) framework is considered, where heterogeneous orthogonal multiple access (H-OMA), heterogeneous non-orthogonal multiple access (H-NOMA), and heterogeneous rate-splitting multiple access (H-RSMA) are employed over a shared infrastructure. The achievable eMBB–URLLC rate region is characterized under single-connected, group-connected, and fully-connected BD-RIS architectures, considering no BD-RIS assistance, partial channel state information (CSI), full CSI, and phase noise in the BD-RIS. The results show that BD-RIS significantly enlarges the achievable rate region compared with the benchmark without BD-RIS. Under partial CSI, H-OMA exhibits greater robustness, whereas under full CSI, H-RSMA achieves the best performance due to its enhanced interference management capability. Moreover, fully-connected and group-connected BD-RIS architectures outperform the conventional single-connected design, while the group-connected structure provides a favorable tradeoff between performance and implementation complexity. Although phase noise degrades the achievable rates, H-RSMA combined with fully-connected BD-RIS remains the most effective solution. These results highlight the potential of BD-RIS-assisted RAN slicing for future wireless systems supporting heterogeneous services with stringent and conflicting quality-of-service (QoS) requirements.