Abstract
Unlike traditional reflection-only reconfigurable intelligent surfaces (RISs), simultaneously transmitting and reflecting RISs (STAR-RISs) introduce an innovative technology. They expand the coverage area from half-space to full-space. This advancement provides new degrees of freedom (DoF) for controlling and optimizing signal propagation. This research explores the performance of the STAR-RIS in 6G wireless networks, comparing nearly passive STAR-RIS (NP-STAR) and active STAR (ASTAR) against nearly passive RIS (NP-RIS) and active RIS (ARIS) benchmarks. Through extensive simulations and deep learning (DL)-based optimization, we assess achievable data rates and spectral energy efficiency (SEE) across various system configurations, training dataset sizes, and user locations. Results show that in high-interference environments, NP-STAR configurations can sometimes exceed ASTAR implementations due to their ability to mitigate interference amplification. In addition, the deterioration in spectral energy efficiency (SEE) of active implementations compared to nearly passive ones confirms their greater consumption of energy. The exploration of STAR-RIS technology in 6G networks reveals key research gaps in prior works. These include limited studies on performance under real-world conditions, insufficient understanding of energy-spectral efficiency trade-offs, and the need for reliable DL optimization across scenarios. Practical deployment issues like power management and interference control also lack adequate research. Addressing these gaps is crucial for advancing STAR-RIS technology in this paper. This study emphasizes the importance of managing transmit power levels at base stations to control interference, with active setups particularly excelling in optimal channel conditions. Furthermore, DL approaches can effectively approximate genie-aided performance bounds with adequate training data, especially in complex channel scenarios. These insights provide practical guidance for deploying STAR-RIS technology in demanding wireless networks.