RIS-Assisted Self-Interference Mitigation for IBFD.

In-band full-duplex (IBFD) technology offers a promising solution to address the demanding spectrum requirements of emerging wireless applications and use cases. Additionally, alongside the conventional reconfigurable intelligent surface (C-RIS), the simultaneously transmitting and reflecting RIS (STAR-RIS) is a promising technology that enables full-space coverage on both sides of the surface by dividing the incident signal into transmitted and reflected signals. Pairing FD with RIS technology creates new possibilities to achieve self-interference (SI) cancellation and spectral efficiency that were previously unattainable. This paper presents a novel approach leveraging C-RIS and STAR-RIS technologies in the IBFD network. Our methodology uses the C-RIS to improve SI mitigation at the FD transceiver, while the STAR-RIS serves as a connectivity enhancer for UL and DL transmissions. To fully leverage these capabilities, we propose a joint C-RIS and STAR-RIS problem, which entails optimizing the number of elements in the C-RIS to cancel out SI. At the same time, we use numerical and closed-form solutions to optimize STAR-RIS partitioning and reflection coefficient control for optimal DL and UL transmission performance in STAR-RIS's transmission and reflection modes.