Joint Beamforming and Phase Shifts Design for RIS-Aided Multi-User Full-Duplex Systems in Smart Cities

Area of Science:

• Wireless Communication
• Signal Processing
• Metamaterials

Background:

• Full-duplex (FD) and reconfigurable intelligent surfaces (RIS) are key technologies for enhancing wireless communication efficiency.
• RIS-aided FD systems promise increased spectral efficiency for Internet of Things (IoT) devices in smart cities.
• However, RIS can introduce loop interference (LI) that exacerbates self-interference (SI) in FD base stations, particularly in complex urban environments.

Purpose of the Study:

• To address the challenge of residual SI and LI in RIS-aided FD systems within urban outdoor environments.
• To develop an effective joint design for beamforming matrices and RIS phase shifts.
• To evaluate the proposed methods against benchmarks and demonstrate their superiority in practical scenarios.

Main Methods:

• Formulated an optimization problem considering residual SI and LI in two urban outdoor scenarios.
• Decomposed the problem into two subproblems based on variable types.
• Employed a successive convex approximation (SCA) algorithm and a soft actor-critic deep reinforcement learning (DRL) scheme for alternate optimization.
• Compared performance against RIS phase shift design benchmarks, including exhaustive search and fixed-point iteration.

Main Results:

• The proposed low-complexity algorithm achieved performance close to exhaustive search.
• The proposed algorithm significantly outperformed the fixed-point iteration scheme.
• The proposed method demonstrated superior performance in the second scenario, highlighting its advantage in complex urban settings.

Conclusions:

• The developed joint optimization approach effectively mitigates interference in RIS-aided FD systems.
• The proposed SCA and DRL-based methods offer a practical and efficient solution for urban wireless communication.
• The study confirms the significant potential of RIS-aided FD technology for smart city applications, especially in challenging outdoor environments.