Robust Beamforming Design for STAR-RIS-Aided Secure SWIPT System With Bounded CSI Error

Inspired by the cutting-edge technique simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) in helping construct a cost-effective, programmable, green, invulnerable, and self-optimized Open Access Radio Network (O-RAN), in this paper, a STAR-RIS-assisted secure simultaneous wireless information and power transfer (SWIPT) system is investigated. Limited by the channel estimation technology, the robust design of this system with bounded channel estimation error is taken into consideration. By jointly designing the transmit beamforming at the access point and the transmission and reflection coefficients of STAR-RIS, a transmit power minimization problem subject to the secrecy rate constraints, energy harvesting constraint and amplitude constraints is formulated. Blocked by the coupled optimization variables and semi-infinite channel estimation errors, an alternating optimization framework along with Shur complement and S-Procedure is proposed to deal with this non-convex problem. The simulation results have proved the effectiveness of the deployment of STAR-RIS and robustness of the proposed algorithm, meanwhile, STAR-RIS can be a promising candidate to complement the construction of O-RAN.