Dear All,
Dr. Rajesh Ranjan will give a seminar tomorrow (Wednesday). He is currently a postdoc at IEOR. Details of of the talk are as follows:
Date: 8th April 2026 (Wednesday)
Time: 4pm
Venue: IEOR Seminar room (2nd floor)
Title: Robust and Secure Beamforming Design for RIS/STAR-RIS-assisted MU-MIMO ISAC Systems
Abstract: RIS and STAR-RIS have emerged as novel technologies to enhance physical layer security of beyond 5G/6G wireless systems. Develop a comprehensive framework for secure multi-user multiple-input multiple-output (MU-MIMO) communications in both RIS-assisted and STAR-RIS-enabled ISAC systems under some constraints. First, consider a RIS-assisted MIMO system with non-ideal reflecting elements characterized by inherent resistance, and formulate a secrecy rate maximization problem under perfect channel state information (CSI). To efficiently solve the resulting non-convex problem, a low-complexity projected gradient method (PGM) with adaptive step size is proposed, along with a simplified design based on channel power difference maximization to reduce computational complexity. Building upon this, we extend the framework to a STAR-RIS-assisted MU-MIMO ISAC system, where a dual-function radar and communication base station simultaneously serves multiple users and performs target sensing in the presence of eavesdroppers. To address challenges such as imperfect CSI and channel uncertainty, a worst-case robust secrecy rate maximization problem is formulated to jointly designs the active transmit beamforming at the BS and the passive reflection, transmission coefficients at the STAR- RIS, restricted to the transmit power available at the BS, user quality-of-service (QoS) thresholds, sensing signal-to-interference-plus-noise ratio (SINR) requirements, maximum tolerable eavesdropping leakage, and practical phase shifts constraints. An efficient alternating optimization (AO) technique is applied to obtain tractable solutions.
Speaker Bio: Dr. Rakesh Ranjan is currently a Institute Postdoctoral Fellow (IPDF) in the Department of IEOR, IIT Bombay. He completed his Ph.D. in Electronics and Communication Engineering from IIT (ISM) Dhanbad in 2025, where his research focused on efficient phase shift optimization for reconfigurable intelligent surface (RIS)-assisted wireless systems. His research interests include RIS, simultaneous transmitting and reflecting RIS (STAR-RIS), physical layer security, and integrated sensing and communication (ISAC) for beyond-5G and 6G networks. His work primarily focuses on developing low-complexity optimization frameworks and robust beamforming techniques for secure and efficient wireless communication systems.
Regards,
Manjesh Kumar Hanawal