In this work, we study a multi-user NTN in which a satellite serves as the primary network and a high-altitude platform station (HAPS) operates as the secondary network, acting as a cognitive radio. To reduce the cost, complexity, and power consumption of conventional antenna arrays, we equip the HAPS with a transmissive BD-RIS antenna front end. We then formulate a joint optimization problem for the BD-RIS phase response and the HAPS transmit power allocation under strict per-user interference temperature constraints. To tackle the resulting highly nonconvex problem, we propose an alternating-optimization framework: the power-allocation subproblem admits a closed-form, water-filling-type solution derived from the Karush-Kuhn-Tucker (KKT) conditions, while the BD-RIS configuration is refined via Riemannian manifold optimization. Simulation results show significant gains in data rate and interference suppression over diagonal RIS-assisted benchmarks, establishing BD-RIS as a promising enabler for future multilayer NTNs.
Active RIS-Empowered Covert Satellite-Terrestrial Communications
College of Computer Science and Technology, Key Laboratory of Symbolic Computation and Knowledge Engineering of Ministry of Education, Jilin University（吉林大学计算机科学与技术学院、教育部符号计算与知识工程重点实验室）；Auburn University（奥本大学）；School of Electrical and Computer Engineering, University of Sydney（悉尼大学电气与计算机工程学院）；Graduate School of Information Sciences, Tohoku University（东北大学情报科学研究院）
Joint Visibility Analysis of RIS in Non-Terrestrial Networks through Stochastic Geometry
IMT-Télécom Paris, Institut Polytechnic de Paris（IMT-电信巴黎学院，巴黎理工学院）；School of AI Convergence, Sungshin Women’s University（顺天女子大学人工智能融合学院）；INRIA/ ENS and Télécom Paris（法国国家信息与自动化研究所/巴黎高等师范学院与电信巴黎学院）
Deep Reinforcement Learning for Interference Suppression in RIS-Aided Space-Air-Ground Integrated Networks
Department of Artificial Intelligence, Indian Institute of Technology Hyderabad, Telangana, India（印度海得拉巴印度理工学院人工智能系）；School of Informatics, Kami, Kochi University of Technology, Kochi, Japan（日本科技大学信息学院）；Graduate School of Information Sciences, Tohoku University, Sendai, Miyagi, Japan（东北大学信息科学研究生院）
Carbon-Aware Orchestration of Integrated Satellite Aerial Terrestrial Networks via Digital Twin
College of Electronics and Information Engineering, Tongji University（同济大学电子与信息工程学院）；State Key Laboratory of Autonomous Intelligent Unmanned Systems, Tongji University（同济大学自主智能无人系统国家重点实验室）；Department of Electrical and Communication Engineering, College of Engineering, UAE University（阿联酋大学电气与通信工程系）
