Department of Computer Science and Information Systems
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Item Adaptive RIS design and optimization for cooperative ris-assisted wireless systems(IEEE, 2025-07) Bitragunta, Sainath; Bhatia, AshutoshWe propose an adaptive RIS-based cooperative transmission strategy that jointly selects one of two RIS paths and dynamically optimizes the number of active meta-atoms to maximize physical layer (PHY) secrecy capacity under a total average power constraint. Unlike existing approaches that fix the RIS size K or assume identical fading on all links, our framework uses long-term statistics to probabilistically choose between two RISs (upper or lower) with arbitrary first-hop fading, and leverages instantaneous channel state information (CSI) on the selected path to solve a convex K-sizing problem via a Lagrangian multiplier approach. We derive and present the solution for optimal K, and numerically evaluate the average PHY secrecy capacity and average PHY secrecy efficiency for the proposed optimal strategy. Numerical results show that the proposed optimal-K strategy achieves up to 35% higher average PHY secrecy capacity and 50% improvement in average PHY secrecy efficiency compared to a fixed-K benchmark strategy across moderate power thresholds. Furthermore, we present an insightful asymptotic analysis for average PHY secrecy capacity in an interesting scaling regime. Our findings demonstrate the practical benefits of adaptive RIS for cooperative PHY secure and energy-efficient beyond fifth generation (B5G) wireless systemsItem Secrecy capacity and efficiency outage analysis of cooperative phy-secure wireless systems and secrecy capacity-based RIS design(IEEE, 2025-03) Bitragunta, Sainath; Bhatia, AshutoshPhysical layer (PHY) security (PLS) leverages the inherent randomness of wireless fading channels to provide enhanced secrecy capacity. In this work, we consider a four-node, dual hop, eavesdropper-aware cooperative PHY-security model. Considering probabilistic relay selection and relaying in the presence of hybrid fading channels, we develop an insightful analysis for the probability of PHY-secrecy capacity outage (PSCO) and PHY-secrecy efficiency outage (PSEO). Specifically, we derive closed form expressions for these performance measures and evaluate them numerically to obtain valuable qualitative insights. We also develop an insightful comparative study to show that the cooperative PLS relay model having a destination node equipped with multiple antennas and performing selection combining delivers superior PHY-secrecy outage performance. We extend the analysis to the reconfigurable intelligent surface (RIS)-assisted cooperative PLS system. Specifically, we address the design problem of N, the number of reflecting elements in RIS. We develop insightful criteria based on secrecy capacity to derive a closed form lower bound on N. This insightful result provides the values of N that could achieve superior PHY-secrecy capacity than the relay-assisted cooperative PLS system. Our analysis of the former cooperative PLS model and its extension to RIS design is useful for next generation cooperative PLS relay and RIS-assisted wireless systems and networks.Item Relay Selection, Eavesdropper-Aware Relaying, PHY-Secrecy Capacity Analysis of Cooperative Wireless System over Hybrid Fading Channels(IEEE, 2023) Bhatia, Ashutosh; Bitragunta, SainathPhysical layer (PHY) security (PLS) exploits the randomness of wireless fading channels and offers better secrecy capacity. Cooperative and eavesdropper-aware relays are useful in establishing reliable and energy-efficient communication links between the source transmitter and destination receiver and enhancing PHY secrecy. We consider a four-node, two-hop cooperative PHY-security model with one eavesdropper node. For it, we propose relay selection probabilistically and relaying in the presence of hybrid fading channels. We derive closed-form expressions for probabilities with which the regenerative relay is selected. Further, we develop an analysis of PHY-secrecy capacity and gain useful insights. We evaluate and validate the performance of the proposed strategy and present different numerical results. The proposed model with the relay selection and energy-efficient relaying strategy is a useful potential benchmark for more complex power-adaptive cooperative PHY-secure systems and networks.