Adaptive Three-Stage Hybrid RIS for Energy-Efficient and High-Performance Wireless Networks

Reconfigurable Intelligent Surfaces (RIS) have emerged as a transformative solution for enhancing spectral and energy efficiency in wireless networks. However, conventional RIS architectures, whether passive or active, face significant limitations due to trade-offs involving power consumption, signal amplification, and deployment complexity. This paper aims to overcome these limitations by developing an adaptive RIS architecture suitable for diverse transmission conditions. We propose a novel three-stage hybrid RIS system that dynamically switches among active, passive, and dormant modes based on channel quality and transmit power thresholds. A joint optimization framework is developed to enable adaptive mode selection, beamforming, and RIS configuration. This framework integrates mode-aware control logic and fractional programming to maximize system-wide sum-rate performance while minimizing energy consumption. Extensive simulations across varying propagation scenarios confirm that the proposed hybrid RIS outperforms conventional RIS designs in both spectral and energy efficiency. The results show that active mode yields high gains in low-power or obstructed channels, passive mode supports energy-efficient reflection under moderate conditions, and the dormant mode effectively conserves energy in high-power environments. Overall, the three-stage hybrid RIS architecture provides a robust, flexible, and high-performance solution, making it a promising candidate for future 6G wireless systems.