RIS-Enhanced Hybrid THz/RF Systems for 6G Networks Over Generalized Fading

Terahertz (THz) communication, a key enabler for 6 G networks, suffers from high path loss and limited coverage. To address these challenges, this paper proposes a RIS-assisted hybrid THz/RF architecture that integrates RIS with THz and radio frequency (RF) links, aiming to combine the high-capacity advantage of THz with the reliability of RF. To this end, a dynamic threshold switching (DTS) scheme is introduced, enabling real-time selection between THz and RF links based on the instantaneous signal-to-noise ratio. A complete analytical framework is developed, incorporating hardware impairments, pointing errors, and generalized$\alpha -\mu$fading in both RF and THz domains. The model incorporates deterministic RIS gains and frequency-dependent THz absorption, offering practical insights into the joint impact of RIS geometry, beam width, and switching thresholds. Closed-form expressions for outage probability, symbol error rate, ergodic capacity, and energy efficiency are derived. Simulation results confirm the accuracy of the proposed model and demonstrate that the hybrid system outperforms single-band THz or RF links and traditional diversity combining schemes. Additionally, increasing RIS elements improves performance and reduces transmit power requirements, with energy efficiency trends identifying optimal RIS configurations for practical deployment. These findings establish RIS-assisted hybrid THz/RF systems as a key enabler of reliable, high-capacity 6G communication for autonomous vehicles and smart factories.