RIS-T and RIS-DH Enhanced Dual-Hop Relaying

This letter investigates a dual-hop relaying system enhanced by reconfigurable intelligent surfaces (RISs) deployed at the transmitter side (RIS-T) and the relay–destination link (RIS-DH). Both amplify-and-forward (AF) and decode-and-forward (DF) relaying protocols are considered. An active RIS-assisted RIS-DH configuration is additionally studied to evaluate the effect of signal amplification. Closed-form expressions for the outage probability (OP) and average bit error probability (ABEP) are derived, along with high-SNR asymptotic analysis. The results reveal the impact of RIS placement, relaying strategy, and active RIS operation. Numerical results, supported by Monte Carlo simulations, validate the analysis and show that the joint use of RIS-T and RIS-DH provides notable performance gains over conventional dual-hop relaying. The findings offer useful insights for the design of RIS-assisted dual-hop architectures in future wireless networks.