Performance Evaluation of Dual RIS-Assisted Received Space Shift Keying Modulation

Abstract

Reconfigurable intelligent surfaces (RISs) are gaining traction for their ability to reshape wireless environments with low energy consumption. However, prior studies primarily explore single-RIS deployments with static or semi-static reflection control. In this paper, we propose a novel dual-RIS-assisted architecture for smart indoor wireless signal routing, wherein the second RIS (RIS-2) is dynamically configured based on source data bits to steer signals toward specific receivers or indoor zones. The first RIS (RIS-1), positioned near a fed antenna or access point, passively reflects the incident signal. RIS-2, equipped with a lightweight controller, performs bit-driven spatial modulation to enable data-dependent direction selection at the physical layer. We develop a complete end-to-end system model, including multi-hop channel representation, RIS phase configuration, and signal detection based on space shift keying (SSK). Furthermore, we incorporate practical RIS phase imperfections using Gaussian and Von Mises error models, and derive an upper-bound approximation for the ergodic capacity under large-scale RIS assumptions. The Gaussian approximation is validated numerically, and Monte Carlo simulations are conducted to assess the impact of key system parameters. Results demonstrate the scalability and flexibility of the proposed dual-RIS-assisted RSSK architecture.