Double-RISs Aided Receive Polarization-Combined Space Shift Keying and Spatial Modulation Systems with SPTnet-Detector

Reconfigurable intelligent surfaces (RISs) have recently attracted significant attention for improving wireless performance, yet single-RIS deployments remain limited in terms of coverage and design flexibility. To further enhance transmission reliability and link quality, we propose double RISs receive polarization and spatial shift keying (D-RPSSK) and receive polarization and spatial modulation (D-RPSM) systems over Nakagami-m fading channels, introducing a new paradigm for next-generation wireless communications. By jointly exploiting polarization and spatial diversity, the proposed architecture improves spectral utilization and enhances link robustness. Building upon the system models, the novel theoretical average bit error probability (ABEP) expressions are derived using maximum likelihood (ML) detector. Moreover, a spatial and polarization Transformer-based (SPTnet) detector is developed to capture long-range dependencies, enabling accurate symbol recovery under complex propagation environments. This integration of D RISs-assisted index modulation and deep learning (DL)–based detector effectively overcomes challenges related to spectral efficiency (SE) and bit error rate (BER) under time-varying channels. Simulation results demonstrate the superiority of the proposed D-RISs schemes, showing significant improvements in both reliability and efficiency over conventional designs and show that the proposed SPTNet achieves near-ML detector accuracy and surpasses LSTM-based detector under complex channel conditions.