An Energy‐Tiered Clustering‐Based Blind Detector for RIS‐RSM Systems

ABSTRACT Reconfigurable intelligent surface (RIS)‐assisted received spatial modulation (RIS‐RSM) has emerged as a promising technique to enhance spectral and energy efficiency in next‐generation wireless systems. However, performing accurate signal detection without channel state information (CSI) remains a critical challenge, particularly in blind detection scenarios. In this paper, we propose a novel clustering‐based blind detector named energy‐tiered structure initialization (ETSI). The proposed method exploits the amplitude heterogeneity of modulation symbols—originating from the unequal energy levels of QAM or hybrid constellations—by partitioning the signal space into multiple energy tiers. Each receive antenna is associated with a structure prototype, representing a normalized statistical channel pattern, which is initialized using the distribution of the underlying fading model (e.g., Rayleigh) rather than instantaneous CSI. During clustering, these prototypes are iteratively refined through tier‐wise averaging of normalized signal samples, thereby enforcing structural consistency and mitigating amplitude‐induced bias. After convergence, the constellation‐aligned cluster centres are reconstructed by combining the updated prototypes with their corresponding modulation amplitudes, inherently enabling the joint detection of both the modulation symbol and the RIS‐assisted spatial index. Simulation results show that ETSI achieves around 0.5–1 dB SNR gain over amplitude–phase aware clustering under 8PSK, and about 1–1.5 dB improvement under 16QAM, while outperforming the CSI‐based greedy detector (GD) across both modulations. Moreover, ETSI achieves BER performance close to that of the perfect‐CSI maximum likelihood detector, confirming its accuracy, scalability and practical feasibility for blind RIS‐RSM detection.