Performance Analysis Of Spatial And Frequency Domain Index-Modulated Reconfigurable Intelligent Metasurfaces

Higher spectral and energy efficiencies are the envisioned defining characteristics of next-generation high data-rate sixth-generation (6G) wireless networks. One of the enabling technologies to meet these requirements is index modulation (IM), which transmits information through permutations of indices of spatial, frequency, or temporal media. In this paper, we propose novel electromagnetics-compliant designs of reconfigurable intelligent surface (RIS) apertures for realizing IM in 6G transceivers. We consider RIS modeling and implementation of spatial and subcarrier IMs, including beam steering, spatial multiplexing, and phase modulation capabilities. Numerical experiments for our proposed implementations show that the bit-error-rates obtained via RIS-aided IM outperform traditional implementations. We further establish the programmable ability of these transceivers to vary the reflection phase and generate frequency harmonics for IM through full-wave electromagnetic analyses of a specific reflect-array metasurface implementation.