Reconfigurable intelligent surface-enabled channel signature modulation

This work proposes RIS-enabled channel signature modulation (RIS-CSM), a lightweight index modulation scheme for reconfigurable intelligent surfaces (RIS). An N -element RIS is partitioned into disjoint groups, each employing predetermined binary reflection patterns to generate distinct channel signatures at an n R -antenna receiver, without RIS-side beamforming. Information is embedded in the indices of these signatures, enabling simple channel estimation and scalable spectral efficiency. A closed-form upper bound on error probability and capacity analysis are derived, revealing diversity order n R and coding gain proportional to N . Simulation results under Rayleigh fading validate the theoretical analysis. Moreover, simulations indicate that spatial correlation among RIS elements can improve system performance at low spectral efficiency.