Path Loss of RIS-Aided Spatial Modulation With On/Off Pattern

Reconfigurable intelligent surface (RIS) is considered as a critical technology for future wireless communication networks. In this letter, we discuss the electromagnetic model of the RIS-aided spatial modulation (SM) with on/off pattern, where the induction theorem is adopted. Then, we derive the received power of the target receiver and the path loss. In the far field, we prove that the received power at the target receiver is proportional to the square of the on-state RIS elements’ number. Interestingly, this relation holds approximately in the near field. Simulation results demonstrate our conclusions, and show that the spatial energy leakage due to SM is slight if the proportion of the on-state RIS elements is not too low.