New Phase Configuration Design Algorithms for Mid- to High-Order RIS-Assisted SSK Modulation With Passive Beamforming

This letter presents a new phase configuration design scheme, along with two algorithms, for reconfigurable intelligent surface (RIS)-assisted space shift keying (SSK) modulation with passive beamforming. In the proposed scheme, the phase configuration design problem is linked to a RIS partitioning problem, allowing the phases of RIS elements to be designed such that the noiseless signal received from each SSK mode closely matches a point in a predefined multi-level constellation. Additionally, the proposed design enables RIS adjustments at a rate inversely proportional to the channel coherence time, rather than the symbol rate, significantly enhancing the practicality of RIS-assisted SSK systems. The superior performance of the proposed scheme, compared to benchmark methods, is validated through extensive numerical simulations.