A Novel RIS-Assisted Modulation Scheme

In this work, in order to achieve higher spectrum efficiency, we propose a reconfigurable intelligent surface (RIS)-assisted multi-user communication uplink system. Different from previous work in which the RIS only optimizes the phase of the incident users' signal, we propose the use of the RIS to create a virtual constellation diagram to transmit the data of an additional user. We focus on the two-user case and develop a tight approximation for the probability distribution function (PDF) of the minimum distance between constellation points of both users. Then, based on the proposed statistical distribution, we derive the analytical expressions of the average bit error rate of the considered two users. The letter also shows the trade off between the performance of two users as a function of the proposed phase shift at the RIS.