  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's signal, we propose the use of the RIS to create a
virtual constellation diagram to transmit the data of an additional user
signal. We focus on the two-user case and develop a tight approximation for the
cumulative distribution function (CDF) of the received signal-to-noise ratio 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 paper shows the trade off between the performance of the two users
against each other as a function of the proposed phase shift at the RIS.
