Design and Implementation of MIMO Transmission through Reconfigurable Intelligent Surface

By the ability to periodically change the reflection coefficients of the unit cells of the reconfigurable intelligent surface (RIS), RIS-empowered wireless transmitter has emerged as an attractive paradigm that can achieve information modulation and transmission in a cost-effective and energy-efficient manner. However, only the phase electromagnetic response of the RISs can be flexibly manipulated in most cases, which significantly limits the transmission rate of RIS-based transmitters. In this paper, RIS-based quadrature amplitude modulation (QAM) and multiple-input multiple-output (MIMO) transmission are designed to improve the communication rate of RIS-based transmitter. In addition, our proposed method of achieving RIS-based MIMO-QAM is proved to be robust with the discrete phase shift of the RIS. Furthermore, a prototype is implemented to perform real-time RIS-based MIMO-QAM transmission over the air, which practically validates the proposed approach.