Reconfigurable intelligent surface (RIS) is a new paradigm that has great
potential to achieve cost-effective, energy-efficient information modulation
for wireless transmission, by the ability to change the reflection coefficients
of the unit cells of a programmable metasurface. Nevertheless, the
electromagnetic responses of the RISs are usually only phase-adjustable, which
considerably limits the achievable rate of RIS-based transmitters. In this
paper, we propose an RIS architecture to achieve amplitude-and-phase-varying
modulation, which facilitates the design of multiple-input multiple-output
(MIMO) quadrature amplitude modulation (QAM) transmission. The hardware
constraints of the RIS and their impacts on the system design are discussed and
analyzed. Furthermore, the proposed approach is evaluated using our prototype
which implements the RIS-based MIMO-QAM transmission over the air in real time.Comment: This paper aims to investigate the feasibility of using RIS for MIMO
wireless transmission for higher-order modulation by presenting an analytical
modeling of the RIS-based system and providing experimental results from a
prototype which has been buil
