Simultaneous Active and Passive Information Transfer for Reconfigurable Intelligent Surface Aided MIMO Systems
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This paper investigates the potential of reconfigurable intelligent surface (RIS) for passive information transfer in a RIS-aided multiple-input multiple-output (MIMO) system. We propose a novel technique named simultaneous active and passive information transfer (SAPIT). In SAPIT, both the transmitter (Tx) and the RIS deliver information, where the RIS information is carried through the RIS phase shifts embedded in reflected signals. We introduce the coded modulation technique at the RIS to avoid the burden of reflection pattern design in the existing approaches. The main challenge of the proposed SAPIT-MIMO transceiver is to simultaneously detect the Tx signals and the RIS phase coefficients at the receiver. To address this challenge, we introduce appropriate auxiliary variables to convert the original signal model into two linear models with respect to the Tx signals and one entry-by-entry bilinear model with respect to the RIS phase coefficients. Based on this auxiliary system, we develop a low-complexity message-passing algorithm to solve the detection problem. Furthermore, we analyze the fundamental performance limit of the proposed SAPIT-MIMO transceiver. Notably, we establish the state evolution to characterize the receiver performance in a system of a large size. Based on the SE, we further analyze the achievable sum rate of the Tx and the RIS. The rate analysis provides insights into the code design for sum-rate maximization. Numerical results are provided to validate our theoretical analysis and show the superiority of the SAPIT-MIMO transceiver over the counterpart passive beamforming scheme.
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