RIS Configuration Aging in a Time-Varying Environment

Abstract—Reconfigurable intelligent surface (RIS) is a promising technology that can increase the capacity and coverage of wireless networks. The effectiveness of a RIS is determined by its configuration, which can be made based on the information about location of the transceiver devices. In practice, there are two main types of RIS configurations: focusing the signal reflected from the RIS at the receiver location and redirecting the signal towards the receiver. Both types of RIS configuration become outdated in time due to changes in environmental parameters caused by the movement of transceiver devices and other objects in the surrounding environment. This paper examines outdating of RIS configurations made by focusing and redirection procedures in a system with spatially static transceiver devices. The paper shows that the difference in signal-to-noise ratio for the two types of configurations can reach up to 8 dB and has nonmonotonic features that can be explained by considering the near-field region of a RIS.