Unsynchronized Reconfigurable Intelligent Surfaces with Pulse-Width-Based Design

In this correspondence, we present a reconfigurable intelligent surface (RIS) that reflects an incident signal to the desired direction, depending on the pulse width. This unique reconfigurability emerges by virtue of the transient response of the embedded nonlinear circuits within the RIS unit cells. The RIS does not need any control lines connected to the unit cells or precise synchronization with the base station, leading to reduced complexity of the RIS system yet allowing automated beamforming characteristics in accordance with the incident pulse width. To verify this scheme, an RIS system model using binary phase shift keying is considered, in which the RIS wireless link is connected to a single transmitter at the input and two receivers at the output. Numerical demonstrations show that modulated signals are received with contrasting bit-error rates in the two receivers, consistent with the aforementioned pulse-width-based beam control.