Reconfigurable Intelligent Surface for Industrial Automation: mmWave Propagation Measurement, Simulation, and Control Algorithm Requirements

Reconfigurable intelligent surfaces (RISs) can provide a reliable and low-latency millimeter wave (mmWave) communication link in cases of a blocked line-of-sight (LoS) between the base station (BS) and the user equipment (UE). In such cases, the RIS mounted on a wall or ceiling can act as a bypass for the radio communication link. We present an active RIS with 127 patch antenna elements arranged in a hexagonal grid. The RIS operates at a center frequency of 23.8 GHz and each RIS element uses an orthogonal polarization transformation to enable amplification using a field-effect transistor (FET). The source and drain voltages of each FET are controlled using two bits. We consider that the RIS control unit is aware of the UE coordinates within the measurement area, relevant to the industrial control scenarios. We measure the received power on a 2D grid of $60 \mathrm{~cm} \times 90 \mathrm{~cm}$ using an $x y$-positioning table, with the RIS working in reflective and active mode. The results demonstrate the ability of the RIS to effectively focus the radio signal on the desired target points. We characterize the halfpower beam width in azimuth and radial directions with respect to the RIS position, enabling us to obtain a practical RIS configuration update criterion for a mobile UE. These results clearly show that RISs are prominent solutions for enabling reliable wireless communication in indoor industrial scenarios.