  Reconfigurable intelligent surfaces (RISs) have been recently considered as
one of the emerging technologies for future communication systems by leveraging
the tuning capabilities of their reflecting elements. In this paper, we
investigate the potential of an RIS-based architecture for uplink sensor data
transmission in an ultra-reliable low-latency communication (URLLC) context. In
particular, we propose an RIS-aided grant-free access scheme for an industrial
control scenario, aiming to exploit diversity and achieve improved reliability
performance. We consider two different resource allocation schemes for the
uplink transmissions, i.e., dedicated and shared slot assignment, and three
different receiver types, namely the zero-forcing, the minimum mean squared
error (MMSE), and the MMSE-successive interference cancellation receivers. Our
extensive numerical evaluation in terms of outage probability demonstrates the
gains of our approach in terms of reliability, resource efficiency, and
capacity and for different configurations of the RIS properties. An RIS-aided
grant-free access scheme combined with advanced receivers is shown to be a
well-suited option for uplink URLLC.
