  Reconfigurable Intelligent Surfaces (RISs) constitute the enabler for
programmable propagation of electromagnetic signals, and are lately being
considered as a candidate physical-layer technology for the demanding
connectivity, reliability, localization, and sustainability requirements of
next generation wireless communications networks. In this paper, we present
various deployment scenarios for RIS-enabled smart wireless environments that
have been recently designed by the ongoing EU H2020 RISE-6G project. The
scenarios are taxonomized according to performance objectives, in particular,
connectivity and reliability, localization and sensing, as well as
sustainability and secrecy. We identify various deployment strategies and
sketch the core architectural requirements in terms of RIS control and
signaling, depending on the RIS hardware architectures and their respective
capabilities. Furthermore, we introduce and discuss, via preliminary simulation
results and reflectarray measurements, two key novel challenges with
RIS-enabled smart wireless environments, namely, the area of influence and the
bandwidth of influence of RISs, which corroborate the need for careful
deployment and planning of this new technology.
