  More and more applications that require high reliability and fault tolerance
are realized with wireless network architectures and thus ultimately rely on
the wireless channels, which can be subject to impairments and blockages.
Hence, these architectures require a backup plan in the physical layer in order
to guarantee functionality, especially when safety-relevant aspects are
involved. To this end, this work proposes to utilize the reconfigurable
intelligent surface (RIS) as a resilience mechanism to counteract outages. The
advantages of RISs for such a purpose derive from their inherent addition of
alternative channel links in combination with their reconfigurability. The
major benefits are investigated in a cell-free multiple-input and
multiple-output (MIMO) setting, in which the direct channel paths are subject
to blockages. An optimization problem is formulated that includes rate
allocation with beamforming and phase shift configuration and is solved with a
resilience-aware alternating optimization approach. Numerical results show that
deploying even a randomly-configured RIS to a network reduces the performance
degradation caused by blockages. This becomes even more pronounced in the
optimized case, in which the RIS is able to potentially counteract the
performance degradation entirely. Interestingly, adding more reflecting
elements to the system brings an overall benefit for the resilience, even for
time-sensitive systems, due to the contribution of the RIS reflections, even
when unoptimized.
