  We consider the optimization of a smart radio environment where meta-surfaces
are employed to improve the performance of multiuser wireless networks working
at sub-THz frequencies. Motivated by the extreme sparsity of the THz channel we
propose to model each meta-surface as an electronically steerable reflector, by
using only two parameters, regardless of its size. This assumption, although
suboptimal in a general multiuser setup, allows for a significant complexity
reduction when optimizing the environment and, despite its simplicity, is able
to provide high communication rates. We derive a set of asymptotic results
providing insight on the system behavior when both the number of antennas at
the transmitter and the meta-surfaces area grow large. For the optimization we
propose an algorithm based on the Newton-Raphson method and a simpler, yet
effective, heuristic approach based on a map associating meta-surfaces and
users. Through numerical results we provide insights on the system behavior and
we assess the performance limits of the network in terms of supported users and
spatial density of the meta-surfaces.
