  Reconfigurable Intelligent Surfaces (RISs) are recently attracting a wide
interest due to their capability of tuning wireless propagation environments in
order to increase the system performance of wireless networks. In this paper, a
multiuser wireless network assisted by a RIS is studied and resource allocation
algorithms are presented for several scenarios. First of all, the problem of
channel estimation is considered, and an algorithm that permits separate
estimation of the mobile user-to-RIS and RIS-to-base stations components is
proposed. Then, for the special case of a single-user system, three possible
approaches are shown in order to optimize the Signal-to-Noise Ratio with
respect to the beamformer used at the base station and to the RIS phase shifts.
Next, for a multiuser system with two cells, assuming channel-matched
beamforming, the geometric mean of the downlink Signal-to-Interference plus
Noise Ratios across users is maximized with respect to the base stations
transmit powers and RIS phase shifts configurations. In this scenario, the RIS
is placed at the cell-edge and some users are jointly served by two base
stations to increase the system performance. Numerical results show that the
proposed procedures are effective and that the RIS brings substantial
performance improvements to wireless system.
