  Reconfigurable intelligent surface (RIS) has been regarded as a revolutionary
and promising technology owing to its powerful feature of adaptively shaping
wireless propagation environment. However, as a frequency-selective device, the
RIS can only effectively provide tunable phase-shifts for signals within a
certain frequency band. Thus, base-station (BS)-RIS-user association is an
important issue to maximize the efficiency and ability of the RIS in cellular
networks. In this paper, we consider a RIS-aided cellular network and aim to
maximize the sum-rate of downlink transmissions by designing BS-RIS-user
association as well as the active and passive beamforming of BSs and RIS,
respectively. A dynamically successive access algorithm is developed to design
the user association. During the dynamical access process, an iterative
algorithm is proposed to alternatively obtain the active and passive
beamforming. Finally, the optimal BS-RIS association is obtained by an
exhaustive search method. Simulation results illustrate the significant
performance improvement of the proposed BS-RIS-user association and beamforming
design algorithm.
