  Reconfigurable intelligent surface (RIS) assisted millimeter-wave (mmWave)
communication systems relying on hybrid beamforming structures are capable of
achieving high spectral efficiency at a low hardware complexity and low power
consumption. In this paper, we propose an RIS-assisted mmWave point-to-point
system relying on dynamically configured sub-array connected hybrid beamforming
structures. More explicitly, an energy-efficient analog beamformer relying on
twin-resolution phase shifters is proposed. Then, we conceive a successive
interference cancelation (SIC) based method for jointly designing the hybrid
beamforming matrix of the base station (BS) and the passive beamforming matrix
of the RIS. Specifically, the associated bandwidth-efficiency maximization
problem is transformed into a series of sub-problems, where the sub-array of
phase shifters and RIS elements are jointly optimized for maximizing each
sub-array's rate. Furthermore, a greedy method is proposed for determining the
phase shifter configuration of each sub-array. We then propose to update the
RIS elements relying on a complex circle manifold (CCM)-based method. The
proposed dynamic sub-connected structure as well as the proposed joint hybrid
and passive beamforming method strikes an attractive trade-off between the
bandwidth efficiency and power consumption. Our simulation results demonstrate
the superiority of the proposed method compared to its traditional
counterparts.
