  The wireless in-band full-duplex (IBFD) technology can in theory double the
system capacity over the conventional frequency division duplex (FDD) or
time-division duplex (TDD) alternatives. But the strong self-interference of
the IBFD can cause excessive quantization noise in the analog-to-digital
converters (ADC), which represents the hurdle for its real implementation. In
this paper, we consider employing a reconfigurable intelligent surface (RIS)
for IBFD communications. While the BS transmits and receives the signals to and
from the users simultaneously on the same frequency band, it can adjust the
reflection coefficients of the RIS to configure the wireless channel so that
the self-interference of the BS is sufficiently mitigated in the propagation
domain. Taking the impact of the quantization noise into account, we propose to
jointly design the downlink (DL) precoding matrix and the RIS coefficients to
maximize the sum of uplink (UL) and DL rates. The effectiveness of the proposed
RIS-assisted in-band full-duplex (RAIBFD) system is verified by simulation
studies, even taking into considerations that the phases of the RIS have only
finite resolution.
