  Full duplex (FD) radio has attracted extensive attention due to its co-time
and co-frequency transceiving capability. {However, the potential gain brought
by FD radios is closely related to the management of self-interference (SI),
which imposes high or even stringent requirements on SI cancellation (SIC)
techniques. When the FD deployment evolves into next-generation mobile
networking, the SI problem becomes more complicated, significantly limiting its
potential gains.} In this paper, we conceive a multi-cell FD networking scheme
by deploying a reconfigurable intelligent surface (RIS) at the cell boundary to
configure the radio environment proactively. To achieve the full potential of
the system, we aim to maximize the sum rate (SR) of multiple cells by jointly
optimizing the transmit precoding (TPC) matrices at FD base stations (BSs) and
users and the phase shift matrix at RIS. Since the original problem is
non-convex, we reformulate and decouple it into a pair of subproblems by
utilizing the relationship between the SR and minimum mean square error (MMSE).
The optimal solutions of TPC matrices are obtained in closed form, while both
complex circle manifold (CCM) and successive convex approximation (SCA) based
algorithms are developed to resolve the phase shift matrix suboptimally. Our
simulation results show that introducing an RIS into an FD networking system
not only improves the overall SR significantly but also enhances the cell edge
performance prominently. More importantly, we validate that the RIS deployment
with optimized phase shifts can reduce the requirement for SIC and the number
of BS antennas, which further reduces the hardware cost and power consumption,
especially with a sufficient number of reflecting elements. As a result, the
utilization of an RIS enables the originally cumbersome FD networking system to
become efficient and practical.
