Full-duplex-enabled joint communications and sensing with reconfigurable intelligent surfaces

The full-duplex (FD) technology has the potential
to radically evolve wireless systems, facilitating the integration
of both communications and radar functionalities into a single
device, thus, enabling joint communication and sensing (JCAS).
In this paper, we present a novel approach for JCAS that incorporates a reconfigurable intelligent surface (RIS) in the near-field
of an FD multiple-input multiple-output (MIMO) node, which is
jointly optimized with the digital beamformers to enable JSAC
and efficiently handle self-interference (SI). We propose a novel
problem formulation for FD MIMO JCAS systems to jointly
minimize the total received power at the FD node’s radar receiver,
while maximizing the sum rate of downlink communications
subject to a Cramér-Rao bound (CRB) constraint. In contrast
to the typically used CRB in the relevant literature, we derive a
novel, more accurate, target estimation bound that fully takes into
account the RIS deployment. The considered problem is solved
using alternating optimization, which is guaranteed to converge
to a local optimum. The simulation results demonstrate that the
proposed scheme achieves significant performance improvement
both for communications and sensing. It is showcased that,
jointly designing the FD MIMO beamformers and the RIS
phase configuration to be SI aware can significantly loosen the
requirement for additional SI cancellation.