  The integration of sensing and communication enables wireless communication
systems to serve environment-aware applications. In this paper, we propose to
leverage sensing to enhance physical layer security (PLS) in multiuser
communication systems in the presence of a suspicious target. To this end, we
develop a two-phase framework to first estimate the location of the potential
eavesdropper by sensing and then utilize the estimated information to enhance
PLS for communication. In particular, in the first phase, a dual-functional
radar and communication (DFRC) base station (BS) exploits a sensing signal to
mitigate the sensing information uncertainty of the potential eavesdropper.
Then, in the second phase, to facilitate joint sensing and secure
communication, the DFRC BS employs beamforming and artificial noise to enhance
secure communication. The design objective is to maximize the system sum rate
while alleviating the information leakage by jointly optimizing the time
allocation and beamforming policy. Capitalizing on monotonic optimization
theory, we develop a two-layer globally optimal algorithm to reveal the
performance upper bound of the considered system. Simulation results show that
the proposed scheme achieves a significant sum rate gain over two baseline
schemes that adopt existing techniques. Moreover, our results unveil that ISAC
is a promising paradigm for enhancing secure communication in wireless
networks.
