  A novel semantic communication (SC)-assisted secrecy transmission framework
is proposed. In particular, the legitimate transmitter (Tx) sends the
superimposed semantic and bit stream to the legitimate receiver (Rx), where the
information may be eavesdropped by the malicious node (EVE). As the EVE merely
has the conventional bit-oriented communication structure, the semantic signal
acts as the type of beneficial information-bearing artificial noise (AN), which
not only keeps strictly confidential to the EVE but also interferes with the
EVE. The ergodic (equivalent) secrecy rate over fading wiretap channels is
maximized by jointly optimizing the transmit power, semantic-bit power
splitting ratio, and the successive interference cancellation decoding order at
the Tx, subject to both the instantaneous peak and long-term average power
constraints. To address this non-convex problem, both the optimal and
suboptimal algorithms are developed by employing the Lagrangian dual method and
the successive convex approximation method, respectively. Numerical results
show that the proposed SC-assisted secrecy transmission scheme can
significantly enhance the physical layer security compared to the baselines
using the conventional bit-oriented communication and no-information-bearing
AN. It also shows that the proposed suboptimal algorithm can achieve a
near-optimal performance.
