  The goal of this paper is to address the physical layer (PHY) security
problem for multi-user multi-input single-output (MU-MISO) Internet of Things
(IoT) systems in the presence of passive eavesdroppers (Eves). To this end, we
propose an artificial noise (AN)-aided rate-splitting (RS)-based secure
beamforming scheme. Our design considers the dual use of common messages and
places the research emphasis on hiding the private messages for secure
communication. In particular, leveraging AN-aided RS-based beamforming, we aim
to maximize the focused secrecy sum-rate (F-SSR) by jointly designing transmit
information and AN beamforming while satisfying the desired received
constraints for the private messages at IoT devices (IoDs), and per-antenna
transmit power constraint at base station. Then, we proposed a two-stage
algorithm to iteratively find the optimal solution. By transforming non-convex
terms into linear terms, we first reformulate the original problem as a convex
program. Next, we recast the optimization problem to an unconstrained problem
to obtain the global optimal solutions. Utilizing the duality framework, we
further develop an efficient algorithm based on a barrier interior point method
to solve the reformulated problem. Simulation results validate the superior
performance of our proposed schemes.
