  Recently, the security of Internet of Things (IoT) has been an issue of great
concern. Physical layer security methods can help IoT networks achieve
information-theoretical secrecy. Nevertheless, utilizing physical security
methods, such as artificial noise (AN) may cost extra power, which leads to low
secure energy efficiency. In this paper, the hybrid precoding technique is
employed to improve the secure energy efficiency of the IoT network. A secure
energy efficiency optimization problem is formulated for the IoT network. Due
to the non-convexity of the problem and the feasible domain, the problem is
firstly transformed into a tractable suboptimal form. Then a secure hybrid
precoding energy efficient (SEEHP) algorithm is proposed to tackle the problem.
Numerical results indicate that the proposed SEEHP algorithm achieves higher
secure energy efficiency compared with three existing physical layer security
algorithms, especially when the number of transmit antennas is large.
