  Reconfigurable Intelligent Surface (RIS) draws great attentions in academic
and industry due to its passive and low power consumption nature, and has
currently been used in physical layer security to enhance the secure
transmission. However, due to the existence of double fading effect on the
reflecting channel link between transmitter and user, RIS helps achieve limited
secrecy performance gain compared with the case without RIS. In this
correspondence, we propose a novel active RIS design to enhance the secure
wireless transmission, where the reflecting elements in RIS not only adjust the
phase shift but also amplify the amplitude of signals. To solve the non convex
secrecy rate optimization based on this design, an efficient alternating
optimization algorithm is proposed to jointly optimize the beamformer at
transmitter and reflecting coefficient matrix at RIS. Simulation results show
that with the aid of active RIS design, the impact of double fading effect can
be effectively relieved, resulting in a significantly higher secrecy
performance gain compared with existing solutions with passive RIS and without
RIS design.
