  This paper investigates the physical-layer security in a Virtual Antenna
Array (VAA)-aided Device- to-Device Multicast (D2DM) communication system,
where the User Equipments (UEs) who cache the common content will form a VAA
system and cooperatively multicast the content to UEs who desire it.
Specifically, with the target of securing the VAA-aided D2DM communication
under the threat of multiple eavesdroppers, we propose a secure beamforming
scheme by jointly considering the formed VAA and the Base Station (BS). For
obtaining the optimal beamforing vectors, a nonsmooth and nonconvex Weight Sum
Rate Maximization Problem (WRMP) is formulated and solved using Successive
Convex Approximation (SCA) approach. Furthermore, we consider the worst case
that eavesdroppers cooperatively form a eavesdrop VAA to enhance the
overhearing capacity. In this case, we modify the securing beamforming scheme,
formulate the corresponding WRMP and solve it using a two-level optimization.
Simulation results validate the improvements of the VAA-aided D2DM scheme in
terms of communication security compared with conventional D2DM schemes.
