  This letter investigates the physical layer security in a wireless
cooperative network where communication is assisted by a full-duplex (FD)
untrusted relay in the presence of multiple external eavesdroppers. A
cluster-based colluding eavesdropping setting is considered, where illegitimate
nodes with common interests are grouped in a cluster. In order to confuse the
different eavesdropping clusters, we consider artificial-noise-aided
beamforming at the source node. Moreover, FD relay jamming is adopted to
improve the system's security. To maintain secure communications against the
untrusted relay node, a FD destination jamming scheme is adopted. Our proposed
scheme is designed based on the channel state information of the legitimate
nodes only. Numerical results show that the optimal power allocation factor
between data and artificial noise depends on the total number of antennas of
the different colluding eavesdropping clusters.
