  In this paper, we consider an unmanned aerial vehicle (UAV) assisted
communications system, including two cooperative UAVs, a wireless-powered
ground destination node leveraging simultaneous wireless information and power
transfer (SWIPT) technique, and a terrestrial passive eavesdropper. One UAV
delivers confidential information to destination and the other sends jamming
signals to against eavesdropping and assist destination with energy harvesting.
Assuming UAVs have partial information about eavesdropper's location, we
propose two transmission schemes: friendly UAV jamming (FUJ) and Gaussian
jamming transmission (GJT) for the cases when jamming signals are known and
unknown a priori at destination, respectively. Then, we formulate an average
secrecy rate maximization problem to jointly optimize the transmission power
and trajectory of UAVs, and the power splitting ratio of destination. Being
non-convex and hence difficult to solve the formulated problem, we propose a
computationally efficient iterative algorithm based on block coordinate descent
and successive convex approximation to obtain a suboptimal solution. Finally,
numerical results are provided to substantiate the effectiveness of our
proposed multiple-UAV schemes, compared to other existing benchmarks.
Specifically, we find that the FUJ demonstrates significant secrecy performance
improvement in terms of the optimal instantaneous and average secrecy rate
compared to the GJT and the conventional single-UAV counterpart.
