  We aim to secure a large-scale device-to-device (D2D) network against
adversaries. The D2D network underlays a downlink cellular network to reuse the
cellular spectrum and is enabled for simultaneous wireless information and
power transfer (SWIPT). In the D2D network, the transmitters communicate with
the receivers, and the receivers extract information and energy from their
received radio-frequency (RF) signals. In the meantime, the adversaries aim to
detect the D2D transmission. The D2D network applies power control and
leverages the cellular signal to achieve covert communication (i.e., hide the
presence of transmissions) so as to defend against the adversaries. We model
the interaction between the D2D network and adversaries by using a two-stage
Stackelberg game. Therein, the adversaries are the followers minimizing their
detection errors at the lower stage and the D2D network is the leader
maximizing its network utility constrained by the communication covertness and
power outage at the upper stage. Both power splitting (PS)-based and time
switch (TS)-based SWIPT schemes are explored. We characterize the spatial
configuration of the large-scale D2D network, adversaries, and cellular network
by stochastic geometry. We analyze the adversary's detection error minimization
problem and adopt the Rosenbrock method to solve it, where the obtained
solution is the best response from the lower stage. Taking into account the
best response from the lower stage, we develop a bi-level algorithm to solve
the D2D network's constrained network utility maximization problem and obtain
the Stackelberg equilibrium. We present numerical results to reveal interesting
insights.
