  Device-to-device (D2D) communication raises new transmission secrecy
protection challenges, since conventional physical layer security approaches,
such as multiple antennas and cooperation techniques, are invalid due to its
resource/size constraints. The full-duplex (FD) jamming receiver, which
radiates jamming signals to confuse eavesdroppers when receiving the desired
signal simultaneously, is a promising candidate. Unlike existing endeavors that
assume the FD jamming receiver always improves the secrecy performance compared
with the half-duplex (HD) receiver, we show that this assumption highly depends
on the instantaneous residual self-interference cancellation level and may be
invalid. We propose an adaptive jamming receiver operating in a switched FD/HD
mode for a D2D link in random networks. Subject to the secrecy outage
probability constraint, we optimize the transceiver parameters, such as
signal/jamming powers, secrecy rates and mode switch criteria, to maximize the
secrecy throughput. Most of the optimization operations are taken off-line and
only very limited on-line calculations are required to make the scheme with low
complexity. Furthermore, some interesting insights are provided, such as the
secrecy throughput is a quasi-concave function. Numerical results are
demonstrated to verify our theoretical findings, and to show its superiority
compared with the receiver operating in the FD or HD mode only.
