  Communication in the millimeter-wave (mmWave) band has recently been proposed
to enable giga-bit-per-second data rates for next generation wireless systems.
Physical layer security techniques have emerged as a simple and yet effective
way to safeguard these systems against eavesdropping attacks. These techniques
make use of the large antenna arrays available in mmWave systems to provide an
array gain at the target receiver and degrade the signal quality at the
eavesdropper. Despite their effectiveness, majority of these techniques are
based on line-of-sight communication links between the transmitter and the
receiver, and may fail in the presence of blockages or non-line-of-sight links.
This paper builds upon previous work and extends physical layer security to the
non-line-of-sight communication case and randomly located eavesdroppers.
Specifically, the large dimensional antenna arrays in mmWave systems and the
intrinsic characteristics of wireless channel are exploited to induce noiselike
signals that jam eavesdroppers with sensitive receivers. Numerical results show
that the proposed techniques provide higher secrecy rate when compared to
conventional array and physical layer techniques based on line-of-sight links.
