  Physical-layer security (PLS) for industrial indoor terahertz (THz) wireless
communication applications is considered. We use a similar model as being
employed for additive white Gaussian noise (AWGN) wireless communication
channels. A cell communication and a directed communication scenario are
analyzed to illustrate the achievable semantic security guarantees for a
wiretap channel with finite-blocklength THz-wireless communication links. We
show that weakly directed transmitter (Alice) antennas, which allow cell-type
communication with multiple legitimate receivers (Bobs) without adaptation of
the alignment, result in large insecure regions. In the directed communication
scenario, the resulting insecure regions are shown to cover a large volume of
the indoor environment only if the distance between Alice and Bob is large.
Thus, our results for the two selected scenarios reveal that there is a
stringent trade-off between the targeted semantic security level and the number
of reliably and securely accessible legitimate receivers. Furthermore, the
effects of secrecy code parameters and antenna properties on the achievable
semantic security levels are illustrated to show directions for possible
improvements to guarantee practically-acceptable security levels with PLS
methods for industrial indoor THz-wireless communication applications.
