*Article* **Secure Transmission of Terahertz Signals with Multiple Eavesdroppers**

**Yuqian He 1, Lu Zhang 1, Shanyun Liu 2, Hongqi Zhang <sup>1</sup> and Xianbin Yu 1,2,\***


**Abstract:** The terahertz (THz) band is expected to become a key technology to meet the everincreasing traffic demand for future 6G wireless communications, and a lot of efforts have been paid to develop its capacity. However, few studies have been concerned with the transmission security of such ultra-high-speed THz wireless links. In this paper, we comprehensively investigate the physical layer security (PLS) of a THz communication system in the presence of multiple eavesdroppers and beam scattering. The method of moments (MoM) was adopted so that the eavesdroppers' channel influenced by the PEC can be characterized. To establish a secure link, the traditional beamforming and artificial noise (AN) beamforming were considered as transmission schemes for comparison. For both schemes, we analyzed their secrecy transmission probability (STP) and ergodic secrecy capacity (ESC) in non-colluding and colluding cases, respectively. Numerical results show that eavesdroppers can indeed degrade the secrecy performance by changing the size or the location of the PEC, while the AN beamforming technique can be an effective candidate to counterbalance this adverse effect.

**Keywords:** THz communications; physical layer security; multiple eavesdroppers; beam scattering; artificial noise
