## 1 Introduction  
Wireless communication systems based on mmWave massive hybrid arrays offer higher network security, as the line-of-sight transmission and high directionality of the mmWave create a wired-like environment, while array antenna systems provide greater flexibility for physical layer network security technologies. Through the appropriate configuration and the use of beamforming technologies, users and intruders can receive entirely different signals. This approach can even achieve physical layer security without any prior knowledge of intruder information. For single-user access, transmission security depends on the magnitude of the sidelobe beams. In the case of multi-user spatial division access, where multiple beams are used simultaneously, the magnitude of the sidelobebeams becomes more challenging to characterize, making the description of the secure capacity extremely complex. Beamforming is primarily carried out from two aspects: one is the design based on secrecy capacity, which ensures that system communication efficiency is maximized under the condition that eavesdroppers cannot intercept, with the main goal being to maximize the secrecy rate during communication; the other is the design based on SNR, which aims to weaken the eavesdropper's interception capability as much as possible while ensuring the normal communication efficiency of the main channel. The authors of [1] design a low-complexity beamforming scheme in reconfigurable intelligent surface (RIS)-assisted communication systems to enhance physical layer security. The security performance of quasi-orthogonal space-time block codes with power scaling in MIMO Rayleigh fading eavesdropping channels is investigated in [2]. By employing moment matching approximation technology, a closed-form approximation of the secrecy outage probability is derived. As a commonly used auxiliary method, artificial noise (AN) is often combined with beamforming to implement secure transmission strategies. The channel covariance matrix is used for beam design in [3]. By performing eigenvalue decomposition on the channel covariance matrix, beam domain information is obtained, which serves as the basis for jointly optimizing beam selection and artificial noise power allocation. The optimization problem of eavesdropping prevention and the main lobe bit error rate (BER) under the constrained AN power is investigated in [4]. The spatial and frequency domains are combined in [5] and redundant AN is introduced to interfere with the eavesdropper. Under the condition where only the statistical channel state information (CSI) of the legitimate user and the eavesdropper is available, an AN-aided transmission strategy can be used to enhance the security of single-cell massive MIMO systems [6]. Moreover, beamforming technology can also be applied to multi-user systems. An RIS-assisted multi-user massive MIMO system is considered in [7], utilizing AN for secure communication. The system's secrecy rate in spatially correlated channels is derived, and the power allocation of AN and phase shifts of the RIS are further optimized. In [8], a transmission method combining space-time line coding and AN is proposed for the multi-user MIMO downlink, and the lower bound of the secrecy sum rate is derived. For the downlink multi-user generalized spatial modulation system, block diagonalization is first employed to eliminate inter-user interference and then AN is used to prevent eavesdropping [9]. Similarly, in the context of multi-user interference, a more powerful eavesdropper with more antennas than the legitimate users is considered in [10]. User utility is defined as the secrecy rate minus the inter-user interference, and the study focuses on optimizing the total utility of all users. On the other hand, security schemes based on the GSVD have also garnered widespread attention in communications. Employing a GSVD-based beamforming scheme and allocating corresponding transmission power to spatial streams can optimize the secrecy rate [11; 12].