## 1 Introduction
Inspired by the multiple antenna arrays idea presented in [40; 41; 42], we are dedicated to achieving secure and precise DM transmissions based on a multiple antenna arrays model for the purpose of addressing the neighbor security issue that exists in traditional DM schemes. This is the main motivation and goal of our paper. Overall, the main novelties and contributions of our work can be summarized as follows. (1) A multiple antenna arrays model combined with AN technique is introduced into DM designs to settle the neighbor security problem in traditional single antenna array based DM schemes for PLS enhancement. (2) Due to the introduction of the multiple antenna arrays model, the useful signals are mixed together at the receiver side. To recover the intact useful signals, two secure and precise DM transmission schemes based on single- and multi-carrier multiple antenna arrays model are proposed, respectively. For each scheme, the architectures of the transmitter and the legitimate receiver are elaborately designed, individually. In single-carrier DM scheme, the receive multi-beamforming method is adopted at the receiver side. In multi-carrier DM scheme, the multi-carrier method is utilized at the transmitter side, and the mixed useful signals can be easily recovered by using multiple band-pass filters at the receiver side. (3) Three important metrics for the proposed DM schemes, namely the symbol error rate (SER), secrecy rate, and robustness, were deduced and verified with simulations. The comparisons among the proposed DM schemes and the traditional AN-aided single antenna array DM schemes were also performed. The proposed schemes can be typically applied to the future LOS communication environments. Their major application scenarios include secure military communications, satellite communications, unmanned aerial vehicle (UAV) networks, Internet of Things (IoT), and millimeter communications [43]. The remaining part of the paper is organized as follows. The principle of multiple antenna arrays based DM transmission is briefly introduced in Section 2. Sections 3 and 4 illustrate the principles of the proposed DM schemes based on single-carrier multiple antenna arrays model and multi-carrier multiple antenna arrays model, respectively. Section 5 presents the SER, secrecy rate,and the robustness performance of the proposed DM schemes, and further compares the proposed DM schemes with the traditional AN-aided single antenna array DM schemes. Then, performance simulations and discussions are shown in Section 6. Section 7 concludes this paper and points out the future research directions. Throughout this paper, boldface uppercase, boldface lowercase, and lowercase letters are used for matrices, vectors, and scalars, respectively. The superscripts \((\cdot)^{*}\), \((\cdot)^{T}\), \((\cdot)^{H}\), and \((\cdot)^{-1}\) denote complex conjugate, transpose, complex conjugate transpose, and inverse operators, respectively. The function \(\mathrm{card}(\cdot)\) represents the cardinality of a set. The operator \(\mathbb{E}(\cdot)\) means the statistical expectation. The sign \(|\cdot|\) denotes the absolute value of a scalar. The notation \([\cdot]^{\dagger}\) refers to \(\max\{0,\cdot\}\). \(\mathbf{0}\) is the all zero vector, \(\mathbb{R}\) is the set of all real numbers, and \(\mathbb{C}\) is the set of all complex numbers. \(\mathbf{I}_{N}\) represents an \(N\times N\) identity matrix. The expression \(x\sim\mathcal{CN}(0,\sigma^{2})\) means that random variable \(x\) obeys a circularly symmetric complex Gaussian (normal) distribution with zero mean and variance \(\sigma^{2}\). The abbreviations \"Tx\", \"mc\", \"sc\", \"sa\" in the figures of this paper refer to the symbol stream transmitted by transmitter, the multi-carrier multiple antenna arrays DM scheme, the single-carrier multiple antenna arrays DM scheme, and the single antenna array DM scheme, respectively.