Signal Domain Multi-Component Based Secure Hybrid Precoding for mm Wave Systems

In this paper, we investigate hybrid precoder design to enhance the physical layer security of millimeter-wave (mmWave) multiple-input single-output (MISO) systems with sub array structure. Addressing the power wastage issue in artificial noise (AN)-based schemes, we introduced an extra signal domain dimension and proposed a signal domain multi-component based secure hybrid precoding model. The proposed model joints signal and spatial domains for the design of baseband and analog precoders, ensuring that the received signal at the legitimate user satisfies specific signal domain characteristics. As a result, all received energy at the legitimate user can be used for signal recovery, while the distorted signal at eavesdroppers inevitably forms inter-component interference. Moreover, by introducing general multi-fractional Fourier transform (GMFRFT) signal domain into the model, a specific GMFRFT-based scheme is proposed and the secrecy performance is analyzed in detail. Furthermore, to better utilize spatial domain resources, a GMFRFT-based scheme with dynamic subarrays is proposed, along with a low-complexity subarray partitioning algorithm. Numerical results demonstrate the advantages of the proposed schemes over existing schemes.