Physical Layer Secure Transmission for Multiuser Scenarios Using 4-D Antenna Arrays With Pseudorandom Time Modulation

The increasing integration of sixth-generation (6G) wireless networks with critical infrastructures requires a heightened focus on enhancing transmission security. In recent years, there has been extensive research on physical layer security (PLS) as a potential alternative to conventional security methods that rely on network complexity. The fundamental concept of PLS is to maximize the randomness of undesired channels. The high design degrees of freedom (DoFs) provided by 4-D antenna arrays make them an excellent platform for achieving secure transmission at the physical layer. However, due to the limited DoFs of time modulation, it is often challenging to balance transmission security and the number of legitimate users. The multiuser scenarios have a broader scope in practical applications. Therefore, the scalability challenges in accommodating multiple users significantly restrict the utilization of 4-D antenna arrays in PLS transmission. To address this issue, this article proposes a multiuser secure transmission approach based on 4-D antenna arrays. This approach combines baseband and time modulation, enabling simultaneous multiuser secure transmission through pseudorandom time modulation (PRTM). Some selected numerical and experimental results are also provided to validate the effectiveness of the proposed approach.