Wireless Secure Communication Links Established by Diverse Code-Frequency Joint Modulated Metasurfaces

The rapid evolution of the Internet of Things (IoT) and fifth-generation (5G) and beyond telecom networks has led to an increased importance of wireless secure communication. A significant advancement in secure communication has recently been achieved by space–time modulated metasurfaces, which exploits the spatial and frequency degrees of freedom in a metasurface to distinguish between users and potential eavesdroppers. Here, besides the already utilized spatial and frequency domains, we add the use of the code domain. The concept of diverse code-frequency joint modulated metasurfaces (DCF-JMM) is proposed, and point-to-point secure links are realized that can distinguish multiple users located along the same direction (or even at the same position) and provide robust safeguards against eavesdropping and jamming. To demonstrate the approach, a DCF-JMM with three partitions is implemented and used to simultaneously transmit three letters to three or two users, illustrating the flexibility and efficiency of the proposed technique. The proposed scheme has the potential to expand the communication capacities of wireless systems, opening new possibilities for next-generation wireless networks.