Frequency Diversity for Ultra-Reliable and Secure Communications in Sub-THz Two-Ray Scenarios

Ensuring a reliable and simultaneously secure transmission of data is one of the major challenges for wireless communication systems. This is especially difficult when no perfect channel state information (CSI) at the transmitter is available. In this work, we consider a two-ray ground reflection scenario with a passive eavesdropper. At the transmitter, there only exists limited knowledge about the channels to both the legitimate receiver and the eavesdropper. We propose a simple frequency diversity scheme which maximizes the worst-case secrecy capacity for the considered scenario. In particular, we show how to optimally adjust the frequency spacing between the used frequencies. Thereby, we can guarantee a certain secrecy rate at which data can be transmitted both reliably and securely for all locations of the receivers.