Secrecy Zone Achieved by Directional Modulation with Random Frequency Diverse Array

This work analyzes the impact of the transceivers' relative locations on the physical layer security achieved by directional modulation with a random frequency diverse array (DM-RFDA). Based on the adopted path loss model, we first derive the probability of non-zero secrecy capacity, denoted by p_n, achieved at a legitimate receiver for an eavesdropper with a fixed location. We then examine how far we need to push the eavesdropper away from the transmitter in order to guarantee p_n \geq \delta, where \delta is a given value determining a certain level of security. The results reveal that the DM-RFDA system ensures a high level of security (e.g., \delta = 0.95) for the legitimate user who is significantly further away from the transmitter than the eavesdropper. Furthermore, the results demonstrate that it is easier to guarantee the required level of security when there are more resource (e.g., higher bandwidth and a larger number of transmit antennas) in the DM-RFDA system.