Position‐sensitivity security transmission with orbital angular momentum directional modulation based on frequency diverse array

Abstract

The position-sensitivity security communication scheme with orbital angular momentum (OAM) directional modulation (DM) beam pattern generated by the uniform circular frequency diverse array (FDA) is proposed. The transmitter employs FDA antennas to generate dual-mode range-dependent OAM beam and the direction information of OAM beam is modulated into the signal. The designed signal with random frequency offset excites the element of the uniform circular FDA to generate orthogonal OAM signals in the desired position. In the undesired position, the intensity pattern and the phase front of the radio beam vary randomly with the digital sequence transmission, which can make eavesdropping difficult. Since the modulation waveform has position-dependent, the signal can be purposely distorted in undesired positions to provide transmission security for the legitimate user. The composite dual-mode OAM signal makes it more difficult for eavesdroppers to demodulate correct messages. The receiver with a single antenna employs the phase compensation and helical phase factor to restore the correct digital signal in the desired position. Numerical results show that the space position-sensitivity OAM-DM technology based on FDA offers a security transmission scheme.