Abstract
The multitarget position-sensitivity security transmission scheme with orbital angular momentum (OAM) directional modulation (DM) waveform using the uniform circular frequency diverse array (FDA) is proposed. The transmitter employs FDA to generate dual-mode range-dependent OAM beam pattern, and the direction information of OAM beam is modulated into the signal. According to the modulation method, orthogonal carrier frequency can be designed to realize multitarget position-dependent OAM pattern. In the undesired position, the intensity pattern and the phase front of the radio beam vary randomly with the digital transmission sequence. Because modulation waveform is position-dependent, the technique offers security, as the signal can be purposely distorted in other positions. 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 multitarget position-sensitivity OAM-DM technology based on FDA offers the security transmission scheme.
Highlights
Wireless communication has the risk of being intercepted without physical-layer security measures [1]
As compared with phased array, frequency diverse array (FDA) can generate range-dependent beam pattern with a small frequency increment [6,7,8]. e range-dependent physical-layer security with FDA can be done in several ways [9,10,11,12,13,14,15,16,17,18]. e information code can be designed for FDA, which generates the specific radiation pattern. e transmission beam pattern is related to the range and the azimuth angle based on FDA element with the frequency increment for the directional modulation (DM) technique, in which the transmitted symbols are purposely distorted to be unrecoverable except for the legitimate user
Due to the position-dependent orbital angular momentum (OAM) beam pattern, constellations of two QPSK signals obtained by modulation and code will be distorted to varying degrees in different positions, which can interfere with the eavesdropper to get the correct information. erefore, dualmode OAM-DM signal with position-sensitivity can achieve security transmission in the desired position
Summary
Wireless communication has the risk of being intercepted without physical-layer security measures [1]. In [19], 2-bit phase control is used on a two-element FDA antenna, and the generated radiation pattern with directiondependent projects the phase modulation signal as a constellation for physical-layer security communication. The FDA generates the range-dependent OAM signal, and the confidential information is encoded on OAM modes in [37] This scheme offers only one-dimensional range-dependent security transmission, which cannot be projected to a specific position in three-dimensional space. E range, elevation, and azimuth information carried by dual OAM beams are modulated into the signal constellation to generate OAM-DM signals, which can realize specific position-sensitivity security transmission in three-dimensional space. E receiver can use a single antenna to demodulate OAM-DM signal related to specific range, elevation, and azimuth at the desired position, without requiring a large aperture array antenna to receive the complete wavefront. Two OAM-DM signals are synthesized into one signal to restore the correct digital information, which is conducive to reducing the eavesdropping risk
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