The Research Of Directional-Modulation Physical-Layer Security Communication System Basing Phase-Modulation Surface

Physical-layer security is to ensure the safety of wireless communication by designing the self-characteristics of wireless communication system,such as the coding scheme,modulation and transmission mode.As the supplement of conventional encryption protocols,the research of physical-layer security contributes to dealing with the challenges the conventional encryption methods faces.To improve the security of wireless signal while transmits in the physical layer,a new directional data encrypt communication system using phase-modulation surface with tuneable electromagnetic scattering characteristics is proposed in this paper.The scattering characteristic of phase-modulation surface is researched firstly.The electronic control scheme of the active frequency-selective surface in phase-modulation surface is optimized by differential evolution algorithm to improve its microwave absorbing property.Based on its tuneable scattering characteristics,the phase-modulation surface is used as the reflector in the constructure of a reflector antenna in this paper.The reflecting states of active surfaces in phase-modulaton surface are switched between strong reflection and weak reflection with the frequency higher than the bit rate of excitation signal,which means the excitation signal is spatial sampled by phase-modulation surface in the period of code-width.The constellation diagram of the signal transmitted in this way is diverse while received at different spatial positions.The communication information can only be demodulated at a specific receving angle and the constellation diagrams of receving signal at other angles all distort,therefore,preventing the information being stolen.Furthermore,the bandwidth of transmitted signal is extended so highly that its spectrum is buried in the noise.So it is difficult for the enemy to detect the communication process and transmit the interfering signal accurately to block the normal communication.Simulation results show the transmitted directional data encryption signal in the proposed communition system has the properties of low probability of detection,low probability of interception,anti-jamming and the ability to combat the channel attenuation,therefore,improves the security of wireless signal while transmitting in the phyaical layer.