Research on Physical Layer Security Scheme Based on OAM Modulation for Wireless Communications

Aiming at the physical layer information security risk in wireless communication system, a physical layer security transmission technology based on OAM (Orbital angular momentum) modulation is proposed in this paper. Through introducing the OAM state as an information bearing parameter, the modulated electromagnetic (EM) wave will have a helical transverse phase structure, which means that the phase front varies linearly with azimuthal angle. In such case, the modulated signal will present the direction-dependent characteristic; in addition, since the OAM state becomes very weak beyond a certain distance, utilizing this characteristic, the effective communication distance can be limited. Therefore, the communication range can be accurately limited by OAM modulation. Furthermore, an OAM pre-compensation algorithm is proposed to improve the QoS of legitimate users. The simulation results show that the proposed scheme can effectively prevent eavesdroppers from detecting OAM modulated signals.