Energy Efficiency Optimization Based Directional Modulation for Security Communications

Conventional Directional Modulation (DM) can produce phase disturbances in the direction of the eavesdropper to enhance communication security. However, it does not take into account the benefits to security that arise from the signal-to-noise ratio (SNR) of the received signal, nor does it consider the energy efficiency of the transmitted signal, resulting in a high security energy consumption. This paper proposes an optimization objective based on the concept of secrecy information rate, that comprehensively considers the energy of the received signal by legitimate user and the distortion of constellation points by the eavesdropper. The improved DM accounts for environmental noise and signal attenuation over distance, as well as the influence of interfering signal phases in the eavesdropping direction on secure communication performance. Finally, it provides a relationship curve between the optimized secure capacity and energy efficiency, which is beneficial for better balancing secure communication requirements in terms of distance and angle in practical scenarios.