Aiming at the problem that the traditional classification and recognition scheme has few effective features and low recognition accuracy in the process of UAV acoustic signal recognition, a new method based on Gramian Angular Field (GAF) and Convolutional Neural Network (CNN) is proposed. Using the methods of Gramian Angular Summation Field (GASF) and Gramian Angular Difference Field (GADF), one-dimensional UAV acoustic signals are mapped into two-dimensional images. Then, a convolutional neural network model suitable for UAV acoustic signal classification is designed, and the two-dimensional image is used as input, thereby realizing UAV acoustic signal recognition. The experimental results show that compared with the GASF algorithm, the GADF algorithm has higher recognition accuracy and better reliability. The GAF algorithm has more significant features of the UAV acoustic signal than the traditional feature extraction algorithm, and is more suitable for using convolutional neural network for recognition. Compared with other UAV acoustic signal recognition schemes, the GAF combined with CNN method designed in this paper has better performance.
With the rapid development of mobile Internet technology and the continuous improvement of people's understanding of data security, the research on the secure transmission of information in wireless communication systems has received extensive attention. Using physical layer security technology to protect the information transmission security is not only beneficial to prevent illegal eavesdroppers from obtaining the transmitted information, but also greatly reduces the computational complexity caused by traditional encryption methods. Based on Shannon's communication theory and Wyner's wiretapping channel, this paper briefly introduces the physical layer transmission security technologies such as beamforming, artificial noise and cooperative communication, mainly analyzes massive MIMO antennas and intelligent reflecting surface, and makes a prospect summary. At the end of the paper, the open issues are identified as our future research directions.
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