# A Physical Layer Security Enhancement Scheme under the Ambient Backscatter System
###### Abstract  
In this paper, we proposed a scheme that Injects artificial noise from the tag end (IANT) to enhance the physical layer security of the ambient backscatter communication (ABC) system. The difference between the ABC system and the traditional radio frequency identification system is whether it uses the radio frequency (RF) signals in the environment to supply energy and modulation information for passive tags. In the IANT scheme, we select the best tag to communicate with the reader according to the channel quality between tags and reader, and at the same time select another tag to generate artificial noise that affects the receiving effect of the eavesdropper. This paper uses the method of generating noise copies in the reader to reduce the interference of artificial noise on the signal received by the reader. The simulation results show that with the increase in channel quality between tags and reader and the increase in the number of tags, the proposed IANT scheme is significantly superior to the contrast scheme in terms of system achievable secrecy rate, effectively enhancing the physical layer security of the ABC system. physical layer security; passive tags; artificial noise; ambient backscatter communication +
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Footnote †: journal: **Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. But there are still some challenges. The broadcast nature of wireless signals makes it easy for some eavesdroppers to get the information content. Traditional secure encryption algorithms are not suitable for Internet of Things devices with limited computing power and energy. In this context, the research on physical layer security technology has become a new idea to guarantee communication confidentiality. The basic principle of physical layer security is to use noise and the inherent randomness of the channel to limit the information extracted from the received signal by the illegal receiver. [PERSON] [8] characterized the secrecy of the RFID backscattering system. Then, a new method is proposed to maximize the confidentiality by making use of the properties and characteristics of the RFID backscattering channel. [PERSON] [9] not only injects noise from the reader but also uses a one-dimensional antenna array to deploy beam steering on the tag side, which effectively protects the information of the RFID tag from eavesdroppers. [PERSON] [10] researched the problem of secure communication between two legal nodes in the case of eavesdropping nodes in the wireless channel. The transmitter uses a part of the power to generate artificial noise to ensure the confidentiality of the communication process, which only reducing the channel quality of eavesdropping nodes. [PERSON] [11] researched an eavesdropping channel with an auxiliary scrambler. In the presence of an eavesdropper, the transmitter, with the help of an independent scrambler, communicates confidentially with its legal receiver. In discrete memory-less channel and Gaussian channel, respectively, the realized security rate is obtained. [PERSON] [12] proposed a user scheduling scheme based on multi-user diversity gain. A single user is scheduled for data transmission, and a number of other users generate independent artificial noise, so as to conduct confidential communication between the scheduling user and the legitimate receiver against the eavesdropper. [PERSON] [13] proposed a user-relay collaborative selection scheme and determined the optimal power allocation between the data signal and the artificial noise at the transmitter on the basis of minimizing the probability of secrecy interruption, so as to improve the physical layer security in the multi-user multi-relay network.