# A Physical Layer Security Enhancement Scheme under the Ambient Backscatter System
###### Abstract
[PERSON] [14] proposed an artificial noise auxiliary collaboration scheme, one of the cognitive relays that successfully decodes the source signal is selected as the relay to retransmit the secret signal, and the other relays emit artificial noise that confuses the eavesdropper but does not damage the channel quality of the legitimate receiver, so the security performance of the secondary network is enhanced. In addition, [PERSON] [15] proposed a design scheme of relay tag antenna based on the genetic algorithm in the ABC environment, which realized the directional communication from the relay tag to the legitimate receiver and enhanced the physical layer security of wireless communication. However, from the above research, we can find that the research on the physical layer security scheme of wireless communication under the ABC environment is not sufficient. What's more, in the physical security scheme using the technique of artificial noise often require one or more auxiliary relay nodes, but the security performance under this system model is highly dependent on the relay node, after the failure or damage of the relay, the system secure communication function cannot be realized, so the overall reliability of the system is poor. Even if some scheme does not depend on fixed relay, it is carried out under the condition of a fixed channel model or on the assumption that the channel state information (CSI) is known. Traditional channel estimation methods must send pilot symbols, which cannot be directly applied to the ABC system. Therefore, we proposed an enhanced communication security scheme that generates artificial noise from the tag end in the ABC environment. This scheme does not depend on key relay nodes, so the reliability of the system can be improved. In the IANT scheme, there are K tags to communicate with a legitimate reader, and there are eavesdropping devices to monitor the communication signal. In the RFID environment, the conventional method to improve the physical layer security is to inject noise from the reader end, and then send the signal with noise to the tag. After the reader receives the backscatter signal of the tag, it uses its own noise to remove the noise. In the ABC environment, the reader does not supply energy for tags, so in our scheme, we choose two tags to send signals to the reader at the same time, one to send tag data and the other to generate artificial noise. The symmetry of the content studied in this paper is reflected in the reception of the signal. There are reader, eavesdropper, and passive tags in the system model of this paper. due to the broadcast characteristics of the wireless channel, the signal backscattered by the tag will reach the reader and the eavesdropper at the same time, i.e., the signals they receive are symmetrical. What we have done is to make the reception effect of the reader different from that of the eavesdropper under this condition. The main contributions we made in this paper are as follows:  
* In the ABC environment, we proposed a scheme IANT that uses physical layer strategies to enhance system security. As far as we know, it is the first time to study the physical layer security scheme from the perspective of artificial noise in thje ABC environment system. * Different from previous studies, in order to better adapt to the ABC environment, a new method is adopted to dynamically estimate channel parameters, which does not need pilot symbols. * Compared with the contrast scheme, the IANT scheme achieves a secrecy rate that is approximately twice the contrast scheme under the condition that the bit error rate (BER) is slightly reduced, which effectively enhances the security performance.