# Security Performance Analysis of Full-Duplex UAV Assisted Relay System Based on SWIPT Technology
## 1 Introduction  
In recent years, UAVs have been widely used in the military, agriculture, monitoring and prediction, transportation and logistics, and disaster rescue [1; 2; 3; 4; 5] because of their advantages, such as high mobility and low-cost networking. UAV signal transmission has line-of-sight link transmission and broadcasting characteristics, which will make the UAV communication system easier to eavesdrop on, therefore, how to guarantee the security of signal transmission has gradually become a hot issue in the study of UAV communication [6]. Compared to traditional network layer encryption techniques, physical layer security techniques have attracted a lot of attention in the field of wireless communications because they reduce the high complexity of the system and solve the problem of limited resources [7]. The combination of UAV communication and physical layer security techniques has led to a wider field of research, while UAUs play more roles in the application process. In literature [8], UAU acts as a receiver to receive signals in the presence of randomly distributed eavesdropper scenarios. In the literature [9], the UAV is used as a transmitter, and the proposed algorithm shows better convergence speed as well as good throughput by optimizing the UAV trajectory design scheme. In literature [10], the UAV acts as a jammer, moves along with the eavesdropper, and transmits a jamming signal to the eavesdropper when it reaches the optimal position, ensuring the reachable security rate of the system by reducing the eavesdropping channel capacity. It is also possible to combine multiple uses of UAVs in the design of communication systems. For example, in the literature [11], the UAV acts as both a jammer and a transmitter, sending signals to the base station while sending jamming to the eavesdropper, maximizing the Expected Sum Rate (ESR) by optimizing the position and target rate of the UAV. When the UAV works in full-duplex mode, it can act as a transmitter and a receiver at the same time [12; 13; 14], which can effectively improve the spectral efficiency of the communication system. In the literature [12], the authors combine the full-duplex technique with Reconfigurable Intelligent Surface (RIS) technique and propose a joint optimization algorithm, which improves the overall secrecy rate of the UAV system. Literature [13] introduces Non-Orthogonal Multiple Access (NOMA) technique and Idle Energy Access Point (EAP) and constructs a full duplex UAV relay system. The proposed model and strategy outperform the traditional maximum-minimum relay selection scheme in terms of throughput gain. The literature [14] considers Artificial Noise (AN)-enhanced covert wireless communication in UAV networks. In the article, the UAV uses a full duplex mode of operation and sends interference to the monitor while receiving signals, and the results show that the proposed scheme significantly enhances the covert transmission performance of the system compared to the interference-free scheme. Since the small size of the UAV leads to less energy storage, the energy limitation problem of the UAV has also attracted extensive attention from scholars. SWIPT technology was first proposed by [PERSON] in 2008 [15], which is a combination of signaling and energy harvesting technologies to draw energy from the received radio frequency (RF) signals. This technique is widely used in communication systems [16] and has been applied in UAV communication systems to alleviate the energy constraints of UAVs. Based on SWIPT technology and noise interference technology in the literature [17], the authors propose a new UAV-assisted relay security transmission protocol, and compared with the traditional terrestrial relay transmission protocol, the proposed protocol enhances the security performance of the system.