# Cooperative Friendly Jamming Techniques for Drone-Based Mobile Secure Zone
## 2 Related Work
### Friendly Jamming Security Model for Mobility Environment  
Research is underway for friendly jamming security models using multiple unmanned aerial vehicles (UAVs) in mobile communication networks. The Friendly UAV Jamming (Fri-U) method has shown that the eavesdropping probability decreases as the number of jammers deployed near the protection zone increases because the signal to interference and noise ratio (SINR) of the eavesdropping device drops through the transmitted signals of the jammers [19]. In addition, there is a study that proved its effectiveness by applying Fri-U) to IoT technology in the medical field [20]. However, using the Fri-U), as the number of UAVs increases, the number of jammers increases, thereby increasing the loss cost, and in practice, making it difficult to install an infinite number of jammers. Therefore, research is required to compare, analyze, and propose an effective friendly jamming model in a mobile communication environment based on the size of the secure zone, the number of jammers, and the security efficiency relative to cost.  
In addition, research on location optimization considering the mobility of UAVs is being conducted. The location of the drone is important in order to reduce the waiting time and delay of the user or improve the quality of the service provided to users [21]. In [22], the disturbance power intensity and power trajectory path that occur when protecting legitimate nodes located on the ground using friendly jamming signals were studied. At that time, it was calculated by estimating the location of the eavesdropper, but the applicability is low because it is difficult to determine the location of the eavesdropper in the actual situations. Accordingly, in [23], randomness was modeled without identifying the location of the eavesdropper. At that time, in order to maximize the secret ratio of several legitimate receivers, the area was determined using the signal-to-noise ratio (SNR). However, as the confidentiality of the receiver in the security area is not guaranteed equally, some devices have a high potential for eavesdropping. In addition, when the optimal location is determined, only some factors change depending on the situation, so the area is not flexible and the mobility of UAVs cannot be utilized. In the case of battery usage, it is inefficient because jamming signals must be transmitted all the time.  
Table 1 shows a summary of prior studies related to friendly jamming. In the table header, \"Paper Title\" refers to the title of the study, and \"Research Topic\" refers to the keywords of the study. \"Number of Jammers\" refers to the number of jammers used in the model: Here, \"single\" indicates that the model used one jammer, and \"multiple\" indicates that the model used two or more jammers. In addition, \"Main Idea\" refers to the model proposed in each paper, and \"Limitation\" refers to those analysis results that are a limitation of the indicated study. The models in the prior studies are inefficient and inflexible in terms of creating a secure zone for secure wireless communication because they consume large  
amounts of power and have no mobility. In this study, however, we proposed a model that creates an efficient and flexible secure zone by using only three drones that transmit friendly jamming signals, and we demonstrated the effectiveness of the model through simulations and field experiments.