## 2 Related Work
### DAG-Based Distributed Ledger  
DAG generally refers to a directed acyclic graph data structure, but in the blockchain industry, it is commonly used as a term for distributed ledger technology utilizing the DAG structure [39; 40]. DAG-based distributed ledger technology is used to implement a distributed system to process and store data transactions [41]. In a DAG-based distributed ledger system, all transactions are connected simultaneously and in parallel in the form of a directed graph. Since the DAG structure itself, where transactions are connected, acts as a kind of chain, a distributed ledger can be implemented by eliminating the blocks of the existing blockchain system and leaving only the chain format [42].  
Blockchain-based distributed ledgers have scalability problems when applied to IoT-based networking systems that handle many data because they require complex verification and block creation for transaction processing [43; 44]. Additionally, considering the limited computing power on vehicle networks using low-power devices such as UAVs, high latency may occur, which may not be helpful in applying distributed ledger technology in real scenarios. Therefore, we intended to solve the existing problems by facilitating data processing on vehicle networks using DAG-based distributed ledger technology.  
The following are ongoing studies involving DAG-based distributed ledger systems. A study was conducted comparing the differences between blockchain and DAG-based distributed ledger structures. Research has been progressed to analyze various DAG-based commercial blockchain technologies [45]. Additionally, extensive research has been conducted to apply DAG-based distributed ledger technology to IoT networks in various fields such as smart grids [46], industrial IoT [47], the 6G network [48], energy trading [49], and smart communities [50]. Furthermore, studies related to advanced DAG-based distributed ledger systems are emerging, such as considering the efficient consensus process of DAG-based distributed ledger technology [51], flexibly adapting to transaction demands [52], and developing a private distributed ledger system [53]. Lastly, research has also progressed on the security of DAG-based distributed ledgers, such as resilience in IoT applications [54] and the stability of unverified transactions [55].  
In summary, many studies have been conducted to apply DAG-based distributed ledger technology in various fields. In addition, using DAG-based distributed ledger technology has advantages in terms of transaction processing time and computing power compared to existing blockchain-based systems. Therefore, we introduced DAG-based distributed ledger technology into a localization system composed of multiple IoT devices. This approach promotes the parallel processing of data in the localization network, ensuring fast transaction processing and solving existing scalability problems. Moreover, the proposed system can prevent data forgery and falsification through transparent processing of localization data transactions. Consequently, our design enables secure data transmission and storage in a localization system where each node collects and processes the positioning information of its neighbors.