## 5 Conclusions  
In the process of performing various missions using a swarm of vehicles, the possibility of malicious attacks such as data forgery and falsification must be considered, especially in situations where accurate location estimation is required. In the UWB positioning system, data generated from each node are used to calculate the ToF. Data safety is very important because, if even a single piece of data is forged or altered, the accuracy of location measurement can be greatly reduced. Therefore, by introducing a DAG-based logical network between each node, data integrity and safety are guaranteed, and location measurement performance is prevented from deteriorating. In this paper, we proposed a safe and accurate location measurement framework using improved UWB positioning techniques and a DAG-based distributed ledger. We proposed a DS-TWR-based ranging module optimized through empirical calibration and a positioning module. which improved the existing trilateration by applying the Levenberg-Marquardt algorithm, a nonlinear least-squares optimization technique. Moreover, by applying a new consensus algorithm to the distributed ledger of the proposed localization framework, the transaction processing performance per unit time was improved, and the delay time was reduced, thereby satisfying the real-time requirements of location technology. Ultimately, we proposed a complete positioning framework that applies improved positioning techniques and distributed ledger technology and conducted various performance evaluations for each detailed technology. We demonstrated the performance of the localization system constituting our framework through experiments in a real environment and validated how the localization performance changes when the actual received data are tampered with by malicious attacks. In addition, the distributed ledger technology using a new consensus algorithm was verified in terms of threshold dependence and network scale dependence. As a result, the proposed system reduced the speed of confirmation saturation as the threshold increased, and consistent transaction processing performance can be achieved regardless of network scale. Finally, we verified the security performance of the proposed framework by measuring the average deactivation time and confirmation rate through a race attack scenario on the distributed ledger system. The proposed distributed ledger technology had a reduced average deactivation time compared to existing DAG systems and showed constant transaction processing performance regardless of malicious transaction creation. Figure 9: The result of measuring the confirmation rate according to the probability of a malicious transaction. We have several research plans for future work. First, we plan to improve the positioning performance through machine learning or a more-advanced optimization model. Second, we will apply a smart contract and off-chain solution for the efficiency and scalability of our proposal. This will allow us to improve the positioning accuracy and strengthen the decentralization of the proposed positioning framework. Conceptualization, K.K., S.L. and T.Y. ; methodology, K.K., S.L., T.Y. and H.K. ; software, K.K. and S.L. ; validation, S.L., T.Y. and H.K. ; formal analysis, S.L., T.Y. and H.K. ; investigation, K.K., S.L. and T.Y. ; resources, K.K., S.L. and T.Y. ; data curation, K.K., S.L. and T.Y. ; writing--draft preparation, K.K., S.L., T.Y. and H.K. ; writing--review and editing, K.K., S.L., T.Y. and H.K. ; visualization, K.K., S.L. and T.Y. ; supervision, H.K. ; project administration, H.K. ; funding acquisition, H.K. All authors have read and agreed to the published version of the manuscript. This work was supported through the National Research Foundation of Korea (NRF) using the financial resources granted by the Ministry of Science and ICT (MSIT) (No.