## 1 Introduction
When positioning data (in our case, the transmitting device ID for the received signal and the device timestamp data at the time of signal reception) are forged or altered due to a malicious attack on mission performance, the overall performance of the positioning system is greatly reduced, and the mission success rate is also significantly reduced. So, we propose a localization framework applying a Directed-Acyclic-Graph (DAG)-based distributed ledger to build a positioning system that not only securely processes and manages the sensor data generated from the positioning nodes, but also guarantees deterministic performance without degradation, depending on the network scale. Most distributed ledger systems applied to IoT networks, such as positioning systems, are based on blockchain and, in many cases, adopt the Proof-of-Work (PoW) as the consensus algorithm [19]. This method basically performs a hashing operation with a nonce value as the input to create a block, so it requires high computing power and causes significant delay due to the complex verification method. Moreover, the data handled in the positioning system comprise a micro-transaction with a simple structure. However, the unique nature of blockchain, which requires block generation, makes it difficult to create micro-transactions in the positioning system [20]. Our proposal adopts a DAG-based distributed ledger technology. Compared to blockchain, it has a relatively simple verification method and does not require a separate hashing operation to process the transactions, resulting in high processing speed. Additionally, it is more suitable for handling micro-transactions because it processes and manages each transaction as an individual task. Moreover, due to the nature of DAG technology, the processing speed increases as the number of participating nodes increases. This fact can give our proposal many advantages in solving scalability problems in large-scale network environments such as smart cities, smart grids, and vehicular networks [21]. Since positioning systems are mainly used for tracking or monitoring purposes, high real-time performance is required. These systems are inevitably sensitive to latency. Even with DAG-based technology, the delay time and workload that occur in the process of creating, verifying, and confirming transactions and synchronizing transaction information cannot be ignored [22]. For these reasons, we propose a new consensus algorithm suitable for the positioning environment to reduce the delay time that occurs in the ledger layer during the positioning process and improve the transaction processing speed. It is a global state consensus based on a threshold and proposes a method to quickly confirm micro-transactions for positioning. Based on the descriptions so far about using distributed ledger technology in a localization environment, the contributions of this article are summarized as follows:  
* Distance-based positioning methods that use multiple distance values and the fixed coordinates of anchors have default errors and serious distortion problems in noisy environments. To solve this, we propose an enhanced localization technique using a nonlinear least-squares optimization technique and verified its performance. * We propose a new consensus algorithm applicable to DAG-based distributed ledgers and suitable for positioning systems. Due to the nature of existing DAG-based distributed ledgers, individual nodes manage their own local state, which can cause excessive computing load and delay the time to reach consensus. We applied a new consensus algorithm to improve the efficiency during the consensus-reaching process and describe in detail how to apply it in the target environment. * We designed a complete localization framework with a DAG-based distributed ledger equipped with the proposed localization technology and consensus algorithm. Through this, we systematized and concretized our suggestions.