# Timing Performance Testing and Regularity Analysis of eLoran System
## 1 Introduction  
As modern communication, navigation, and scientific research continue to evolve, the importance of time synchronisation is becoming increasingly apparent. Time is a critical resource for various applications, ranging from network communications and precise scientific experiments to financial transactions [1]. Accurate time synchronisation improves system performance and efficiency while supporting a range of complex applications, including precision navigation, astronomical observation, seismic monitoring, and satellite communications [2, 3].  
In the field of time synchronisation, accurate timing is essential for several critical applications, particularly in communication, navigation, and scientific research. Time synchronisation plays a vital role in ensuring the accuracy of financial transactions in banks and in maintaining target tracking in precise missile positioning systems [4].  
As one of the most effective backups for global navigation satellite systems (GNSSs), the eLoran system primarily transmits signals via ground waves. This system features high signal transmission power, long transmission distance, and strong anti-jamming capabilities [5]. Hence, it significantly reduces the risk to the positioning navigation timing (PNT) services of the system. The eLoran system has been deployed as an independent land-based PNT system in several regions worldwide [6]. Although eLoran and satellite-based GNSS operate independently, they can complement each other.  
Timing monitoring is essential to ensure the reliable operation of timing systems. In November 2007, the eLoran Definition Document V1.0, published by the International Loran Association, specified that the eLoran system comprises eLoran signals, transmitters, control centres, monitoring stations, and user equipment, which collectively form the complete process from signal transmission to monitoring and usage [7, 8]. The establishment of an eLoran transmitter requires a timing monitoring station to monitor the quality of the broadcast signal. Hence, the station is a critical component in the design and operation of the eLoran system [9, 10].  
Recently, with the development of high-precision, ground-based timing systems and China's plan to establish three eLoran timing stations, many scholars have focused on the timing performance of eLoran systems [11]. According to the literature, research by both domestic and international scholars has primarily focused on evaluating the system's navigation performance and navigation accuracy.  
[PERSON] et al. evaluated the ground-wave propagation, atmospheric noise, transmitter and receiver performance, and overall system engineering in terms of integrity, availability, continuity, and accuracy [12]. [PERSON] et al. examined an additional secondary factor (ASF) and found that the predicted ASF aligned with the measured ASF, displaying an error of approximately 0.8 us and thereby validating ASF predictions [13]. [PERSON] demonstrated the positioning accuracy of eLoran in narrow South Korean waterways using improved ASF maps [14]. [PERSON] established an ASF data grid based on existing data [15].  
However, few studies have focused on eLoran timing monitoring and evaluations, with most addressing the navigation performance of a system to determine its viability as a GNSS backup [16; 17; 18]. Existing studies have not established a comprehensive timing monitoring and evaluation index system based on monitoring data analyses, nor have they provided detailed parameters or evaluation guidelines for eLoran timing monitoring. To address these problems, this study employed measurement methods to test and compare two commercial eLoran navigation timing monitoring receivers. This study also explored the signal reception strength and signal-to-noise ratio of each device and tested their timing accuracy and stability using the Xuancheng station as the benchmark. This approach quantified the timing capability of the eLoran system and provided technical references for enhancing its service capabilities.