• Journal of Institute of Control, Robotics and Systems
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• v.16 no.2
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• pp.188-193
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• 2010

With GPS being the primary navigation system, Loran use is in steep decline. However, according to the final report of vulnerability assessment of the transportation infrastructure relying on the global positioning system prepared by the John A. Volpe National Transportation Systems Center, there are current attempts to enhance and re-popularize Loran as a GPS backup system through the characteristic of the ground based low frequency navigation system. To advance the Loran system such as Loran-C modernization and eLoran development, research is definitely needed in the field of Loran-C receiver signal processing as well as Loran-C signal design and the technology of a receiver. We have developed a set of Matlab tools, which implement a software Loran-C receiver that performs the receiver's position determination through the following procedure. The procedure consists of receiving the Loran-C signal, cycle selection, calculation of the TDOA and range, and receiver's position determination through the Least Square Method. We experiences the effect of an incorrect cycle selection and various error factors (ECD, ASF, sky wave, CRI, etc.) from the result of the Loran-C signal processing. It is apparent that researches which focus on the elimination and mitigation of various error factors need to be investigated on a software Loran-C receiver. These aspects will be explored in further work through the method such as PLL and Kalman filtering.

• Journal of the Institute of Convergence Signal Processing
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• v.12 no.2
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• pp.107-112
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• 2011

Several developed countries have been developing their own satellite navigation systems, such as Europe's Galileo, China's BEIDOU, and Japan's QZSS, to cope with clock errors and signal vulnerabilities of GPS. In addition, modernization of Loran, eLoran, for GPS backup has been conducted. In Korea, a dependent navigation system has been required and for GPS backup, the need for utilization of time synchronization infrastructure through the modernization of Loran has been raised. Loran signal uses 100Khz groundwave. A significant factor limiting the ranging accuracy of the Loran signal is the ASF arising from the fact that the groundwave signal is likely to propagate over paths of varying conductivity and topography. Thus, an ASF compensation method is very important for Loran and eLoran navigation. This paper introduces the propagation delay model and then compares and analyzes the estimations from the propagation delay model and measured ASFs.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2017.11a
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• pp.190-192
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• 2017

The manufacture of current Loran-C signal receiver has been discontinued and there are no spare parts for that. eLoran system is being developed. Judging from these facts, it is necessary to purchase eLoran receivers which also can receive Loran-C signal. Furthermore, the coverage of Loran-C has been decreased as the closure of transmitting stations in Japan. The current monitor station in Ganjeolgot, Ulsan shall be moved to a new place.

• Journal of Positioning, Navigation, and Timing
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• v.2 no.2
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• pp.101-108
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• 2013

GPS is the most widely-used Positioning, Navigation, and Timing (PNT) system. Since GPS is an important PNT infrastructure, the vulnerability of GPS to signal jamming has received significant attention. Especially, South Korea has experienced intentional high-power jamming from North Korea for the past three years, and thus realized the necessity of a complementary PNT system. South Korea recently decided to deploy a high-power terrestrial navigation system, eLoran, as a complementary PNT system. According to the plan, the initial operational capability of the Korean eLoran system is expected by 2016, and the full operational capability is expected by 2018. As a necessary research tool to support the Korean eLoran program, an eLoran performance simulation tool for Korea is under development. In this paper, the received signal strength, which is necessary to simulate eLoran performance, from the suggested Korean eLoran transmitters is simulated with the consideration of effective ground conductivities over Korea. Then, eLoran signal-to-noise ratios are also simulated based on atmospheric noise data over Korea. This basic simulation tool will be expanded to estimate the navigation performance (e.g., accuracy, integrity, continuity, and availability) of the Korean eLoran system.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.3
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• pp.229-234
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• 2021

In this paper, a study was conducted on the power amplifier control required to design an eLoran transmitter system using a low-height antenna. The eLoran transmitter developed during the eLoran technology development project conducted in Korea used a small 35 m antenna due to the difficulty of securing a site for antenna installation. This antenna height is very low compared to the height of 750 m which is required for eLoran 100 kHz signal transmission without any radiation loss. In the case of using such a small antenna, not only the radiation efficiency of the transmission is lowered, but also the power module control must be performed more precisely in order to transmit the eLoran standard signal. The equivalent RLC circuit of the transmitter system was implemented and transient analysis was conducted to derive the input required voltage for satisfying the output requirement. The voltage waveform was also generated by the RLC circuit analysis to generate the eLoran signal. Furthermore, we suggest power width modulation method to control eLoran power amplifier module more sophisticatedly.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.2
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• pp.153-158
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• 2021

In order to mitigate the vulnerability of the satellite navigation system against radio frequency interference, South Korea has been developing advanced terrestrial navigation system (eLoran) technology since 2016. The eLoran system synchronizes the transmission time of the pulse used in the existing Loran-C system with UTC and transmits correction information that can improve the position error. The eLoran system is known to reduce the position error of about 460 m of the existing Loran-C system to 20 m, and for this, the transmitter must be able to transmit eLoran signals according to more stringent standards. For this reason, an international standard that further developed the Loran-C signal standard established by US Coast Guard was established by Society of Automotive Engineers (SAE) International. In this paper, based on the analysis of the SAE9990 document, the international standard for eLoran transmission signals, a standard inspection process was produced to check whether the eLoran transmitter is transmitting signals in accordance with the standard.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.1
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• pp.23-28
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• 2022

The eLoran system is a high-power terrestrial navigation system that is recognized as the most appropriate alternative to complement the GNSS's vulnerability to radio frequency interference. Accordingly, Korea has conducted eLoran technology development projects since 2016. The eLoran system developed in Korea provides 20 m positioning accuracy to maritime user in Incheon and Pyeongtaek harbor. To accurately calculate the position with the eLoran signal, it is necessary to apply a compensation method that mitigates the propagation delay. In this paper, we develop the compensation method to mitigate the eLoran signal propagation delay and evaluate the positioning performance in Incheon harbor. The propagation delay due to the terrain characteristics is pre-surveyed and stored in the user receiver. Real-time fluctuations in propagation delay compared to the pre-stored data are mitigated by the temporal correction generated at a nearby differential Loran station. Finally, two performance evaluation tests were performed to verify the positioning accuracy of the Korean eLoran system. The first test took place in December 2020 and the second in April 2021. As a result, the Korean eLoran service has been confirmed to provide 20 m location accuracy without GPS.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2017.11a
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• pp.193-195
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• 2017

This paper focuses on development status of eLoran system which is an representative backup PNT system in order to overcome the vulnerability of GNSS signals by radio frequency interference such as jamming. eLoran testbed system consists of new transmitting system for amplifying the signal through signal generation and modulation, differential Loran (dLoran) reference stations for calculating the signal errors received from transmitters, an integrated operation and control system (IOCS) for eLoran service. Therefore we present the configuration of testbed architecture for trial operation of eLoran service and the development status, and discuss about the next step toward backup PNT service using eLoran system.

• Journal of Advanced Navigation Technology
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• v.23 no.4
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• pp.289-295
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• 2019

Maritime back-up navigation system in port approach requires a horizontal accuracy of 10 meters in IALA (International Association of Lighthouse Authorities) recommendations. eLoran which is a best back-up navigation system that satisfies accuracy requirement has poor navigation performance depending signal environments. Especially, noise caused by multipath and electronic devices around eLoran antenna affects navigation performance. In this paper, Ship based Navigation Back-up system using UAV on Interference is designed to satisfy horizontal accuracy requirement. To improve the eLoran signal environment, UAVs are equipped with camera, IMU sensor and eLoran antenna and receivers. This proposed system is designed to receive eLoran signal through UAV-based receiver and control UAV's position and attitude within Landmark around area. The ship-based positioning using eLoran signal, vision and attitude information received from UAV satisfy resilient and robust navigation requirements.

• Journal of information and communication convergence engineering
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• v.5 no.4
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• pp.295-299
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• 2007

This paper presents the ASF(Additional Secondary Factor) modeling of DGPS beacon signal. In addition to DGPS's original purpose, the feasibility to utilize DGPS system for timing and navigation has been studied. For timing and navigation, the positioning system must know the accurate time delay of signal traveling from the transmitter to receiver. Then the delay can be used to compute the user position. The DGPS beacon signal transmits the data using medium frequency, which travels through the surface and cause the additional delay rather than the speed of light according to conductivities and elevations of the irregular terrain. We introduce the modeling of additional delay(ASF) and present the results of implementation. The similar approach is Locan-C. Loran-C has been widely used as the maritime location system and was enhanced to E-Loran(Enhanced Loran). E-Loran system uses the ASF estimation method and is able to provide the more precise location service. However there was rarely research on this area in Korea. Hence, we introduce the ASF and its estimation model. With the comparison of the same condition and data from the original Monteath model and ASF estimation data of Loran system respectively, we guarantee that the implementation is absolutely perfect. For further works, we're going to apply the ASF estimation model to Korean DGPS beacon system with the Korean terrain data.