• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.48 no.3
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• pp.235-241
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• 2012

The efficiency tests of automatic positioning transmitter (APT) using satellite on life jacket were carried out to minimize casualties of fishermen and to make system optimization for effective SAR (Search and Rescue) operation. As the result of the tests, average position was equaled on the comparison between SPOT using low earth orbit satellite and DGPS (Differential Global Positining System), but standard deviation of DGPS for latitude and longitude were 66.4% and 46.3% smaller than those of SPOT. The position precision of SPOT was almost two times lower than LGT using geostationary satellite to compare 95% circular error probability. However, the success rate of receiver for SPOT was revealed as 86.5~94.1% on the experiments in the South Sea and the West Sea and it was 4.5 times higher than LGT. Therefore, SPOT is expected to contribute greatly to the rapid rescue of victim.

• Journal of Advanced Navigation Technology
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• v.16 no.5
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• pp.752-759
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• 2012

In this paper, near-real-time positioning accuracies of precise point positioning technique were analyzed using IGS predicted orbits. As a result, we could get the mean errors of 1~1.6 cm, standard deviation of 1~1.3cm from one year of GPS data. This results were similar level to positioning accuracy using the IGS rapid orbits. Positioning errors of >10cm showed 44% of observed days of orbital anomalies. When the orbital anomalies of the predicted orbits were shown, maximum error was 1.7 km, and maximum of mean errors was 308 m. From this study, we conclude that check and consideration were necessary before using the IGS predicted orbits.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.4
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• pp.335-342
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• 2023

Lunar Navigation Satellite System refers to a constellation of satellite providing PNT services on the moon. LNSS consists of main satellite and navigation satellites. Navigation satellites orbiting around the moon and a main satellite moves the area between the moon and the L2 point. The navigation satellite performs the same role as the Earth's GNSS satellite, and the main satellite communicates with the Earth for time synchronization. Due to the effect of the non-uniform shape of the moon, it is necessary to focus on the influence of the lunar gravitational field when designing the orbit simulation for navigation satellite. Since the main satellite is farther away from the moon than the navigation satellite, both the earth's gravity and the moon's gravity must be considered simultaneously when designing the orbit simulation for main satellite. Therefore, the main satellite orbit simulation must be designed through the three-body problem between the Earth, the moon, and the main satellite. In this paper, the orbit simulation tool for main satellite and navigation satellite required for LNSS was designed. The orbit simulation considers the environment characteristics of the moon. As a result of comparing long-term data (180 days) with the commercial program GMAT, it was confirmed that there was an error of about 1 m.

• Journal of Positioning, Navigation, and Timing
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• v.1 no.1
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• pp.59-64
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• 2012

Precise Point Positioning (PPP) has been widely used in navigation and orbit determination applications as we can obtain precise Global Positioning System (GPS) satellite orbit and clock products. Kinematic PPP, which is based on the GPS measurements only from the spaceborne GPS receiver, has some advantages for a simple precise orbit determination (POD). In this study, we developed kinematic PPP technique to estimate the orbits of GRACE-A satellite. The comparison of the mean position between the JPL's orbit product and our results showed the orbit differences 0.18 cm, 0.54 cm, and 0.98 cm in the Radial, in Along-track, and Cross-track direction respectively. In addition, we obtained the root mean square (rms) values of 4.06 cm, 3.90 cm, and 3.23 cm in the satellite coordinate components relative to the known coordinates.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.3
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• pp.173-179
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• 2022

The satellite navigation deception technology disturbs the navigation solution of the receiver by generating a deceptive signal simulating the actual satellite for the satellite navigation receiver mounted on the unmanned aerial vehicle, which is the target of deception. A single spoofing technique that creates a single deceptive position and velocity can be divided into a synchronized spoofing signal that matches the code delay, Doppler frequency, and navigation message with the real satellite and an unsynchronized spoofing signal that does not match. In order to generate a signal synchronized with a satellite signal, a very sophisticated and high precision signal generation technology is required. In addition, the current position and speed of the UAV equipped with the receiver must be accurately detected in real time. Considering the detection accuracy of the current radar technology that detects small UAVs, it is difficult to detect UAVs with an accuracy of less than one chip. In this paper, we assume the asynchrony of a single spoofing signal and propose a region defense technique using multiple spoofing signals.

• Journal of Positioning, Navigation, and Timing
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• v.1 no.1
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• pp.7-14
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• 2012

Due to inaccurate safe navigation estimates, maritime accidents have been occurring consistently. In order to solve this, the precise positioning technology using carrier phase information is used, but due to high buildings near inland waterways or inclination, satellite signals might become weak or blocked for some time. Under this weak signal environment for some time, the GPS raw measurements become less accurate so that it is difficult to search and maintain the integer ambiguity of carrier phase. In this paper, a method to generate code and carrier phase measurements under this environment and maintain resilient navigation is proposed. In the weak signal environment, the position of the receiver is estimated using an inertial sensor, and with this information, the distance between the satellite and the receiver is calculated to generate code measurements using IGS product and model. And, the carrier phase measurements are generated based on the statistics for generating fractional phase. In order to verify the performance of the proposed method, the proposed method was compared for a fixed blocked time. It was confirmed that in case of a weak or blocked satellite signals for 1 to 5 minutes, the proposed method showed more improved results than the inertial navigation only, maintaining stable positioning accuracy within 1 m.

• Journal of Positioning, Navigation, and Timing
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• v.8 no.1
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• pp.31-40
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• 2019

In recent years, Intelligent Transport Systems (ITS) and Autonomous Vehicle Technology have actively studied around the world. In order to achieve the purpose of Advanced Driver Assistance System (ADAS) and Autonomous Vehicle Technology, it must be obtained accurate and reliable positioning. However, the problem of positioning in the urban area is a low position accuracy caused by the reduction of the number of visible satellites due to high buildings. In this paper, we analyzed the availability of precise positioning system in urban area are using GPS/BDS integrated system. For this study, GPS and BDS satellite signals were collected using two low-cost receivers in the open sky and a designed software based platform for precise positioning performance analysis. And we analyzed the precise positioning performance by changing the mask angle considering the urban area. From the results, it can be confirmed that the performance of precise positioning of GPS only and BDS only decrease in the environment where mask angle is $40^{\circ}$ to $45^{\circ}$, however, GPS/BDS integrated system maintains high performance of precise positioning.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.3
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• pp.323-332
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• 2023

Today, services using Positioning, Navigation, and Timing (PNT) technology are provided in various fields, such as smartphone Location-Based Service (LBS) and autonomous driving. Generally, outdoor positioning techniques depend on the Global Navigation Satellite System (GNSS), and the need for positioning techniques that guarantee positioning accuracy, availability, and continuity is emerging with advances in service. In particular, continuity is not guaranteed in urban canyons where it is challenging to secure visible satellites with standalone GNSS, and even if more than four satellites are visible, the positioning accuracy and stability are reduced due to multipath channels. Research using Low Earth Orbit (LEO) satellites is already underway to overcome these limitations. In this study, we conducted a trend analysis of LEO-PNT research, an LEO satellite-based navigation and augmentation system. Through comparison with GNSS, the differentiation of LEO-PNT was confirmed, and the system design and receiver processing were analyzed according to LEO-PNT classification. Lastly, the current status of LEO-PNT development by country and institution was confirmed.

• Journal of Advanced Navigation Technology
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• v.14 no.6
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• pp.783-790
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• 2010

For safety navigation of ships at sea, ships monitor their location obtained from Global Positioning Satellite System (GNSS). In this study, we computed near-real-time positions of a ship at sea using GPS Precise Point Positioning (PPP) technique and analyzed precision of the near-real-time positions. We conducted ship borne GPS observations in the south sea of Korea. To process the GPS data using PPP technique, GIPSY-OASIS (GPS Inferred Positioning System-Orbit Analysis and Simulation Software) developed by the Jet Propulsion Laboratory was used. Antenna phase center variations, ocean tidal loading displacements, and azimuthal gradients of the atmosphere were corrected or estimated as standard procedures of high-precision GIPSY-OASIS data processing. As a result, the precisions of near-real-time positions was ~1cm.