• Journal of Advanced Navigation Technology
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• v.24 no.6
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• pp.533-539
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• 2020

Real-time service (RTS) provided by IGS provides correction for GNSS orbit and clock via internet, so it is widely used in fields that require real-time precise positioning. However, the RTS signal may be lost due to an unstable Internet environment. When signal disconnection occurs, signal prediction can be performed using polynomial models. However, the RTS changes rapidly after the GNSS navigation message issue of data (IOD) changes, so it is difficult to predict when signal loss occurs at that point. In this study, we proposed an algorithm to generate continuous RTS correction information by applying the difference in navigation trajectory according to IOD change. The use of this algorithm can improve the accuracy of RTS prediction at IOD changes. After performing optimization studies to improve RTS prediction performance, the predicted RTS trajectory information was applied to precision positioning (PPP). Compared to the conventional method, the position error is significantly reduced, and the error increase along with the signal loss interval increase is reduced.

• Journal of Advanced Navigation Technology
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• v.26 no.6
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• pp.418-426
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• 2022

Unlike OSR(observation space representation), the SSR(state space representation) augmentation system is suitable for a one-way broadcasting service because it provides the same corrections to all users in the service area. Due to this advantage, several GNSS(global navigation system) systems such as Galileo, BDS(beidou navigation satellite system), QZSS(quasi zenith satellite system) are establishing PPP (precise point positioning)/PPP-RTK precision positioning services based on SSR messages. Therefore, in this paper, we try to understand the trends of satellite-based PPP/PPP-RTK correction services by analyzing the system configurations, characteristics, and precise positioning performance of satellite-based SSR correction broadcasting services.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.3
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• pp.281-288
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• 2023

The International Maritime Organization (IMO) states that the recommended horizontal accuracy for coastal and offshore areas is 10 m, the Alert Limit (AL) is 25 m, the time to alert is 10 seconds, and the integrity risk (IR) is 10^-5 per three hours. For operations requiring high accuracy, such as tugs and pushers, icebreakers, and automated docking, the IMO dictates that a high level of positioning accuracy of less than one meter and a protection level of 0.25 meters (for automated docking) to 2.5 meters should be achieved. In this paper, we analyze a method of calculating the user-side protection level of the centimeter-level precision Global Navigation Satellite System (GNSS) that is being studied to provide augmentation information for the precision Positioning, Navigation and Timing (PNT) service. In addition, we analyze standardized integrity forms based on RTCM SC-134 to propose an integrity information form and generate a centimeter-level precise PNT service plan.

• Proceedings of the Korea Contents Association Conference
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• 2008.05a
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• pp.902-905
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• 2008

With development of internet, location-based service (LBS) is getting more interest in wire and wireless network, and many studies are in progress to provide various services such as GIS and GPS technique related to this. Today positioning and information providing service is accomplished by mobile communication companies' chasing the cell or building unique GIS system, but there is a lot of building-cost that must be endured to define boundary of collecting precise location information from chasing Cell and provide unique location information service. In this paper, it desires to make the database of location information with using GPS, relatively precise satellite positioning system, to cut the cost of building location information service, and to present service models such as children's positioning service that is to reduce the cost of building GIS by using Web Open API and provide location information of discrete object in real-time.

• The KIPS Transactions:PartC
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• v.13C no.1 s.104
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• pp.95-102
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• 2006

Nowadays, GPS is used widely, especially in case which needs precise position information, such as car navigation systems and various kinds of position measuring instruments in an outdoor environment. According to their applications, there are many kinds of GPS receivers with different costs and error rates. The maximum error range of the general-purpose GPS receiver is within 30m, though the error rate depends on receiving rate of signal and weather condition. RTK(Real-Time Kinematic) and DGPS(Differential Global Positioning System) have more precise accuracy than the general-purpose GPS. However end users can't afford use them because of their high price and large size of equipments. In order for the end user to obtain precise position information, it is important that GPS receivers has portability and low price. In this study, we introduce a new system that offers precise position information using the DGPS mechanism satisfying low cost and portability.

• Journal of Positioning, Navigation, and Timing
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• v.3 no.3
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• pp.123-129
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• 2014

The real-time kinematic (RTK) is one of precise positioning methods using Global Positioning System (GPS) data. In the long baseline GPS RTK, the ionospheric and tropospheric delays are critical factors for the positioning accuracy. In this paper we present RTK algorithms for long baselines more than 100 km with estimating tropospheric delays. The state vector is estimated by the extended Kalman filter. We show the experimental results of GPS RTK for various baselines (162.10, 393.37, 582.29, and 1283.57 km) by using the Korea Astronomy and Space Science Institute GPS data and one International GNSS Service (IGS) reference station located in Japan. As a result, we present that long baseline GPS RTK can provide the accurate positioning for users less than few centimeters.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.4
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• pp.263-268
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• 2022

Precise Point Positioning-Real Time Kinematic (PPP-RTK) is a high accuracy positioning method that combines RTK and PPP to overcome the limitations on service coverage of RTK and convergence time of PPP. PPP-RTK provides correction data in the form of State Space Representation (SSR), unlike RTK, which provides measurement-based Observation Space Representation (OSR). Due to this, PPP-RTK has an advantage that it can transmit less data than RTK. So, recently, several techniques for PPP-RTK have been proposed. However, in order to utilize PPP-RTK techniques, performance analysis of these in a real environment is essential. In this paper, we implement the local network PPP-RTK and analyze the positioning performance according to the distance within 100 km from the reference station in Korea. As results of experiment, the horizontal and vertical 95% errors of local network PPP-RTK were 6.25 cm and 5.86 cm or less, respectively.

• Korean Journal of Remote Sensing
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• v.19 no.3
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• pp.181-190
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• 2003

Since the operation of the first satellite-based navigation service, satellite positioning has played an increasing role in both surveying and geodesy, and has become an indispensable tool for precise relative positioning. However, in some situations, e.g. at a low angle of elevation, the use of satellites for navigation is seriously restricted because obstacles like buildings and mountains can block signals. As a mean to resolve this problem, the quasi-zenith satellite system has been proposed as a next-generation satellite navigation system. Quasi-zenith satellite is a system which simultaneously deploys several satellites in a quasi-zenith geostationary orbit so that one of the satellites always stay close to the zenith if viewed from a specific point on the ground of East Asia. Thus, if a position measurement function compatible with CPS is installed in the quasi-zenith and stationary satellites, and these satellites are utilized together with the CPS, four satellites can be accessed simultaneously nearly all day long and a substantial improvement in position measurement, especially in metropolitan areas, can be achieved. The purpose of this paper is to evaluate the effectiveness of quasi-zenith satellite system on positioning accuracy improvement through simulation by using precise orbital information of the satellites and a three-dimensional digital map. Through this developed simulation system, it is possible to calculate the number of simultaneously visible satellites and available area for positioning without the need of actual observation. Furthermore, this system can calculate the Dilution Of Precision (DOP) and the error distribution.

• Journal of Positioning, Navigation, and Timing
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• v.12 no.4
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• pp.349-358
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• 2023

The Satellite-Based Augmentation System (SBAS) plays a significant role in the fields of aviation and navigation: it corrects signal errors of the Global Navigation Satellite System (GNSS) and provides integrity information to facilitate precise positioning. These SBAS systems have been adopted as international standards by the International Civil Aviation Organization (ICAO). In recent SBAS system design, the Minimum Operational Performance Standards (MOPS) defined by the Radio Technical Commission for Aeronautics (RTCA) must be followed. In October 2014, South Korea embarked on the development of a Korean GPS precision position correction system, referred to as Korea Augmentation Satellite System (KASS). The goal is to achieve APV-1 Standard of Service Level (SoL) service level and acquisition of CAT-1 test operating technology. The first satellite of KASS, KASS Prototype 1, was successfully launched from the Guiana Space Centre in South America on June 23, 2020. In December 2022 and June 2023, the first and second service signals of KASS were broadcasted, and full-scale KASS correction signal broadcasting is scheduled to start at the end of 2023. The aim of this study is to analyze the precision of both the GNSS system and KASS system by comparing them. KASS is also compared with Japan's Multi-functional Satellite Augmentation System (MSAS), which is available in Korea. The final objective of this work is to validate the usefulness of KASS correction navigation in the South Korean operational environment.