• Journal of Navigation and Port Research
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• v.37 no.3
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• pp.263-267
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• 2013

This paper describes the progress and the plan of 'Wide Area Differential GPS (WA-DGPS) Development' project supported by Korean Ministry of Oceans and Fisheries. The project develops the main algorithms of the WA-DGPS which guarantees the improved accuracy, availability, and integrity all over the Korean peninsula. After the establishment of WA-DGPS ground infrastructure system, a real-time demonstration using pseudolite installed on the ground will be conducted in the final year. Also, the development of Korean Satellite-based Augmentation System (SBAS) is expected to be started from 2014, and the algorithms and the results in the WA-DGPS project will be used in the SBAS development.

• Journal of Satellite, Information and Communications
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• v.10 no.3
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• pp.38-43
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• 2015

This paper describes a GPS signal generator that can generate multiple satellite signals in real time at the RF level. It realizes the verified software algorithm on a FPGA. The algorithm models orbits and environmental errors such as ionospheric and tropospheric multipath. The position of a simulated receiver is one of simulation parameters. The hardware which consists of a digital logic board and an analog board can generate 16 simulated satellites signals at the same time. The users can generate spoofing signals and jamming signals as well as satellite signals by using the windows-based control software. In addition, the software provides GIS-based simulation scenarios editing tools. We verified the generator by using commercial receivers. As an application, we configured generators as indoor positioning systems and tested them in a building. To improve the accuracy of indoor systems is our further study.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.17 no.5
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• pp.160-172
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• 2018

The method of estimating a position using a GPS has been applied to various fields including a navigation system of an automobile. However, since it is difficult to measure GPS signals indoors, it is difficult to locate specific objects indoors such as a building or factory. To overcome these limitations, this study proposes a system for object location estimation based on Bluetooth5 for the management of materials in factories. The object position estimation system consists of a Bluetooth signal generator, a receiver, and a database server. A signal generator based on Bluetooth Low Energy(BLE) is attached to the material and a receiver is appropriately arranged inside the factory. In this study, we propose "Diagonal Survey Method", a 4 - axis survey algorithm using four receivers to reduce the error of existing trilateration method. The proposed algorithm showed good performance compared to the conventional trilateration and we verified the effectiveness of the proposed system and algorithm by performing the experiment by installing the system in the factory.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.2
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• pp.288-295
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• 2011

The paper proposes a localization method of an underwater robot using Monte Carlo Localization(MCL) approach. Localization is one of the fundamental basics for autonomous navigation of an underwater robot. The proposed method resolves the problem of accumulation of position error which is fatal to dead reckoning method. It deals with uncertainty of the robot motion and uncertainty of sensor data in probabilistic approach. Especially, it can model the nonlinear motion transition and non Gaussian probabilistic sensor characteristics. In the paper, motion model is described using Euler angles to utilize the MCL algorithm for position estimation of an underwater robot. Motion model and sensor model are implemented and the performance of the proposed method is verified through simulation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.11
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• pp.2021-2032
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• 1992

A redundant sensor system, which consists of two incremental encoders and a gyro sensor, has been proposed for the estimation of the posture of mobile robots. A hardware system was built for estimating the heading angle change of the mobile robot from outputs of the gyro sensor. The proposed hardware system of the gyro sensor produced an accurate estimate for the heading angle change of the robot. A sensor data fusion algorithm has been developed to find the optimal estimates of the heading angle change based on the stochastic measurement equations of our readundant sensor system. The maximum likelihood estimation method is applied to combine the noisy measurement data from both encoders and gyro sensor. The proposed fusion algorithm demonstrated a satisfactory performance, showing significantly reduced estimation error compared to the conventional method, in various navigation experiments.

• Geophysics and Geophysical Exploration
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• v.12 no.2
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• pp.208-214
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• 2009

Using the GNSS data and tilt-meter data of Boeun (BOEN) and Goesan (GSAN) GNSS stations, we have calculated the differential distance vector variation with the calculation time span set to 1 hour and 3 hour and differential tilt vector variation along time and derived an indicator of similarity between the two variations along time. The similarity such calculated is rather lower than high. But as the existence of a circular type movement of the antenna's phase center's location due to the tilt's variation of the antenna tower because of the sunlight's diurnal change is certain, we recommend to take such diurnal variation of antenna's location into consideration when the correction error in DGNSS or the measured data at reference stations in VRS (Virtual Reference System) is broadcast.

• Journal of Advanced Navigation Technology
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• v.18 no.4
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• pp.312-318
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• 2014

The altitudes of GEO satellites are higher than those of GPS satellites. Therefore the visibility and the received power of GPS signals are totally different from those of the users near the Earth's surface. In this study, we analyzed the visibility of GPS signals received on GEO satellites. And we also developed a software GPS receiver that works on GEO satellites using CCMDB algorithm which is a weak signal receiver algorithm. GPS signals received on a GEO satellite are generated by a commercial hardware GPS simulator and used for the verification of the developed software GPS receiver. The mean 3D position and velocity error are calculated as 165.636 m and 0.5081 m/s.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.10
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• pp.52-60
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• 2010

It is generally important to get a precise position information for autonomous unmanned vehicle(AUV) to run safely. For getting the position of AUV, the GPS has been using to navigation in a vehicle. Though it is useful to finding a position, it is difficult to precisely control a trajectory of the AUV due to large measuring error which may reach over 10 meters. Therefore to apply AUV it needs to compensate for the error. This paper proposes a method to more precisely localize AUV using three low-cost differential global positioning systems (DGPS). The distance errors between each DGPS are minimized as using the least square method (LSM) and the Kalman filter to eliminate a Gaussian white noise. The selected DGPS is cheaper and easier to set up than the RTK-GPS. It is also more precise than the general GPS. The proposed method can compensate the relatively position error according to stationary and moving distance of the AUV. For evaluating the algorithm by simulation, the DGPS signal with the Gaussian white noise to any points is generated by the AR model and compared with the measurement signal. It is confirmed that the proposed method can effectively compensate the position error as comparing with the measurement signal. The compensated position signal can be used to localize and control the AUV in the road.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.2
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• pp.171-177
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• 2012

In this paper, we proposed a algorithm and an operation boundary for fault detection of a onboard GNSS receiver. After aircraft exchange corrections computed by an aircraft receiver, a faulty aircraft receiver is detected by checking consistency of correction. For this purpose, PRC residual is used as the test statistic for fault detection of the onboard GNSS receiver. And operation boundaries are set by using DGPS position error increase with respect to the distance from a reference station. If the fault detection is performed by using aircraft only in operation boundary, the more accurate fault detection can be possible.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.31 no.4
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• pp.277-283
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• 2013

GPS RTK surveying has an issue that the positioning error increases as the base line distance between the reference station and rover station increases. However, nowadays, an accuracy assessment that can handle such issue is surely required because of the modernization of GLONASS, Galileo project, and other improvements of satellite receiving conditions. Therefore, in this research, we compared and analyzed data sets collected with the CORS network, placed at NGII and NDGPS, using Internet RTK surveying in different satellite receiving conditions. As a result, there was a negative effect on the positioning accuracy as the base line distance increases. Furthermore, we could collect quantitative data of the accuracy of RTK surveying. When national-wide GNSS system is fully established, this result will contribute the growth of various GNSS industries including survey industries and land survey industries.