• Journal of the Korean Society for Aviation and Aeronautics
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• v.22 no.3
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• pp.74-81
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• 2014

The coverage area of GNSS regional ionospheric correction model is mainly determined by the disribution of GNSS ground monitoring stations. Outside the coverage area, GNSS users may receive ionospheric correction signals but the correction does not contain valid correction information. Extrapolation of the correction information can extend the coverage area to some extent. Three interpolation methods, Kriging, biharmonic spline and cubic spline, are tested to evaluate the extrapolation accuracy of the ionospheric delay corrections outside the correction coverage area. IGS (International GNSS Service) ionosphere map data is used to simulate the corrections and to compute the extrapolation error statistics. Among the three methods, biharmonic method yields the best accuracy. The estimation error has a high value during Spring and Fall. The error has a high value in South and East sides and has a low value in North side.

• Journal of Advanced Navigation Technology
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• v.14 no.6
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• pp.800-807
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• 2010

Jack knifing accident of semi trailer vehicle is one of the most dangerous accident type because the vehicle cross over its lane by the accident. Jack knifing accident can be predicted and detected by GNSS precise relative positioning. But integer ambiguity resolution procedure is inevitable in GNSS precise relative positioning. In this paper, success rate improving method of integer ambiguity resolution is proposed for jack knifing accident prediction and detection of semi trailer vehicle, and proposed method is tested by simulation.

• The Journal of Korea Robotics Society
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• v.18 no.1
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• pp.72-81
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• 2023

We introduce tightly-coupled GNSS-LiDAR-Inertial state estimator, which is capable of SLAM (Simultaneously Localization and Mapping) and autonomous driving. Long term drift is one of the main sources of estimation error, and some LiDAR SLAM framework utilize loop closure to overcome this error. However, when loop closing event happens, one's current state could change abruptly and pose some safety issues on drivers. Directly utilizing GNSS (Global Navigation Satellite System) positioning information could help alleviating this problem, but accurate information is not always available and inaccurate vertical positioning issues still exist. We thus propose our method which tightly couples raw GNSS measurements into LiDAR-Inertial SLAM framework which can handle satellite positioning information regardless of its uncertainty. Also, with NLOS (Non-light-of-sight) satellite signal handling, we can estimate our states more smoothly and accurately. With several autonomous driving tests on AGV (Autonomous Ground Vehicle), we verified that our method can be applied to real-world problem.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.15 no.2
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• pp.18-24
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• 2007

The high ionospheric spatial gradient during ionospheric storm is the most concern when applying GNSS(Global Navigation Satellite System) augmentation systems for aircraft precision approach. Since the ionospheric gradient level depends on geographical location as well as the storm, understanding the ionospheric gradient statistics over a specific regional area is necessary for operating the augmentation systems. This paper compares three ionosphere gradient computation methods, direct differentiation between two receivers' ionospheric delay signal for a common satellite, derivation from a grid ionosphere map, and derivation from a plate ionosphere map. The plate map method provides a good indication on the gradient variation behavior over a regional area with limited number of GNSS receivers. The residual analysis for the ionosphere storm detection is discussed as well.

• Journal of Positioning, Navigation, and Timing
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• v.7 no.3
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• pp.175-181
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• 2018

The use of dual-frequency measurements from the Global Navigation Satellite System (GNSS) enables us to observe precise ionospheric total electron content (TEC). Currently, many GNSS reference stations in South Korea provide both GPS and GLONASS data. In the present study, we estimated the grid-based TEC values and relative receiver differential code biases (DCB) from a GNSS network operated by the Korea Astronomy and Space Science Institute. In addition, we compared the diurnal variations in a TEC time series from solutions of the GPS only, the GLONASS only, and combined GPS/GLONASS processing. A significant difference between the GPS only TEC and combined GPS/GLONASS TEC at a specific grid point over South Korea appeared near the solar terminator. It is noted that GLONASS measurements can contribute to observing a variation in ionospheric TEC over high latitude regions.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.37 no.4
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• pp.233-242
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• 2019

ZHD (Zenith Hydrostatic Delay) model is important parameter in estimating of GNSS (Global Navigation Satellite System) PWV (Precipitable Water Vapor) along with weighted mean temperature. The ZWD (Zenith Wet Delay) is tend to accumulate the ZHD error, so that biases from ZHD will be affected on the precision of GNSS PWV. In this paper, we compared the accuracy of GNSS PWV with radiosonde PWV using three ZHD models, such as Saastamoinen, Hopfield, and Black. Also, we adopted the KWMT (Korean Weighted Mean Temperature) model and the mean temperature which was observed by radiosonde on the retrieval processing of GNSS PWV. To this end, GNSS observation data during one year were processed to produce PWVs from a total of 5 GNSS permanent stations in Korea, and the GNSS PWVs were compared with radiosonde PWVs for the evaluating of biases. The PWV biases using mean temperature estimated by the KWMT model are smaller than radiosonde mean temperature. Also, we could confirm the result that the Saastamoinen ZHD which is most used in the GNSS meteorology is not valid in South Korea, because it cannot be exclude the possibility of biases by latitude or height of GNSS station.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.7
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• pp.689-694
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• 2008

This paper proposes a roll rate estimation method for spinning vehicles. The carrier phase and frequency variations caused by spinning of vehicles are observed and the roll rate estimator is designed on the observation. The roll rate estimator consists of phase detector and zero crossing counter. The phase detector computes phase variation using in-phase and quadrature value from the correlator. By using zero crossing counter, the roll rate can be estimated since the output of phase detector is changed in proportion to the roll rate. Experiment a results show that estimated roll rate error is smaller than 0.0578Hz.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.3
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• pp.191-198
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• 2022

In order to increase the practical use and navigational application performance of the Korean Positioning System (KPS), it is required to provide interoperability with other Global Navigation Satellite System (GNSS). This kind of interoperability can be obtained by broadcasting the time offset between KPS and GNSS using a KPS navigation message. With the assumption that KPS Time (KPST) will be generated by the similar method and equipment of UTC(KRIS), the overall behavior of KPST will be close to that of UTC(KRIS). Therefore, the time offset between KPST and GPS Time (GPST) is estimated by using UTC(KRIS) instead of KPST because KPST can not available at the present time. In this paper, we describe the estimation results of the KPS to GPS Time Offset (KGTO) obtained by using a GNSS time transfer receiver which reference inputs are fed from UTC(KRIS). The estimated KGTO performance is compared to the time offset between UTC(KRIS) and UTC(USNO) which is used to generate GPST and considered as the real GPST. The time offset between UTC(KRIS) and UTC(USNO) is obtained by using the Bureau International des Poids et Mesures (BIPM) Circular T report. From the results, it is observed that KGTO can be estimated under 10 ns with the assumption that KPST will be generated by a similar method of UTC(KRIS) generation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6C
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• pp.505-511
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• 2008

The global navigation satellite system (GNSS) is using a direct sequence/spread spectrum (DS/SS) modulation. In order to recover the information data, the DS/SS system first performs a two-step synchronization process: acquisition and tracking. The acquisition process adjusts the phase difference between the received and locally generated acquisition sequences within ${\pm}T_c/2$ or less, where $T_c$ is the chip period. The tracking process performs fine synchronization. In this paper, we focus on the tracking issue. The single delta delay locked loop($\Delta$-DLL) is the optimal tracking scheme for a GNSS in the absence of multipath signals, where $\Delta$ means the spacing between the early and late correlation time offset. In the multipath environments, however, the $\Delta$-DLL suffers from huge estimation bias(denoted by $\beta$) caused by distorted correlation values. Although some modified schemes such as a $\Delta$-DLL with a narrow $\Delta$ and a double delta DLL (${\Delta}^{(2)}$-DLL) were proposed to reduce the estimation bias, they cannot remove the estimation bias completely and need more accurate acquisition process. This paper proposes a novel tracking scheme that can dramatically reduce the estimation bias, using the maximum slope change among the correlation outputs.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.10
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• pp.1073-1078
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• 2014

In this paper, an effective repeat-back jamming (RBJ) mitigation scheme known assuccessive repeat-back jamming cancellation (SRC) is proposed for the utilization of the successive interference cancellation (SIC) algorithm which is used to mitigate the near-far effect and the multiple-access interference for code division multiple-access communication systems. The proposed scheme uses a combined pseudo-random noise (C-PRN) signal from the estimated major parameters of RBJ signals. To evaluate the performance of the proposed scheme, the root mean squared (RMS) code tracking errors are shown according to the standard deviation of the parameter estimation errors of an RBJ signal, and using the well-known major parameters estimation schemes with a C-PRN signal through Monte-Carlo simulation.