• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.163-164
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• 2014

Pseudolite systems are used for backup systems of GPS satellite or indoor navigation systems. The pseudolite transmits GPS-like signal on the ground. Fundamentally, to estimate a position, clock synchronization among satellites is essential, because GPS receiver uses measurement based on TOA. Therefore, in order to improve the navigation performance in applications using pseudolite, clock synchronization with GPS satellites is required. This paper proposes design of monitoring system for pseudolite clock synchronization. The monitoring system analyzes clock synchronization accuracy of pseudolite and can be used for clock adjustment.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2013.10a
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• pp.370-371
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• 2013

현재 운영 중인 DGPS RSIM은 다중 GPS/GNSS 수신기를 이용하여 의사거리 기반 보정정보와 그 무결성 기능을 제공하고 있다. 기준국 시스템 기반 무결성 기능 강화를 위하여, 본 논문에서는 기준국 수신기를 기반으로 전파간섭을 검출할 수 있는 간이 기법과 모니터링 시스템에 대해 다룬다. 기준국 시스템에 전파간섭의 영향을 받게 되었을 경우, 전파간섭 검출을 위한 신규 시스템을 추가하지 않고, 기준 운영 시스템, 즉 기준국 수신기의 실시간 원시정보 출력과 RSIM 메시지의 세부 파라미터 정보를 이용하여 전파간섭을 검출할 수 있는 기법 제안과 그 기법을 적용한 전파간섭 모니터링 시스템을 설계하고, 시뮬레이션 결과를 제시한다. 먼저 DGPS 기준국 시스템의 구성과 기능에 대해 설명하고, 무결성 기능의 한계를 제시한다. 또한 전파간섭이 발생했을 경우 기준국 수신기에 미치는 영향에 대해 분석하고, 분석 결과를 기반으로 기준국에 적용할 만한 간이 전파간섭 검출 기법과 이를 기반으로 한 시스템을 설계하여 그 활용 가능성을 제시한다. 성능평가 결과 제안한 기법 및 시스템이 국제해사기구(IMO)에서 요구하는 무결성 성능 중의 하나인 TTA(Time to Alarm) 10초 이내의 성능을 만족할 수 있음을 제시한다.

• The KIPS Transactions:PartA
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• v.13A no.4 s.101
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• pp.335-342
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• 2006

As PRC linear interpolation algorithm is applied after analysed and verified in this paper, the unknown location of a user can be identified by using PRC information of multi-DGPS reference station. The PRC information of each GPS satellite is not varying rapidly, which makes it possible to assume that PRC information of each GPS satellite varies linearly. So, the PRC regeneration algorithm with linear interpolation can be applied to improve the accuracy of finding a user's location by using the various PRC information obtained from multi-DGPS reference station. The desirable PRC is made by the linear combination with the known position of multi-DGPS reference station and PRC values of a satellite using signals from multi-DGPS reference station. The RTK-GPS result was used as the reference. To test the performance of the linearly interpolated PRC regeneration algorithm, multi-channel DGPS beacon receiver was built to get a user's position more exactly by using PRC data of maritime DGPS reference station in RTCM format. At the end of this paper, the result of the quantitative analysis of the developed navigation algorithm performance is presented.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2017.11a
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• pp.188-189
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• 2017

In recent years, the development of GPS navigation system (GNSS), which has been developed not only by US GPS but also by major countries, is entering its final stage. It is time to change the infrastructure and technology system to correct each satellite system. To do this, we analyze the performance of the differential information provided by National Maritime PNT Office for GLONASS currently operating in its normal orbit, and present the its feasibility.

• Journal of Korean Society for Geospatial Information Science
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• v.23 no.4
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• pp.43-48
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• 2015

We studied on pseudo-range correction(PRC) modeling in order to improve differential GNSS(DGNSS) accuracy. The PRC is the range correction information that provides improved location accuracy using DGNSS technique. The digital correction signal is typically broadcast over ground-based transmitters. Sometimes the degradation of the positioning accuracy caused by the loss of PRC signals, radio interference, etc. To prevent the degradation, in this paper, we have designed a PRC model through polynomial curve fitting and evaluated this model. We compared two quantities, estimations of PRC using model parameters and observations from the reference station. In the case of GPS, the average is 0.1m and RMSE is 1.3m. Most of GPS satellites have a bias error of less than ${\pm}1.0m$ and a RMSE within 3.0m. In the case of GLONASS, the average and the RMSE are 0.2m and 2.6m, respectively. Most of satellites have less than ${\pm}2.0m$ for a bias error and less than 3.0m for RMSE. These results show that the estimated value calculated by the model can be used effectively to maintain the accuracy of the user's location. However;it is needed for further work relating to the big difference between the two values at low elevation.

• Journal of Advanced Navigation Technology
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• v.22 no.6
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• pp.602-609
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• 2018

Differential GPS (DGPS) is known as a positioning method using pseudo range correction (PRC) which is communicating between a refence receiver and moving receivers. In real world, a moving receiver loses communication with the reference receiver, resulting in loss of PRC real-time communication. In this paper, we assume that the transmission of the pseudo range correction isinterrupted in the middle of real-time positioning situations, in which calibration information is received in the DGPS method. Under the disconnected communication, we propose 'predict DGPS' that real-time virtual PRC model which is modeled by a machine learning algorithm with previously acquired PRC data from a reference receiver. To verify predict DGPS method, we compared and analyzed positioning solutions acquired from real PRC and the virtual PRC. In addition, we show that positioning using the DGPS prediction method on a real road can provide an improved positioning solution assuming a scenario in which PRC communication was cut off.

• Journal of Advanced Navigation Technology
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• v.21 no.1
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• pp.12-20
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• 2017

A maritime DGPS in Korea offers pseudo-range correction information and monitors integrity of correction data by using multiple GNSS receivers. The maritime DGPS reference station and integrity monitor service sets alarm threshold value about integrity monitoring parameters for preventing service interruption status. However there is no way to avoid system interruption according to malfunction of backup systems and outside factors. Therefore, in this paper, warning threshold values were proposed for maritime DGPS operator can be counteract in advance. And Markov analysis method was carried out for selection of these warning threshold values.

• Journal of Korean Society for Geospatial Information Science
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• v.22 no.1
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• pp.47-54
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• 2014

Precise Point Positioning (PPP) algorithms using GPS code pseudo-range measurements were developed and their accuracy was validated for the purpose of implementing them on a portable device. The group delay, relativistic effect, and satellite-antenna phase center offset models were applied as fundamental corrections for PPP. GPS satellite orbit and clock offsets were taken from the International GNSS Service official products which were interpolated using the best available algorithms. Tropospheric and ionospheric delays were obtained by applying mapping functions to the outputs from scientific GPS data processing software and Global Ionosphere Maps, respectively. When the developed algorithms were tested for four days of data, the horizontal and vertical positioning accuracies were 0.8-1.6 and 1.6-2.2 meters, respectively. This level of performance is comparable to that of Differential GPS, and further improvements and fine-tuning of this suite of PPP algorithms and its implementation at a portable device should be utilized in a variety of surveying and Location-Based Service applications.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.38 no.6
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• pp.521-531
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• 2020

QZSS (Quasi-Zenith Satellite System) provides the CLAS (Centimeter Level Augmentation Service) through the satellite's L6 band. CLAS provides correction messages called C-SSR (Compact - State Space Representation) for GPS (Global Positioning System), Galileo and QZSS. In this study, CLAS messages were received by using the AsteRx4 of Septentrio which is a GPS receiver capable of receiving L6 bands, and the messages were decoded to acquire C-SSR. In addition, Multi-GNSS (Global Navigation Satellite System) Code-PPP (Precise Point Positioning) was developed to compensate for GNSS errors by using C-SSR to pseudo-range measurements of GPS, Galileo and QZSS. And non-linear least squares estimation was used to estimate the three-dimensional position of the receiver and the receiver time errors of the GNSS constellations. To evaluate the accuracy of the algorithms developed, static positioning was performed on TSK2 (Tsukuba), one of the IGS (International GNSS Service) sites, and kinematic positioning was performed while driving around the Ina River in Kawanishi. As a result, for the static positioning, the mean RMSE (Root Mean Square Error) for all data sets was 0.35 m in the horizontal direction ad 0.57 m in the vertical direction. And for the kinematic positioning, the accuracy was approximately 0.82 m in horizontal direction and 3.56 m in vertical direction compared o the RTK-FIX values of VRS.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.11
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• pp.2261-2270
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• 2015

GIS(Geographic Information System) based Positioning technique uses geographic information to predict which satellites are visible or invisible. GPS positioning has poor positioning accuracy in dense urban area where tall buildings block the satellite signals. In this paper, we proposed GIS based Advanced Positioning technique of Mobile GPS to resolve this problem. Particularly, this technique improves positioning accuracy in dense urban area. It is consist of ephemeris and GIS server. We will inversely estimate pseudorange by using NMEA-0183 output data of mobile GPS. After that, we can find more accurate position by using ephemeris and GIS information.