• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.28 no.1
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• pp.65-72
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• 2010

In this study, the performances of a medium grade IMU which is aimed for Mobile Mapping System and a low grade IMU for pedestrian navigation are analyzed through simulations under GPS signal blockage. In addition, an analysis on the accuracy improvement of barometer, electronic compass, or multi-sensor(combination of barometer and electronic compass) to correct medium grade or low grade IMU errors in the situation of GPS signal blockage is performed. With the medium grade IMU, the three dimensional positioning error from INS exceeds the demanded accuracy of 5m when the block time is over 30 seconds. When we correct IMU with barometer, compass, or multi-sensor, however, the demanded accuracy is maintained up to 60 seconds. In addition, barometer is more effective than the electronic compass when they are combined. In case of low grade IMU like MEMS IMU, the three dimensional positioning error from INS exceeds the demanded accuracy of 20m when the block time is over 15 seconds. When we correct INS with barometer, compass, or multi-sensor, however, the demanded accuracy is maintained up to 15 seconds in simulation results. On the contrary to medium grade IMU, electronic compass is more effective than the barometer in case of low velocity such as pedestrian navigation. It is expected that the analysis suggested a method to decrease position or attitude error using aided sensor integration when MMS or pedestrian navigation is operated under 1he environment of GPS signal blockage.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.5
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• pp.493-504
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• 2008

Space-Based Augmentation System (SBAS), which is one of the GPS augmentation systems, is a Wide-Area Differential GPS that provides differential GPS corrections and integrity data. In this study, we did performance analysis of kinematic SBAS surveying by conducting Real-Time Kinematic (RTK), DGPS, standalone, and SBAS surveys. Considering static survey results as truth, 2-D Root Mean Square (RMS) error and 3-D RMS error were computed to evaluate the positioning accuracy of each survey method. As a result, the 3-D positioning error of RTK was 13.1cm, DGPS 126.0cm, standalone (L1/L2) 135.7cm, standalone (C/A) 428.9cm, and SBAS 109.2cm. The results showed that the positioning accuracy of SBAS was comparable to that of DGPS.

• Spatial Information Research
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• v.10 no.3
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• pp.407-419
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• 2002

In this study, the design of 4S-Van system is discussed fur the implementation of laser mapping system. Laser device is fast and accurate sensor that acquires 3D road and surface data. The orientation laser sensor is determined by loosely coupled (D)GPS/INS Integration. Considering current system architecture, (D)GPS/INS integration is performed far performance analysis of direct georeferencing and self-calibration is performed for interior and exterior orientation and displacement. We utilized 3 laser sensors for compensation and performance improvement. 3D surface data from laser scanner and texture image from CCD camera can be used to implement 3D visualization.

• Journal of Advanced Navigation Technology
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• v.11 no.4
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• pp.371-377
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• 2007

Ionospheric time delay is one of the main error source for single-frequency DGPS applications, including time transfer and Wide Area Differential GPS (WADGPS). Grid-based algorithm was already developed for WADGPS but that algorithm is not applicable to geomagnetic storm condition in accuracy and management. In geomagnetic storm condition, the spatial distribution of vertical ionospheric delay is noisy and therefore the accuracy of modeling become low in grid-based algorithm. For better accuracy, function based algorithm can be used but the continuity of correction message is not guranteed. In this paper, we propose the ionospheric model using wavelet based algorithm. This algorithm shows better accuracy with the same number of correction message than the existing spherical harmonics algorithm and guarantees the continuity of correction messages when the number of message is expanded for geomagnetic storm condition.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2011.06a
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• pp.323-325
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• 2011

광역보정시스템은 기존의 NDGPS 방식과 달리 GPS 측정치 오차를 기준국을 기준으로 스칼라량으로 계산하지 않고, 전리층 지연 오차의 경우 전리층 분포 맵을 생성하고 위성관련오차의 경우 4차원(x, y, z, t) 보정정보를 생성하게 된다. 이러한 특성으로 인해 광역보정시스템은 기존의 NDGPS 방식보다 적은 수의 기준국으로 보다 넓은 지역을 커버할 수 있고 광역보정사용자는 기준국과의 거리와 관계 없이 균일하고 우수한 수준의 보정정보 및 무결성 정보를 제공받을 수 있게 된다. 본 논문에서는 광역보정시스템 구축에 필요한 핵심 기술 중 하나인 전리층 지연 오차 추정 알고리듬에 대해 설명하였다. 기준국 측정치를 이용해 전리층 분포 맵을 생성하기 위해 핵심적인 단계인 위성 및 기준국 수신기 IFB(Inter-Frequency Bias) 제거 방법에 대해서 설명하고 격자 알고리듬을 활용한 전리층 맵 생성방법에 대해서 설명하고 그 결과를 시뮬레이션을 통해 확인하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.10
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• pp.2195-2202
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• 2011

Recently, navigation system is used to inform users of vehicle location and driving direction, moving distance and so on. This navigation uses GPS sensor for current location determination. The GPS sensor will determinate current coordinates by using triangulation algorithm. This characteristic bring about that the GPS signal is not available in the shadow region such as tunnel and urban canyon. Moreover, Even though the signal is available, inherent positional error rate of the GPS often results in the dislocation of vehicle. To solve, these problems, a new positioning system is proposed in the paper. The System utilizes geomagnetic sensors of smartphone, speed information of CAN of vehicle though bluetooth and WiFi APs for GPS shadow area. The experimental test shadows that the proposed system using multiple data is able to determine the position of vehicle in GPS shadow areas.

• Journal of Advanced Navigation Technology
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• v.7 no.2
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• pp.156-161
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• 2003

In this study, a hybrid navigation system with a low-cost GPS Receiver plus Gyro and Odometer is developed and tested. This hybrid navigation system adopted a modified coupling method which can be distinguished from tightly coupled method or loosely coupled method, so that GPS receivers or Gyros or Odometers can be chosen arbitrary. Comparing to the existing hybrid navigation system, the test results show that this navigation system enhances the accuracy and is robust against the multipath error. It is also proven that this system has an advantage of acquiring GIS data for post processing.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.10a
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• pp.593-599
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• 2007

PC based DVR replaces existing analog CCTV system therefore expands the field and DVR is used for monitoring and security so it requires exact time(clock). But DVR system can't maintains exact clock causing several reasons. For providing exact time information we should use additional system. For economical and usable environment, using GPS system is most suitable suggested solution than use WAN(Wide Area Network). Therefore in this paper for analysis the result of PC based DVR's system clock using GPS system, 1) clock source receiving module that receives the clock form GPS satellite and 2) GPSW H/W units that provide clock source to PC Based DVR 3)Daemon software named PCSW which adjust PC's clock so system could reduced the clock difference with UTC clock and measured the result.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.10
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• pp.2285-2291
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• 2015

At present, available positioning satellites are not only the GPS, but also GLONASS, GALILEO, QZSS, BeiDou. However, the differential GPS, the augmentation service for increase the positioning accuracy, is follow the RTCM version 2.3 standard. So, it can service the correction information about only GPS. For solve this problem, RTCM is making the new version of RTCM message standard that can service the correction information for all of available GNSS. In South Korea, the software DGNSS RSIM system was installed at almost the whole DGNSS reference station. In this reason, that can cope with the new RTCM version 2.4 quickly. However, the DGNSS Reference Station based RSIM 1.3 can not make the GNSS's PRC simultaneously and can not support RTCM version 2.4. Thus, in this paper, the version of RTCM 2.4 is analyzed and the RTCM version 2.4 message generating module's architecture for software DGNSS reference station is designed.

• Journal of Astronomy and Space Sciences
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• v.18 no.1
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• pp.63-70
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• 2001

IDGPS(Inverted Differential Global Positioning System) is one of technique improving the accuracy of GPS positioning and is mostly used for tracking an automatic vehicle. In the IDGPS, the user send it’s GPS position and related satellite information to dispatcher, and the corrections are made at the dispatcher to get corrected user position. IDGPS suffered correction degradation as the baseline become large. This problem is resolved using NIDGPS(Network IDGPS). As the experimental results are demonstrated, the improvement of position accuracy using IDGPS and NIDGPS is verified.