• Journal of the Korea Institute of Military Science and Technology
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• v.6 no.1
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• pp.59-67
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• 2003

Multipath is an inevitable error source in radio navigation system such as GPS, it causes signal tracking errors such as carrier tracking errors, code tracking errors. Since code tracking error is a dominant error in absolute positioning, this paper focuses on the improvement of code tracking performance. This paper proposes a method that detects the change of autocorrelation function's slope and mitigates the multipath error. Also, this paper shows the performance evaluation results by post-processing the digitized RF samples.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.14 no.2
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• pp.181-188
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• 1996

Geodetic Satellite Positioning Techniques (NNSS, Transit, Doppler, VLBI, SLR etc.) still have much difficulty in surveying and necessity of point positions is being amplified in korea. Therefore some research institutes have being investigated point positioning using the GPS. In this study, 1 arranged the theory deal with point positioning using GPS carrier beat phase of dual frequency and estimated corrections of errors that be included in GPS observable. Also, 1 determined point position by the differencing scheme of GPS carrier phase, and analyzed the accuracy of point position. 1 suggested potentiality of geodetic point positioning using GPS carrier phase by comparing result of relative positioning with result of point positioning and analyzing result of network adjustment fixed any point position.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.37 no.5
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• pp.397-402
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• 2019

Recently, with the emergence of autonomous vehicles and the increasing interest in safety, a variety of research has been being actively conducted to precisely estimate the position of a vehicle by fusing sensors. Previously, researches were conducted to determine the location of moving objects using GNSS (Global Navigation Satellite Systems) and/or IMU (Inertial Measurement Unit). However, precise positioning of a moving vehicle has lately been performed by fusing data obtained from various sensors, such as LiDAR (Light Detection and Ranging), on-board vehicle sensors, and cameras. This study is designed to enhance kinematic vehicle positioning performance by using feature-based recognition. Therefore, an analysis of the required precision of the observations obtained from the images has carried out in this study. Velocity and attitude observations, which are assumed to be obtained from images, were generated by simulation. Various magnitudes of errors were added to the generated velocities and attitudes. By applying these observations to the positioning algorithm, the effects of the additional velocity and attitude information on positioning accuracy in GNSS signal blockages were analyzed based on Kalman filter. The results have shown that yaw information with a precision smaller than 0.5 degrees should be used to improve existing positioning algorithms by more than 10%.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.4
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• pp.251-261
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• 2022

The Centimeter Level Augmentation Service (CLAS) is the Precise Point Positioning (PPP) - Real Time Kinematic (RTK) correction service utilizing the Quasi-Zenith Satellite System (QZSS) L6 (1278.65 MHz) signal to broadcast the Global Navigation Satellite System (GNSS) error corrections. Compact State-Space Representation (CSSR) corrections for mitigating GNSS measurement error sources such as satellite orbit, clock, code and phase biases, tropospheric error, ionospheric error are estimated from the ground segment of QZSS CLAS using the code and carrier-phase measurements collected in the Japan's GNSS Earth Observation Network (GEONET). Since the CLAS service begun on November 1, 2018, users with dedicated receivers can perform cm-level precise positioning using CSSR corrections. In this paper, CLAS-based VRS-RTK performance evaluation was performed using Global Positioning System (GPS) observables collected from the refence station, TSK2, located in Japan. As a result of performing GPS-only RTK positioning using the open-source software CLASLIB and RTKLIB, it took about 15 minutes to resolve the carrier-phase ambiguities, and the RTK fix rate was only about 41%. Also, the Root Mean Squares (RMS) values of position errors (fixed only) are about 4cm horizontally and 7 cm vertically.

• Proceedings of the KSRS Conference
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• 2007.10a
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• pp.90-94
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• 2007

The conventional single-reference station positioning is affected by systematic errors such as ionospheric and tropospheric delay, so that the rover must be located within 10 km from the reference station in order to acquire centimeter-level accuracy. The medium-range real-time kinematic has been proven feasible and can be used for high precision applications. However, the longer of the baseline, the more of the time for resolving the integral ambiguity is required. This is due to the fact that systematic errors can not be eliminated effectively by double-differencing. Recently, network approaches have been proposed to overcome the limitation of the single-reference station positioning. The real-time systematic error modeling can be achieved with the use of GPS network. For expanding the effective range and decreasing the density of the reference stations, Land Survey Bureau, Ministry of the Interior in Taiwan set up a national GPS network. In order to obtain the high precision positioning and provide the multi-goals services, a GPS network including 66 stations already been constructed in Taiwan. The users can download the corrections from the data center via the wireless internet and obtain the centimeter-level accuracy positioning. The service is very useful for surveyors and the high precision coordinates can be obtained real time.

• The KIPS Transactions:PartD
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• v.9D no.1
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• pp.127-134
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• 2002

GPS is one of today's most widely used surveying techniques. But, users can't acquire an enough accuracy in applications of the navigation or geodesy by the GPS positioning technique because of the effects of the ionosphere and troposphere and US DoD's systematic errors. The solution of these restrictions is the DGPS technique that is to eliminate the common errors and can achieve a high accuracy. Although of sufficient density for good DGPS, accuracy of positioning is just not dense enough to provide complete coverage for real-time positioning, because distances between base and rover is short. In this paper, we designed and implemened a RTK-GPS error correction signal transmission system for long-distance using the TCP/IP, which consist of TCP, UDP and IP, which allows a user to increase the distance at which the rover receiver is located from the base, due to radio modem.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.60 no.2
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• pp.152-160
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• 2024

We analyzed risk factors of coastal gillnet fishers during fishing process and considered work safety measures to reduce safety accidents during fishing using a UWB (ultra wideband) based positioning system. The static position accuracy of the UWB based positioning system was 45 cm. When entering a port, there is a risk of falling overboard. When casting a net, there was a risk of falling overboard due to being hit by fishing gear or guards, or getting caught in a buoy line or sinker line. When hauling a net, there is a risk of getting caught between fishing gear and net hauler, and the risk of musculoskeletal disorders due to repetitive work over a long period of time. Most safety accidents during work on fishing boats are blamed on human errors of the fisher and skipper, but safety accidents occur due to a mixture of mechanical and equipment factors, work and environmental factors, and management factors in addition to human errors. Therefore, the 4E were presented as countermeasures against the 4M, which are causes of safety accidents, and the proposed measures were used to identify risk factors for operation process, comply with work safety rules, and ensure the wearing of personal protective equipments. We need to reduce safety accidents during work by making it part of our daily routine. These research results can be used in the future for optimal placement of fishing gear and fishing nets in other coastal industries where safety accidents occur frequently.

• Journal of Positioning, Navigation, and Timing
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• v.1 no.1
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• pp.65-75
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• 2012

We carry out an error analysis of 24-hour global positioning system (GPS)-very long baseline interferometry (VLBI) (GV) hybrid observation data. In this paper, we focus on the impacts of broadcast and final orbits on the GPS delays of the GV hybrid observation by analyzing the residuals, observed - calculated (O-C) values. The residuals show apparent and consistent biases for L1 and L2 signals, respectively. The scatters of the residuals are around a few nanoseconds. The main cause of those observation errors is the absence of the GPS phase and delay calibration system. Most of the satellites show that the differences between the delays, to which broadcast and final orbits are applied, are about 100 times smaller than the current GV hybrid observation errors. We conclude that GPS delays are not greatly affected by orbit accuracies.

• International Journal of Precision Engineering and Manufacturing
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• v.6 no.2
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• pp.55-60
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• 2005

In order to develop the hydrostatic guideways driven by a core less linear motor for ultra precision machine tools, a prototype of guideway is designed and tested. A coreless linear DC motor with a continuous force of 156 N and a laser scale with a resolution of 0.01 ㎛ are used in the system. Experimental analysis on the static stiffness, motion errors, positioning error and its repeatability, micro step response and velocity variation of the guideway are performed. The guideway shows infinite stiffness within 50 N applied load in the feed direction, and by the motion error compensation method using the Active Controlled Capillary, 0.08 ㎛ linear motion error and 0.1 arcsec angular motion error are acquired. The guideway also reveals 0.21 ㎛ positioning error and 0.09 ㎛ repeatability, and it shows stable responses following a 0.01 ㎛ resolution step command. The velocity variation of feeding system is less than 0.6 ％. From these results, it is estimated that the hydrostatic guideway driven by a coreless linear motor is very useful for the ultra precision machine tools.

• MALSORI
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• no.38
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• pp.125-136
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• 1999

This study examined the perception and production of Korean lax, fortis and aspirated stops in three apraxic patients. All of tile subjects made more production errors than perception errors. This indicates that apraxic patients have problems in phonetic execution rather than phonological representation. Additionally, in both production and perception, there were more errors in non-word-initial consonants than in word-initial consonants. These findings contradict those of the previous studies which report more errors in word-initial consonants. This study also found that, unlike previous studies in the types of errors made, distortion errors were high in both non-word-initial and word-initial consonants in apraxic patients. Generally, VOT of the stops showed significant differences among lax, fortis, and aspirated stops, which indicates that there is a failure not in choosing the appropriate stop but in positioning or motor planning at the articulation stage.