• Journal of Korean Society for Geospatial Information Science
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• v.4 no.2 s.8
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• pp.15-22
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• 1996

As the exact geographical information has been nowadays required for effective developing and using of national land, in the country, there has been interested in using of GPS, and its practical use is expected. Various kinds of fundamental research for practical use of GPS is being accomplished. In this study, a test was carried out over 9 stations with baseline of the range of 1.5 to 210km, and the accuracy of baseline length by GPS relative positioning was variously considered. As result of this study, using a GPS receiving L1 frequency only, baseline accuracy for 2 hour observation was of the order of 0.3ppm for the 10km, and for I hour was below 1ppm. Using a GPS receiving dual frequency(L1/L2), baseline accuracy was of the order of 0.3ppm for the 100km to 200km as 3 hour observation using double difference methods by carrier phase. With basic on the result of this study, when observation and baseline processing are proceeded by the selected optimum observation time and using of baseline processing method, we can expect that geographical information will be acquired effectively.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.19 no.4
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• pp.317-325
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• 2001

Although GPS has proven to be efficient in the fields of navigation and surveying, it has many problems of positioning in downtown areas. Therefore, if GPS is combined with GLONASS which is similar to GPS in its positioning and signal system, it is expected that accuracy will be improved. However, we should address certain problems that exist related to the coordinate, time, and signal system between the two. The purpose of this study is to develop a GPS/GLONASS combination program by considering the properties of GPS and GLONASS and to solve the problems related to differences in the coordinates system and signal system. It is also to present the efficiency of the program in navigation and geographic information through analyzing 3D positioning accuracy by GPS/GLONASS combination with an application experiment. As a result of this study, the accuracy of the DGPS/DGLONASS positioning program corresponded to that of commercial program, and that's accuracy was better than that of DGPS. Especially, the acquisition of navigation and geographic information was possible by DGPS/DGLONASS combination in downtown area where the continuous 3D positioning is impossible by DGPS only.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.4
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• pp.245-254
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• 2018

Impact of tropospheric correction techniques on accuracy of the GPS (Global Positioning System) derived ellipsoidal heights has been experimentally assessed in this paper. To this end, 247 baselines were constructed from a total of 88 CORS (Continuously Operating Reference Stations) in Korea. The GPS measurements for seven days, acquired from the so-called integrated GNSS (Global Navigation Satellite Systems) data center via internet connection, have been processed by two baseline processing software packages with an application of the empirical models, such as Hopfield, modified Hopfield and Saastamoinen, and the estimation techniques based on the DD (Double-Differenced) measurements and the PPP (Precise Point Positioning) technique; hence a total number of the baseline processed and tested was 8,645. Accuracy and precision of the estimated heights from the various correction schemes were analyzed about baseline lengths and height differences of the testing baselines. Details of these results are summarized with a view to hopefully providing an overall guideline of a suitable selection of the modeling scheme with respect to processing conditions, such as the baseline length and the height differences.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.6
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• pp.267-275
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• 2013

EKF has been widely used for GPS/INS integration as standard method but EKF has one well-known drawback. if the errors are not within the bounded region, the filter may be divergent. The particle filter has the advantage of the nonlinear and non-gaussian system. This paper proposes a method for compensating the GPS position errors based on the particle filter and presents loosely-coupled GPS/INS integration using proposed algorithm. We used GPS position pattern with particle filter and added attitude kalman filter for improving attitude accuracy. To verify the performance, the proposed method is compared with high cost GPS as reference. In the experimental result, we verified that the accuracy and robust were well improved by the proposed method filter effectively and robustness than by original loosely-coupled integration when vehicle turns at corner.

• Journal of Satellite, Information and Communications
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• v.6 no.1
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• pp.68-74
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• 2011

In this paper, we present the enhancement results such as availability and accuracy using the GPS L1 and Galileo E1 signal combination. To enhance the acquisition and tracking performance of signal processing in GNSS receiver. several tracking loops with integrator, discriminator, and loop filter module are applied. Also, this paper presents the performance comparison results between prototype receiver equipped with hardware board and software receiver. Also the tracking loop performance of real hardware receiver is verified by comparing with tracking accuracy, sensitivity occurred by the Spirent simulator. Especially, to process the Galileo E1 signal, it is used the a power early late type which is the typical type for DLL discriminator.

• Korean Journal of Geomatics
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• v.3 no.2
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• pp.129-140
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• 2004

This paper addresses solutions th the challenges of carrier phase integer ambiguity resolution and cycle slip detection/identification, for maintaining high accuracy of an integrated GPS/Pseudolite/INS system. Such a hybrid positioning and navigation system is an augmentation of standard GPS/INS systems in localized areas. To achieve the goal of high accuracy, the carrier phase measurements with correctly estimated integer ambiguities must be utilized to update the system integration filter's states. The contribution presents an effective approach to increase the reliability and speed of integer ambiguity resolution through using pseudolite and INS measurements, with special emphasis on reducing the ambiguity search space. In addition, an algorithm which can effectively detect and correct the cycle slips is described as well. The algorithm utilizes additional position information provided by the INS, and applies a statistical technique known as th cumulative-sun (CUSUM) test that is very sensitive to abrupt changes of mean values. Results of simulation studies and field tests indicate that the algorithms are performed pretty well, so that the accuracy and performance of the integrated system can be maintained, even if cycle slips exist in the raw GPS measurements.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.4
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• pp.659-665
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• 2016

In this paper, we propose a novel position accuracy enhancement method of a low-end GPS using digital map information. The latest digital map has various kinds of information on geographical features. The proposed method uses position information of lane marks among the geographical features. We define the position information of lane marks as the reference points. The position information of a low-end GPS acquired for a period of time is defined as the source points. In the proposed method, rotation and translation matrices between the reference and the source points are calculated by using an Iterative Closest Point(ICP) algorithm. The source points are transformed by the obtained rotation and translation matrices. Finally, the transformed source points are projected on the reference points. Through these processes, the position accuracy of a low-end GPS is ultimately enhanced. To verify the proposed method, the various real experimental results are presented.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.17 no.3
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• pp.283-292
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• 1999

Aerotriangulation for the large scale mapping(photo-scale l/5,000) was studied with the projection center determined by kinematic DGPS positioning. For the feasibility study, the accuracy and error was analyzed with the comparison between a projection center from the conventional model adjustment and the projection center determined by the kinematic DGPS positioning. Kinematic DGPS-supported Bundle adjustment was also performed. The accuracy of projection center, determined by L1 phase data observed within 30 km from base station, was stable, and the planimetric accuracy(RMS) is 13 cm and the vertical accuracy(RMS) is 15 cm with 4 ground control points, which satisfies the national standard of digital mapping. Thus, this study shows that GPS-assisted aerotriangulation can be used for economic digital mapping.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.1
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• pp.39-47
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• 2008

Automatic landing performance of UAV can be enhanced by adding Pseudolite(PL) to GPS. However, it is very hard to install and operate PL with confidence because GPS satellites are moving and the landing zone are usually changeable. The coverage and accuracy of combined GPS and PL can be estimated by using simulator and the correct information is very crucial to UAV operation. In this paper, design, implementation and evaluation of GPS/PL simulator for UAV landing are given. A very realistic coverage estimation is obtained using GIS data and ray launching method with considerations of the transmitter power level, altitude of UAV, number and location of PL. The expected accuracy is estimated using DOP and NSP computed using both GPS and PL. The performance of simulator is evaluated by comparing with the results of a real GPS receiver, and the certified simulator shows the required accuracy for UAV landing can be easily met by proper installation of at least 2 PLs.

• Journal of Navigation and Port Research
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• v.36 no.6
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• pp.429-435
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• 2012

Although GNSS hardware and software technologies have been steadily advanced, it is still difficult to obtain reliable positioning results in the area with lots of signal blockage. In this study, algorithms for integrated GPS and GLONASS double difference relative positioning were developed and its performance was validated via simulations of signal blockages. We assumed that signal blockages are caused by high-rise buildings to the east, west, and south directions. And then, GPS-only and integrated GPS/GLONASS positioning accuracy was analysed in terms of 2-dimensional positioning accuracies. Compared with GPS-only positioning, the positioning accuracy of integrated GPS/GLONASS improved by 0.3-13.5 meters.