• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.21-26
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• 2006

This paper focuses on modeling and predicting differential GPS corrections transmitted by marine radio-beacon systems using artificial neural networks. Various neural network structures with various training algorithms were examined, including Linear, Radial Biases, and Feedforward. Matlab Neural Network toolbox is used for this purpose. Data sets used in building the model are the transmitted pseudorange corrections and broadcast navigation message. Model design is passed through several stages, namely data collection, preprocessing, model building, and finally model validation. It is found that feedforward neural network with automated regularization is the most suitable for our data. In training the neural network, different approaches are used to take advantage of the pseudorange corrections history while taking into account the required time for prediction and storage limitations. Three data structures are considered in training the neural network, namely all round, compound, and average. Of the various data structures examined, it is found that the average data structure is the most suitable. It is shown that the developed model is capable of predicting the differential correction with an accuracy level comparable to that of beacon-transmitted real-time DGPS correction.

• Journal of Astronomy and Space Sciences
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• v.26 no.1
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• pp.59-74
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• 2009

Relative navigation system is presented using GPS measurements from a single-channel global positioning system (GPS) simulator. The objective of this study is to provide the real-time inter-satellite relative positions as well as absolute positions for two formation flying satellites in low earth orbit. To improve the navigation performance, the absolute states are estimated using ion-free GRAPHIC (group and phase ionospheric correction) pseudo-ranges and the relative states are determined using double differential carrier-phase data and singled-differential C/A code data based on the extended Kalman filter and the unscented Kalman filter. Furthermore, pseudo-relative dynamic model and modified relative measurement model are developed. This modified EKF method prevents non-linearity of the measurement model from degrading precision by applying linearization about absolute navigation solutions not about the priori estimates. The LAMBDA method also has been used to improve the relative navigation performance by fixing ambiguities to integers for precise relative navigation. The software-based simulation has been performed and the steady state accuracies of 1 m and 6 mm ($1{\sigma}$ of 3-dimensional difference errors) are achieved for the absolute and relative navigation using EKF for a short baseline leader/follower formation. In addition, the navigation performances are compared for the EKF and the UKF for 10 hours simulation, and relative position errors are mm-level for the two filters showing the similar trends.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.1125-1129
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• 2005

In this study, for suggesting the development of GPS navigation in the naval vessels, the test of GPS error is conducted for analyzing the precision of GPS installed in the naval vessels. And the reliability and utilization of GPS are verified throughout interview and questionnaire with the workers in the naval vessels.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.946-947
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• 2016

This paper is for analyzing not only DGNSS navigation signal but also the navigation parameter of MSAS. The sufficient navigation satellites to determine 3-D position based on DGNSS are simultaneously available at MSAS monitering station and the test region of Korean peninsula. It was verified that the carrier to noise signal is stable to maintain the reliable positioning.

• Journal of the Korean Association of Geographic Information Studies
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• v.15 no.4
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• pp.151-161
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• 2012

The purpose of this study was to build a web-server for culture heritages management information system in order to efficiently manage and safely preserve undesignated cultural properties in the Namsan area in Kyeongju, which have been neglected so far. In order to achieve this purpose, data were collected on the basis of undesignated cultural properties in the study area. To acquire the location and range GPS were used and spatial data including geographic coordinates, visual materials and structured interviews were conducted through field survey. In addition, in order to obtained reliable and accurate locations of undesignated cultural properties which are scattered, DGPS(Differential Global Positioning System) were used. The spatial database was constructed based on the standard of cultural properties and attribute data was linked to geo-spatial information(digital map and aerial photographs). This system was built in a web-server environment. The result shows detailed description on the selected output for selected location and property information can be located on the map. In particular, a database to search for the status and modification of cultural properties will provide information to the users.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.5
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• pp.425-433
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• 2002

After the removal of SA (Selective Availability), horizontal accuracy of 25m(2dRMS) is easily obtained using GPS (Global Positioning System). In this paper, the error characteristics without SA are analyzed and a navigation algorithm concerns this error characteristics is proposed to further improve the accuracy. The proposed method utilizes the relationship between elevation angle and errors that are remained after ionospheric and troposheric delay compensation. The relationship is derived from real measurements and used as a weighting matrix of weighted least squares estimator. Furthermore, a RAIM (Receiver Autonomous Integrity Monitoring) technique is included to remove abnormal measurements affected by multi-path or low SNR (Signal-to-Noise Ratio). It is shown that using the proposed method, more than 4 times accurate result, which is comparable with DGPS (Differential GPS), can be obtained from experiments with real data. Besides accuracy and reliability, the proposed method reduces large jumps in position and maintains better performance than a method using mask angle to completely remove satellites below this mask angle. Thus it is expected that the proposed method can be efficiently applied to land navigation where some satellites are blocked by building or forest.

• Journal of the Korean Society for Marine Environment & Energy
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• v.8 no.1
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• pp.17-22
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• 2005

The movement of drifting ships on the sea is closely related to marine environmental forces such as waves, currents, winds, etc. To develop a prediction model for trajectories oi drifting ships, an experiment on the movement of drifting ships was carried out in the Southeastern Sea of Korea. Five types of ships including a lire raft and tour ships with G/T 10tons, G/T 2o tons, G/T 50 tons, and G/T 80 tons, were considered in the experiment. The G/T 50 ton class ship was used as a base ship for obtaining the currents, winds and heading angles of ship following the trajectory. The trajectory of each ship was measured by DGPS(Differential Global Positioning System) and collected using APRS(Automatic Position Reporting System) installed on the base ship. The error range in position fix of DGPS are approximately ±1 m. The drift speed of ship in the experiment was between 3％ to 5％ of wind speed and drift direction of ship was deflected by ±90° from wind direction. Also, the heading of drifting ship was normal to wind direction.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2004.04a
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• pp.275-278
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• 2004

The geo-referencing of satellite imagery is a key task in remote sensing. GCPs are points the position of which is known both in the image and in the supporting maps. Mapping function makes the determination of map coordinates of all image pixels possible. Generally manual operations are done to identify image points corresponding to the points on a digital topographic map. In order to accurately measure ground coordinates of GCPs, differential global positioning system (DGPS) surveying are used. To acquire the sufficient number of well distributed GCPs is one of the most time-consuming and cost-consuming tasks. This paper describes the procedure of automatically extracting GCOs using GCP database. GCP image chips and image matching technique are used for automatic extraction of GCPs. We developed image processing tool for making image chip GCPs and Web Server for management of GCPs.

• Journal of Biosystems Engineering
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• v.23 no.1
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• pp.75-82
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• 1998

Autonomous speedsprayer operation was conducted using a fuzzy controller combined with a DGPS. The signal of DGPS receiver and signals of four ultrasonic sensors were processed in real time. The speedsprayer was steered with two levers controlled by two hydraulic cylinders. The fuzzy controller has two inputs; direction of running obtained from the DGPS receiver and distance from trees measured by ultrasonic sensors. The operation times of the hydraulic cylinders were inferred as outputs of the fuzzy controller. Field test results showed that the speedsprayer could be autonomously operated by the developed fuzzy controller including turning operation in the end of the tree row. The ultrasonic sensors contributed a little to performance of the autonomous operation, but the speedsprayer could avoid trees or obstacles in emergent situations with them.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.127-128
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• 2006

The proposed differential LC cross-coupled VCO is implemented in InGap/GaAs HBT process for an adaptive Global Positioning system(GPS) application. Two filtering capacitors are used at the base of output buffer amplifiers at the both sides of the core m order to improve phase noise characteristics. The VCO produced a phase noise of -133 dBc/Hz at 3MHz offset frequency from the carrier frequency of 1.489GHz and the second harmonic suppression is significantly suppresed up to -49dBc/Hz in simulation result. The three pairs of BC diodes are integrated m the tank circuit to increase the VCO Tunning range.