• Journal of Positioning, Navigation, and Timing
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• v.13 no.1
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• pp.85-92
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• 2024

This study develops a Global Positioning System (GPS) Code Multipath Grid Map (CMGM) of each individual domestic reference station from the extracted code multipath of measurement data. Multipath corresponds to signal reflection/refraction caused by obstacles around the receiver antenna, and it is a major source of error that cannot be eliminated by differencing. From the receiver-independent exchange format (RINEX) data for two days, the associated code multipath of a satellite tracking arc is extracted. These code multipath data go through bias correction and interpolation to yield the CMGM with respect to the azimuth and elevation angles. The effect of the CMGM on multipath mitigation is then quantitatively analyzed to improve the Root Mean Square (RMS) of averaged pseudo multipath. Furthermore, the single point positioning (SPP) accuracy is analyzed in terms of the RMS of the horizontal and vertical errors. During two weeks in February 2023, the RMSs of the averaged pseudo multipath for five reference stations decreased by about 40% on average after CMGM application. Also, the SPP accuracies increased by about 7% for horizontal errors and about 10% for vertical errors on average after CMGM application. The overall quantitative analysis indicates that the proposed approach will reduce the convergence time of Differential Global Navigation Satellite System (DGNSS), Real-Time Kinematic (RTK), and Precise Point Positioning (PPP)-RTK correction information in real-time to use measurement data whose code multipath is corrected and mitigated by the CMGM.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.8
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• pp.86-94
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• 2009

An idea to improve the performance of error correction with the amplification of input symbol errors is proposed to ease the mismatching problem which occurs in the hardware implementation of the differential analog PRML decoder. The differential analog PRML decoder is the decoder with two blocks of trellis diagram one of which is without branches of "0" and the other one is without the branches of "1". Decoding is performed by comparing the outputs of two blocks. The decoding error is likely to occur when the difference of two outputs is very small and the hardware implementation is not precise due to mismatching. The proposed idea is to increase the discrimination margin for the output "0" and "1" by amplifying the symbol error while the larger path metrics are saturated. To show the performance improvement of decoding with the proposed idea, simulation results are included

• Steel and Composite Structures
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• v.28 no.5
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• pp.589-606
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• 2018

The previous studies reflected the significant effect of neutral-axis position and coupling of in-plane and out-of-plane displacements on behavior of functionally graded (FG) nanobeams. In thin FG beam, this coupling can be eliminated by a proper choice of the reference axis. In shear deformable FG nanobeam, not only this coupling can't be eliminated but also the position of neutral-axis is dependent on through-thickness distribution of shear strain. For the first time, in this paper it is avoided to guess a shear strain shape function and the exact shape function and consequently the exact position of neutral axis for arbitrary gradation of higher order nanobeam are obtained. This paper presents new methodology based on differential transform and collocation methods to solve coupled partial differential equations of motion without any simplifications. Using exact position of neutral axis and higher order beam kinematics as well as satisfying equilibrium equations and traction-free conditions without shear correction factor requirement yields to better results in comparison to the previously published results in literature. The classical rule of mixture and Mori-Tanaka homogenization scheme are considered. The Eringen's nonlocal continuum theory is applied to capture the small scale effects. For the first time, the dependency of exact position of neutral axis on length to thickness ratio is investigated. The effects of small scale, length to thickness ratio, Poisson's ratio, inhomogeneity of materials and various end conditions on vibration and buckling of local and nonlocal FG beams are investigated. Moreover, the effect of axial load on natural frequencies of the first modes is examined. After degeneration of the governing equations, the exact new formulas for homogeneous nanobeams are computed.

• Geophysics and Geophysical Exploration
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• v.12 no.2
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• pp.208-214
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• 2009

Using the GNSS data and tilt-meter data of Boeun (BOEN) and Goesan (GSAN) GNSS stations, we have calculated the differential distance vector variation with the calculation time span set to 1 hour and 3 hour and differential tilt vector variation along time and derived an indicator of similarity between the two variations along time. The similarity such calculated is rather lower than high. But as the existence of a circular type movement of the antenna's phase center's location due to the tilt's variation of the antenna tower because of the sunlight's diurnal change is certain, we recommend to take such diurnal variation of antenna's location into consideration when the correction error in DGNSS or the measured data at reference stations in VRS (Virtual Reference System) is broadcast.

• Journal of Advanced Navigation Technology
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• v.21 no.3
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• pp.279-286
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• 2017

The international maritime organization(IMO) has defined performance requirements for future maritime navigation through IMO resolution A.915(22) in 2001. Many DGPS systems currently providing DGPS services do not meet the performance requirements specified in IMO resolution A.915(22). The use of SBAS is considered as one of the DGPS replacement and supplementary system for coping with the increase in demand performance and providing safe positioning service. In particular, since a large amount of budget is required to rearrange the existing DGPS reference stations, a method which transmits differential corrections generated by using SBAS message has been proposed. In this paper, we compare and analyze the performance of NDGPS which is operated by the National Maritime PNT Office of the ministry of oceans and fisheries(MOF) in Korea and MSAS in Japan. Also, we verify that SBAS, as alternative and complementary system, meets the performance requirement specified in IMO resolution A.915(22).

• Journal of Broadcast Engineering
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• v.25 no.5
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• pp.685-697
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• 2020

Immersive media videos, such as panorama and 360-degree videos, must provide a sense of realism as if the user visited the space in the video, so they should be able to represent the reality of the real world. However, in panorama and 360-degree videos, objects appear to overlap or disappear due to parallax between cameras, and such parallax distortion may interfere with immersion of the user's content. Accordingly, although many video stitching algorithms have been proposed to overcome parallax distortion, parallax distortion still occurs due to the low performance of the Object detection module and limitations of the Seam generation method. Therefore, this paper analyzes the limitations of the existing video stitching technology and proposes a method for detecting and correcting parallax distortion of video stitching using the LDPM (Local Differential Pixel Mean) image evaluation method that overcomes the limitations of the video stitching technique.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.427-429
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• 2013

DGPS Reference Station the national infrastructure generates the DGPS correction information for Differential GPS. Currently, South Korea operates the software based DGPS reference station using the next generation DGPS architecture in order that upgrade the hardware based DGPS reference station. However the software based DGPS reference station proposed by USCG has not changed just a form of its structure but intimate architecture. Accordingly, It can't strengthen the advantages of software based architecture. In this paper, I will propose a new software architecture design that is integrated with DGPS reference station and integrity monitor. This architecture is more simple than existing one so can use the maritime DGPS reference station which is required more simple structure.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.7A
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• pp.569-580
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• 2012

In this paper, an enhanced initial ranging algorithm for large-cell coverage fixed wireless communication system is proposed. In typical wireless communication system such as WiBro, because a round-trip delay between a transmitter and a receiver is within one OFDM (Orthogonal Frequency Division Multiplexing) symbol duration, a frequency-domain differential correlation method is generally used. However, the conventional method cannot be applied due to an increase of a maximum time delay in large-cell system. In case of an accumulative differential method, estimation errors can occur because of frequent sign transitions. In this paper, therefore, we propose an algorithm which can estimate a total timing offset in a ranging channel structure for 15 km cell. The proposed method can improve performance by sign comparison based sign error correction rule between the estimated values and using a weighting scheme based on channel correlation, the number of accumulations, and the noise reduction effect in normalization process. Also, it can estimate the integer timing offset of symbol duration by comparing peak-powers after compensating for the fractional timing offset of symbol duration.

• Journal of the Korean Institute of Intelligent Systems
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• v.23 no.6
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• pp.505-510
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• 2013

In order to detect and identify the GPS clock anomaly in the Differential GPS real environment, this paper addresses a method for minimizing the measurement noise of reference receivers. It estimates the real measurement noise that removed the uncommon error source from pseudorange measurement to minimize the measurement noise. Based on the output of two reference receivers, it first removes the uncommon errors, then optimizes the measurement noise by applying the correction data. Finally, it detects and identifies the satellite clock anomaly using the minimized measurement noise. The method will increase the availability of current DGPS reference system.

• Imaging Science in Dentistry
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• v.35 no.2
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• pp.77-82
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• 2005

Purpose : To reveal what is the distinct differential diagnostic differences between unicystic ameloblastoma and solid or multicystic ameloblastoma. Materials and Methods : 56 cases of ameloblastoma were retrospectively reviewed and evaluated among the patients who had taken CT scans at the department of Oral & Maxillofacial Radiology in Yonsei University Dental Hospital from January 1996 to December 2003. Results : In 56 cases, 21 cases $(37.5\%)$ were unicystic ameloblastoma, 35 cases $(62.5\%)$ were solid or multicystic ameloblastoma. Only 1 case $(4.8\%)$ of unicystic ameloblastoma and 4 cases $(11.4\%)$ of solid or multicystic ameloblastoma were occurred in maxilla. 13 cases $(61.9\%)$ of unicystic ameloblastoma were observed as unilocular, and 8 cases $(38.1\%)$ as lobulated. 5 cases $(14.3\%)$ of solid or multicystic ameloblastoma were observed as unilocular, 13 cases $(37.1\%)$ as lobulated, and 17 cases $(48.6\%)$ as multilocular. Tn the results from the measurements after correction of the buccolingual widths and heights to the mesiodistal lengths, there is a statistically significant difference between unicystic ameloblastoma and solid or multicystic ameloblastoma in ANCOVA test (p<0.05). Hounsfield units in the lesion were $24.9{\pm}8.8\;HU$ in unicystic ameloblastoma, $31.2{\pm}11.5\;HU$ in solid or multicystic ameloblastoma. There is no statistically significant difference (p>0.05). Conclusion : Characteristic differences between unicystic ameloblastoma and solid or multicystic ameloblastoma is that there is higher prevalence of solid or multicystic ameloblastoma that have lobulated or multilocular patterns. To measure the Hounsfield units in the lesion is helpful, but it is not a differential diagnostic point between unicystic ameloblastoma and solid or multicystic ameloblastoma.