• Journal of Institute of Control, Robotics and Systems
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• v.18 no.10
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• pp.977-987
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• 2012

One of the most significant errors in the pseudo-range measurement performance of GNSSes (Global Navigation Satellite Systems) is their multipath error for high-precision applications. Several schemes to mitigate this error have been studied. Most of them, however, have been focused on the GPS (Global Positioning System) L1 C/A (Coarse/Acquisition) signal that was designed in the 1970s and is still being used for civil navigation. Recently, several modernized signals that were especially conceived to more significantly mitigate multipath errors have been introduced, such as Time Multiplexed and Composite Binary Offset Carrier (TMBOC and CBOC, respectively) signals. Despite this advantage, however, a problem remains with the use of TMBOC and CBOC modulations: the ambiguity of BOC (Binary Offset Carrier)-modulated signal tracking. In this paper, a novel unambiguous multipath error mitigation scheme for these modernized signals is proposed. The proposed scheme has the same complexity as HRCs (High Resolution Correlators) but with low ambiguity. The simulation results showed that the proposed scheme outperformed or performed at par with the HRC in terms of their multipath error envelopes and running averages in the static and statistical channel models. The ranging error derived by the mean multipath error of the proposed scheme was below 1.8 meters in an urban area in the statistical channel model.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.10
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• pp.2645-2652
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• 1996

In this paper wepropose a sub-block retransmission scheme for ARQ and hybrid ARQ schemes. When the cannel is quiet the sub-block retransmission scheme behaves like a conventional ARQ or hybrid ARQ scheme. As the channel is becoming noisy, the data block is dvided into small sub-blocks for transmission. Each sub-block is encoded for error control by an apprpriate shortened code and the code length of the shortened code is being adaptive to the corresponding channel BER. the reeived block is checked for errors sub-block by sub-block. The propsoed sub-block retransmission scheme provides improved throughput over conventional schemes by retransmitting only the naked sub-blocks in the occurrence of errors. An example of transferring ATM cells is considered for simulation.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.34 no.1
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• pp.21-29
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• 1998

In order to investigate the fish behavior in the water tank, the three dimensional positioning system with two CCD cameras was designed. The positioning system was tested at the vertical circulation water channel with observational part of 1,500L$\times$1,500W$\times$500H mm and the circular water tank with 2,050ø sub(1)$\times$1,850ø sub(2)$\times$400H mm. The observational error of vertical direction was larger than that of horizontal direction, and the observational error became enlarged in all directions according to the increase of depth and distance from the visual axis. The maximum observational errors of horizontal and vertical directions at the circulation channel ranged from -1.7 cm to 1.8 cm (2.4%) and zero to 2.1 cm (4.2%), respectively. But the errors of horizontal and vertical directions at the circular tank ranged from -1.3 cm to 1.3 cm (1.3%) and zero to 1.3 cm (3.3%), respectively.

• Progress in Superconductivity
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• v.4 no.1
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• pp.19-26
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• 2002

We have earlier developed a 40-channel SQUID system. An important figure of merit of a MEG system is the localization error, within which the underlying current source can be localized. With this system, we investigated the localization error in terms of the standard deviation of the coordinates of the ECDs and the systematic error due to inadequate modeling. To do this, we made localization of single current dipoles from tangential components of auditory evoked fields. Equivalent current dipoles (ECD) at N1m peak were estimated based on a locally fitted spherical conductor model. In addition, we made skull phantom and simulation measurements to investigate the contribution of various errors to the localization error. It was found that the background noise was the main source of the errors that could explain the observed standard deviation. Further, the amount of systematic error, when modeling the head with a spherical conductor, was much less than the standard deviation due to the background noise. We also demonstrated the performance of the system by measuring the evoked fields to grammatical violation in sentence comprehension.

• Nuclear Engineering and Technology
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• v.51 no.7
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• pp.1853-1859
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• 2019

The two-thermocouple method was investigated experimentally to evaluate its accuracy for the measurement of local wall temperature and heat flux on a heat transfer tube with an electric heater rod installed in an annulus channel. This work revealed that a thermocouple flush-mounted in a surface groove serves as a good reference method for the accurate measurement of the wall temperature, whereas two thermocouples installed at different depths in the tube wall yield large bias errors in the calculation of local heat flux and wall temperature. These errors result from conductive and convective changes due to the fin effect of the thermocouple sheath. To eliminate the bias errors, we proposed a calibration method based on both the local heat flux and Reynolds number of the cooling water. The calibration method was validated with the measurement of local heat flux and wall temperature against experimental data obtained for single-phase convection and two-phase condensation flows inside the tube. In the manuscript, Section 1 introduces the importance of local heat flux and wall temperature measurement, Section 2 explains the experimental setup, and Section 3 provides the measured data, causes of measurement errors, and the developed calibration method.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.8
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• pp.727-732
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• 2008

In this paper, the state-space representation of generalized complimentary filter is proposed. Complementary filter has the suitable structure to merge information from sensors whose frequency regions are complementary. First, the basic concept and structure of complementary filter is introduced. And then the structure of the generalized filter and its state-space representation are proposed. The state-space representation of complementary filter is able to design the complementary filter by applying modern filtering techniques like Kalman filter and $H_{\infty}$ filter. To show the usability of the proposed state-space representation, the design of Inertial Navigation System(INS) vertical channel damping loop using Global Positioning System(GPS) is described. The proposed GPS/INS damping loop lends the structure of Baro/INS(Barometer/INS) vertical channel damping loop that is an application of complementary filter. GPS altitude error has the non-stationary statistics although GPS offers navigation information which is insensitive to time and place. Therefore, $H_{\infty}$ filtering technique is selected for adding robustness to the loop. First, the state-space representation of GPS/INS damping loop is acquired. And next the weighted $H_{\infty}$ norm proposed in order to suitably consider characteristics of sensor errors is used for getting filter gains. Simulation results show that the proposed filter provides better performance than the conventional vertical channel loop design schemes even when error statistics are unknown.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.11
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• pp.1967-1978
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• 2003

Transparency has been considered as a performance measure in bilateral teleoperation system. Therefore, many issues of transparency have been studied. This paper investigates the transparency in two-channel control architectures. At first, we show the feasibility using analytic transparency-conditions and present the two classes of two-channel control architecture, which are perfectly transparent under ideal situation. In addition, remedies to problems due to impedance model estimation errors under real situation are introduced. They are as fellows; design guideline of control parameters to reduce the effect of model estimation error effect and introduction of time delay estimation for unknown dynamics. From these analyses, the systematic control scheme, which is stable and well transparent under real implementation, is proposed in two-channel control architecture. Finally, the proposed scheme is applied to a 2 D.O.F master-slave system and the experimental results show the validity of the theoretical work.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.10
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• pp.710-718
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• 2010

A numerical study was performed to predict refrigerant charge amount in a mini-channel condenser for a R410A residential air-conditioning system. Multi-channel flat tubes with 12 mini-channels of 1.17 mm average hydraulic diameter for each tube were applied to the condenser. The condenser consisted of 3 passes, and the first, second, and third pass had 44, 19, and 11 tubes, respectively. Each pass was connected by a vertical header. In this study, the condenser was divided into 410 finite volumes, and analyzed by an $\varepsilon$-NTU method. With thermophysical properties and void fraction models for each volume element, the R410A amount distribution and a total charge amount in the condenser were calculated. The predicted total charge amount was compared with the experimentally measured charge amount under a standard ARI A condition. The developed model could predict the charge amount in the mini-channel condenser within prediction errors from -23.9% to -3.0%. Air velocity distribution at the condenser face was considered as non-uniform and uniform by the simulation model, and its results showed that the air velocity distribution could significantly influence the charge amount and vapor phase distribution in the condenser.

• Journal of Environmental Impact Assessment
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• v.18 no.4
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• pp.219-227
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• 2009

Because of urban development and changed land cover types, It is very important to acquire pixel unit of land surface temperature(LST) information when the heat island effect(HIE) of regional area are investigated. The brightness temperature observed by satellite is very useful for assessing the pixel unit of LST distributions for the analysis of thermal environment problems of urban areas. Also, satellite land cover data are very useful to our understanding of surface conditions of study areas. In this study, brightness temperature information of Landsat TM thermal channel was analyzed and compared with land cover information of Jeon-ju city. The atmospheric correction of TM thermal channel carried out to explain for compared LST long term monitoring errors. However, simple estimation and evaluation methods to find a physical relationship between LST from satellite images and in-situ data are compared with reference channel emissivity.

• Journal of the Korean Institute of Telematics and Electronics
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• v.11 no.4
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• pp.9-16
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• 1974

The low channels with frequency range of 54~88MHz and the high channels with frequency range if 174~216 MHz are in use for TV broadcasting in Korea. Since the ratio of the highest frequency to the lowest frequency is 4 to 1, only a logarithmic periodic antenna cou1d cover such an wide frequency range. But, this log-periodic antenna should be big in size. Studies have been done on an antenna of small size with reasonable gain which combines through a channel filter a LPD antenna if low channel with boom length of 2m and a LPD antenna of high channel with boom length of 1.8m. The whole antenna is connected to feeder line through a talun. Experiment shows that the gain of low and high channels is 7 dB and 9 dB respectively, which are lower than theoretical values br nomore than ldB. The difference seemed to come from slight impedance mismatches between antennas and feeder lines, loss in the filter and measurement errors.