• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.14 no.1
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• pp.85-93
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• 2015

Previous studies have estimated crash prediction models with the fixed effect model which assumes the fixed value of coefficients without considering characteristics of each intersections. However the fixed effect model would estimate under estimation of the standard error resulted in over estimation of t-value. In order to overcome these shortcomings, the random effect model can be used with considering heterogeneity of AADT, geometric information and unobserved factors. In this study, data collections from 89 intersections in Daejeon and estimates of crash prediction models were conducted using the random and fixed effect negative binomial regression model for comparison and analysis of two models. As a result of model estimates, AADT, speed limits, number of lanes, exclusive right turn pockets and front traffic signal were found to be significant. For comparing statistical significance of two models, the random effect model could be better statistical significance with -1537.802 of log-likelihood at convergence comparing with -1691.327 for the fixed effect model. Also likelihood ration value was computed as 0.279 for the random effect model and 0.207 for the fixed effect model. This mean that the random effect model can be improved for statistical significance of models comparing with the fixed effect model.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.7
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• pp.605-611
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• 2013

If an accident vehicle propagates emergency messages to other vehicles close to it, the other drivers may realize and avoid the accident spot. In this letter, we propose a broadcast scheme to propagate emergency messages fast in urban VANETs (Vehicular Ad-Hoc Networks) with the help of GPS (Global Position System). In our scheme, a transmitting vehicle chooses the farthest node as the next relay vehicle to propagate emergency messages. And, we suggest an algorithm for intersection recognition and SCF (Store-Carry-Forward) task by taking advantage of periodic hello packets to reduce the propagation time and enhance the delivery ratio.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.403-409
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• 2000

In this paper, we measured and analyzed cross polarization discrimination(XPD), signal correlation coefficient($\rho$) and received signal level decrease, for the application of polarization diversity scheme in the up-link of microcell environments. We experimented in a dense building area, a dense residence area, a market area, a school area and etc at 1.9 GHz. Cross polarization discrimination (XPD) is about 6~11 dB, signal correlation coefficient($\rho$) is below 0.7 and received signal level decrease is smaller than 3 dB. The results of comparing polarization diversity with space diversity show that polarization diversity gain is about 2~5 dB higher in the various area. As a results, polarization diversity scheme is more effective than space diversity scheme in microcell environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.5
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• pp.815-821
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• 1994

Short-term fading in a mobile radio channel is mainly caused by multipath reflected wave by local scatterers or natural obstacles surrounding a mobile unit. In this paper, we analyze probability density function(PDF), level crossing rate(LCR) and widths and depths of fades for the measured field strength data in Seoul and Daejeon areas. As a result, the satatistical distribution of signal variations within any small area with the constant mean value becomes the Rayleigh distribution The variation of fade depths is small regardless of the environment such as urban, suburban. etc. However, the variation of fade widths is large with the change of circumstantial structures and environment. the maximum level crossing rate is obtained near the mean value.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.3 no.2 s.5
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• pp.95-104
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• 2004

This paper describes the design, fabrication, and measurement of a omni-directional beam pattern antenna for base station of the BIS which is one of the ITS services. The antenna is installed on the signal lamp of important crossroad and provides the wireless communication link between vehicles and RSE(Road Side Equipment). The required characteristics of BIS base station antenna are omni-directional beam pattern and specific beam pattern by the road and install environment and installed place of OBU. To get omni-directional beam pattern of antenna, Array configuration and OMA are applied. The measured results of fabricated antenna are as follows; return loss of 640MHz by -10 dB, and a gain of 10.3dBi. It is found that the measured beam patterns are similar to design results.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.20 no.5
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• pp.113-129
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• 2021

Recently, traffic congestion in the city is continuously increasing due to the expansion of the living area centered in the metropolitan area and the concentration of population in large cities. New road construction has become impossible due to the increase in land prices in downtown areas and limited sites, and the importance of efficient data-based road operation is increasingly emerging. For efficient road operation, it is essential to classify appropriate scenarios according to changes in traffic conditions and to operate optimal signals for each scenario. In this study, the Dynamic Time Warping model for cluster analysis of time series data was applied to traffic volume and speed data collected at continuous intersections for optimal scenario classification. We propose a methodology for composing an optimal signal operation scenario by analyzing the characteristics of the scenarios for each data used for classification.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.10 no.3
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• pp.199-205
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• 2017

In a small cell base station used in densely populated areas, a dual polarized multiple antenna(MIMO) is mainly used to increase the cell capacity. This paper demonstrates a dual-polarization antenna with high cross-polarization discrimination(XPD) that can improve the capacity of a small cell using a dual polarization multiple antenna (MIMO). By using the symmetric structure and differential feeding, high XPD in all directions is achieved. In addition, a very similar radiation pattern is observed between each polarization. Because of high XPD and similar radiation pattern in all directions, proposed antenna is well adopted for small-cell multiple-input multiple-output(MIMO) system. Experimental results shows that the proposed antenna has a bandwidth of 180 MHz (2.51~2.7 GHz), a maximum gain of 4.5 dBi (3.5~4.5 dBi), and a half-power beam width of 85 degrees. In addition, average XPD of 26.4 dB in all directions, more than 13.8 dB increase than previous dual-polarization antennas which use single emitter by using different feeding or selectively use polarization through switching.

• Explosives and Blasting
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• v.18 no.2
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• pp.7-13
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• 2000

Abstract The characteristics of bed rock in the study area was classified by means of the crack coefficient estimated from the seismic velocities of in-situ and intact rocks. Various statistical methods were investigated in order to minimize the possible errors in estimating the predictive equation of blasting vibration and to enhance the determination coefficient $R^2$, for more reliable estimation. The determination coefficient showed the highest in the analysis for those groups using weighting function with the number of samples. The analysis for the weighting function employed with standard coefficient and variance also enhanced the determination coefficients significantly compared to the others, but the reliability was slightly lower than results obtained former method. Therefore the most reliable predictive equation of blasting vibration was found to be obtained from a regression analysis of the mean vibration level using the weighting of same distance groups within 15m with the same explosive charge weight per delay. The coefficients, K and n 317.4 and -1.66, respectively, when using the square root scaling, and 209.9 and -1.66, respectively, when using the cube root scaling. The analysis also showed that the square root scaling may be used in the distance less than 31m form the blast source, and the cube root scaling in the distance more than 31m for safe design.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.16 no.5
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• pp.72-84
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• 2017

Together with the Big Data of the 4th Industrial Revolution, the traffic information system has been changed to an section detection system by the point detection system. With DTG(Digital Tachograph) data based on Global Navigation Satellite System, the properties of raw data and data according to processing step were examined. We identified the vehicle trajectory, the link travel time of individual vehicle, and the link average travel time which are generated according to the processing step. In this paper, we proposed a application method for traffic management as characteristics of processing data. We selected the historical data considering the data management status of the center and the availability at the present time. We proposed a method to generate the Travel Time Index with historical link average travel time which can be collected all the time with wide range. We propose a method to monitor the traffic congestion using the Travel Time Index, and analyze the case of intersections when the traffic operation method changed. At the same time, the current situation which makes it difficult to fully utilize DTG data are suggested as limitations.

• Journal of Korean Society of Disaster and Security
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• v.12 no.4
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• pp.1-13
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• 2019

Recently, as the occurrence frequency of sudden floods due to climate change increased, it is necessary to install the facilities that can cope with the initial stormwater. Most researches have been conducted on the design of facilities applying the Low Impact Development (LID) and the reduction effect on rainfall runoff to examine with 1D or 2D numerical models. However, the studies on the examination about flow characteristics and stability of pipe network systems were relatively insufficient in the literature. In this study, the stability of the pipe network system in rainwater storage tank was examined by using 3D numerical model, FLOW-3D. The changes of velocity and dynamic pressure were examined according to the number of rainwater storage tank and compared with the design criteria to derive the optimal design plan for a rainwater storage tank. As a results of numerical simulation with the design values in the previous study, it was confirmed that the velocity became increased as the number of rainwater storage tank increased. And magnitude of the velocity in pipes was formed within the design criteria. However, the velocity in the additional rainwater storage pipe was about 3.44 m/s exceeding the allowable range of the design criteria, when three or more additional rainwater storage tanks were installed. In the case of turbulence intensity and bottom shear stress, the bottom shear stress was larger than the critical shear stress as the additional rainwater storage was increased. So, the deposition of sediment was unlikely to occur, but it should be considered that the floc was formed by the reduction of the turbulence intensity. In addition, the dynamic pressure was also satisfied with the design criteria when the results were compared with the allowable internal pressure of the pipes generally used in the design of rainwater storage tank. Based on these results, it was suitable to install up to two additional rainwater storage tanks because the drainage becomes well when increasing of the number of storage tank and the velocity in the pipe becomes faster to be vulnerable to damage the pipe. However, this study has a assumption about the specifications of the rainwater storage tanks and the inflow of stormwater and has a limitation such that deriving the suitable rainwater storage tank design by simply adding the storage tank. Therefore, the various storage tank types and stormwater inflow scenarios will be asked to derive more efficient design plans in the future.