• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.12
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• pp.977-982
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• 2009

Direct numerical simulation (DNS) of a turbulent boundary layer with moderate Reynolds number was performed to scrutinize streamwise-coherence of hairpin packet motions. The Reynolds number based on the momentum thickness (${\theta}_{in}$) and free-stream velocity (U${\infty}$) was varied in the range $Re_{\theta}$=1410${\sim}$2540 which was higher than the previous numerical simulations in the turbulent boundary layer. In order to include the groups of hairpin packets existing in the outer layer, large computational domain was used (more than 50${\delta}_o$, where ${\theta}_o$ is the boundary layer thickness at the inlet in the streamwise domain). Characteristics of packet motions were investigated by using instantaneous flow fields, two-point correlation and conditional average flow fields in xy-plane. The present results showed that a train of hairpin packet motions was propagating coherently along the downstream and these structures induced the very large-scale motions in the turbulent boundary layer.

• Journal of Advanced Navigation Technology
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• v.23 no.6
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• pp.542-547
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• 2019

Autonomous train is investigated to increase the capacity of railroad, and the reliability of wireless communication plays a critical role in terms of decreasing the inter-train distance. In this paper, we propose a transmission scheme for autonomous train communication in highly congested environment. The proposed scheme, namely distributed uplink orthogonal frequency division multiple access (OFDMA) random access (UORA), applies the triggered uplink access (TUA) and the UORA, introduced in the sixth generation WLAN standard, IEEE 802.11ax, for communication devices on vehicle and platform in a distributed manner. The simulation results show that the proposed scheme efficiently improves the packet transmission success rate in highly congested channel conditions compared to the conventional enhanced distributed channel access (EDCA) transmission scheme.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.10
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• pp.1075-1085
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• 2008

Recently, it is studied actively that DVB-S2 for mobility standard(DVB-S2M) is combined with DVB-H, DVB-T and conventional DVB-S2 standard for continuous satellite broadcasting and internet service. Especially, overcoming deep fading by tunnel is main subject. For overcoming deep fading, DVB-S2M proposed cross layer system is consist of upper layer and physical layer. Thus, this paper proposed optimal upper layer coding system fixing the physical layer coding under the simulation results by coding methods, train speed, data rate, interleaver size and IP packet size.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7A
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• pp.550-556
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• 2005

This paper proposes a path prediction-based seamless handover scheme to minimize service disruption and packet loss due to handovers for mobile networks such as Dams. This scheme exploits a peculiar characteristics of trains which move on a predetermined path. The mobile router on the train can predict a handover point and then perform network-layer handover before link-layer handover occurs. This leads to the reduction of handover latency and packet loss during handovers. The performance evaluation showed that the proposed scheme could provide excellent performance, compared with the NEMO basic support scheme.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5C
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• pp.485-497
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• 2009

In this paper, we described DVB-S2 system for mobility. cross layer coding technique are needed to maintain the performance in deep fading channel. Cross layer coding is divided into two kinds of level. First level is Physical layer coding and, second layer is link layer or upper layer coding. Fixed on DVB-S2 short frame coding method as a physical layer, we simulated the various coding method as an upper layer coding. Furthermore, we analyzed the performance of each coding method on according to mobile vehicle speed, data rate, interleaving memory size, and IP packet size.

• Journal of the Semiconductor & Display Technology
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• v.16 no.3
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• pp.65-70
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• 2017

This paper presents the implementation for the master changing algorithm between nodes in a general electric vehicle. The packet processing method based on the unique network method of an electric vehicle is that the method of processing a communication packet has the priority from the node of a vehicle installed at both ends. An important factor in deciding master or slave in a train is that the request data, the status data, and transmits or control codes of sub-devices are controlled from the node which master becomes. If the request data or the status data is transmitted from the non- master side, it is very important that only one of the devices of both stages be master since the data of the request data may collide with each other. This paper proposes an algorithm to select master or slave depending on which vehicle is started first, which node is master or slave, and whether the vehicle key is operation. Finally experimental results show the stable performance and effectiveness of the proposed algorithm.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.6604-6610
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• 2015

In this paper, an efficient Wireless Access in Vehicular Environment (WAVE) packet transmission scheme for railroad communication is proposed. WAVE communication is a wireless local area network (WLAN) based communication and it is developed to be suitable for vehicular communication. There has been a lot of study on WAVE's applicability to Intelligent Transport System (ITS). As one of main transportation methods, by using WAVE, quality of railroad communication including WLAN based Communication Based Train Control (CBTC) can be enhanced and variety of railroad communication systems can be integrated into WAVE. However, there are technical challenges to adopt WAVE in railroad communications. For the simplest single-PHY WAVE, time division alternation of 50ms between Control Channel (CCH) and Service Channel (SCH) is required. Since there are delay sensitive railroad traffic types, alternation operation of CCH and SCH may cause performance degradation. In this paper, after identifying a couple of problems based on detailed analysis, a novel packet transmission scheme under railroad environment is proposed. In order to verify if the proposed scheme meets the requirement of railroad communication, WAVE transmission is mathematically modeled.

• Proceedings of the Korea Contents Association Conference
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• 2010.05a
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• pp.408-410
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• 2010

인터넷에서 단대단 (end-to-end) 가용대역폭 측정은 분산된 응용서비스, 단대단 QoS 보장, 오버레이 네트워크에서의 경로설정, SLA (Service Level Agreements), 분산 네트워크, 지능적인 라우팅 시스템, 비디오/오디오 스트리밍 시스템에서 다양한 연구가 진행되고 있다. 일반적으로 단대단 가용대역폭 측정기법으로 단일-홉-갭 모델에 기반한 패킷 트레인(packet train) 전송을 통하여 가용대역폭을 측정하는 기법과, 각각의 패킷의 전송률을 높여가며 수신측에서의 지연시간(Queueing Delay)를 분석하여 가용대역폭을 측정하는 자가 혼잡 유발(SLoPS : Self-Loading Periodic Stream) 기법이 있다. 본 논문에서는 자가 혼잡 유발 기법을 이용하여 가용대역폭 측정 방안을 제안한다.

• The Journal of the Korea institute of electronic communication sciences
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• v.12 no.5
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• pp.771-776
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• 2017

LTE-R mobile communication technology based on LTE is used to supply various signal and exchange information required for safety operation of train on high speed railway communication system. In this paper, transmission performance of application traffic which is transferred on high speed communication based on LTE-R is analyzed. And some suggestions for application traffic transmission of high speed railway communication will be considered. Computer simulation is used to analyze performance of CBR, VBR as application traffic. Throughput, delay and packet loss rate is used as performance measurement and analysis parameters.

• Structural Monitoring and Maintenance
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• v.6 no.3
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• pp.219-235
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• 2019

Scheduled inspections of common crossings are one of the main cost drivers of railway maintenance. Prognostics and health management (PHM) approach and modern monitoring means offer many possibilities in the optimization of inspections and maintenance. The present paper deals with data driven prognosis of the common crossing remaining useful life (RUL) that is based on an inertial monitoring system. The problem of scheduled inspections system for common crossings is outlined and analysed. The proposed analysis of inertial signals with the maximal overlap discrete wavelet packet transform (MODWPT) and Shannon entropy (SE) estimates enable to extract the spectral features. The relevant features for the acceleration components are selected with application of Lasso (Least absolute shrinkage and selection operator) regularization. The features are fused with time domain information about the longitudinal position of wheels impact and train velocities by multivariate regression. The fused structural health (SH) indicator has a significant correlation to the lifetime of crossing. The RUL prognosis is performed on the linear degradation stochastic model with recursive Bayesian update. Prognosis testing metrics show the promising results for common crossing inspection scheduling improvement.