• Journal of KIISE:Information Networking
• /
• v.32 no.4
• /
• pp.495-507
• /
• 2005

Measuring the end-to-end available bandwidth in the Internet is a useful tool for distributedapplication services or QoS (Quality-of-Service) guarantee. To measure the end-to-end available bandwidth, Single-hop Gap model-based packet train measurement techniques are well-known. However, the error of packet train output gap can happen by network topologies. This error of the output gap causes the inaccuracy of the available bandwidth measurement. In this paper, we propose a new end-to-end available bandwidth measurement technique with accurate capacity measurement and fast convergence methods. To solve the erroneous capacity measurement problem of the back-to-back packet train transmission, we propose a new available bandwidth measurement method by decoupling the capacity measurement with the initial gap of the packet train. Also, we propose a new technique to predict the proper initial gap of the packet train for faster convergence. We evaluate our proposed method by the simulation in various topologies comparing with previous methods.

• Proceedings of the KSR Conference
• /
• 2006.11b
• /
• pp.1454-1460
• /
• 2006

This paper assesses communication performance using a roaming simulator when roaming occurs between onboard and ground wireless communication devices for communication based train control system (CBTC). Generally, CBTC is defined as the system regularly collecting location and speed data from each train, transmitting distance information to a train, and optimizing train speed according to train performance. When a train is moving, roaming is also performed to continuously transmit and receive train control information between the ground controller and the train. To operate CBTC, packet loss rate should be less than 1%, roaming time less than 100ms during roaming. We developed a roaming simulator to check communication performance before installing ground and onboard equipments on actual wireless sections. The roaming simulator to be introduced in this paper is for roaming simulation before conducting CBTC field test, which is the project to develop Urban Rail Signaling System Standards, being conducted in KRRI. The simulation consists of one onboard wireless communication device and three ground wireless communication devices, and the roaming simulator estimate packet loss rate occurring during roaming process of the two devices. Therefore, if you use the roaming simulator before the field test, you can predict various problems to occur in actual environment and reduce time, cost and people necessary to resolve these problems.

• Journal of the Korean Society for Railway
• /
• v.17 no.6
• /
• pp.402-409
• /
• 2014

Wireless local area network (WLAN) is a widely used wireless access method due to its easy usability and excellent performance. However, its performance degrades significantly as the number of users increases. In busy train stations, where the number of WLAN users are large and, more importantly the number of simultaneous packet transmission attempts is extremely large due to the time synchronization upon train arrival, the packet transmission delay problem is very severe and almost impossible for WLAN stations to initiate communication with WLAN networks. In this paper, a novel distributed WLAN access scheme for efficient WLAN communication in busy train stations is proposed. Using the proposed scheme, WLAN access delay can be significantly reduced under highly congested traffic environments. Therefore, a significant performance enhancement for the WLAN performance used in the Communication Based Train Control (CBTC) can be achieved.

• Journal of the Korean Society for Railway
• /
• v.10 no.6
• /
• pp.758-765
• /
• 2007

In this paper, we propose an efficient seamless handoff scheme to minimize packet loss and unnecessary packets on the Internet using the peculiar mobility characteristics of public vehicles such as trains. MR (Mobile Router) in a train visits each AR (Access Router) in the fixed order. As the MR detects reachability to the NAR (Next Access Router) on the new link, the PAR (Previous Access Router) can directly deliver packets from MR's HA (Home Agent) to the NAR according to the HML (Handoff Mobile router List). Then. the NAR buffers them until the MR finishes L3 (Layer 3) handoff procedure with the NAR. Therefore, our scheme can support a seamless handoff without the packet loss and unnecessary packets on the Internet. The result of our performance evaluation has shown that the proposed scheme could provide excellent performance, compared with the NEMO basic support protocol and the Bi-casting protocol.

• Korean Journal of Mathematics
• /
• v.17 no.4
• /
• pp.399-409
• /
• 2009

We study the weak convergence of various models to Fractional Brownian motion. First, we consider arima process and ON/OFF source model which allows for long packet trains and long inter-train distances. Finally, we figure out power spectrum density as a Fourier transform of autocorrelation function of arima model and binary signal model.

• Korean Journal of Mathematics
• /
• v.15 no.1
• /
• pp.71-78
• /
• 2007

We consider arrival process and ON/OFF source model which allows for long packet trains and long inter-train distances. We prove the weak convergence of theses processes to Fractional Brownian motion. Finally, we figure out the coefficients of $B_H(t)$ and time $t$ when ON/OFF periods have the Pareto distribution.

• Journal of the Semiconductor & Display Technology
• /
• v.15 no.4
• /
• pp.61-66
• /
• 2016

This paper presents the implementation for a network structure of railway cars using a point to point communication. Most of network's representative specifications for a train are the FIP (Field Bus), MVB (Multifunction Vehicle Bus), CAN and WTB (Wire Train Bus) which is used by ALSOM, SIEMENS and BOMBADIER as major in this field. These networks in a physical layer use a multi-drop method, connected from $1^{st}$ car to $n^{th}$ car of a train through a cable without any extra services such as an electric part, amplifier. However waveforms which is passed through a long cable in the multi-drop are distorted by a capacitance or resistance of the cable or environments. Also since using a cable connected directly from $1^{st}$ car to $n^{th}$ car, if over two trains make double head, it isn't easy to distinguish ID for each railway cars. So by using the point to point network per each car, it is able to reduce a distortion. Also since reducing distortion, this communication speed can be been higher and transmit and receive any packets more stably. Using proposed token in a packet, this can make ID per each railway car automatically. Finally experimental results show the good performance and effectiveness of the proposed method.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.20 no.3
• /
• pp.31-36
• /
• 2020

The LTE-R system is a system consisting of a packet network that provides all IP-based services. Continuous failures related to the platform safety gate and subsequent safety accidents related to passengers and safety gate workers continue. The secondary damage caused by the failure of the platform safety door and the related human life damage have emerged as a major social issue.. By linking the beacon system to the Long Term Evoluton-Railway (LTE-R) network, an LTE-based railway wireless network currently in operation or being installed, it precisely locates trains and provides standardized fault alerts to train crews. When entering into the station, ultimately we will decelerate the train and reduce the accidents of metropolitabn railroad traffic by securing safe driving.

• International Journal of Railway
• /
• v.9 no.2
• /
• pp.36-40
• /
• 2016

TETRA communication system is very versatile system which can transmit voice + data and packet data optimized. Direct mode operation permits to connect between mobiles when mobile stain is out of coverage of networks. It can be more secure communication channel for railway signaling systems. Railway signaling systems use many of wayside signal equipment, which require many maintenance efforts and budget. Many railway authorities want to reduce and replace the wayside equipment. Radio based signaling systems are one of candidate for replacing the conventional signaling systems. The radio based signaling systems can replace track circuit and wayside signal. The radio systems permit to connect between control centers and trains. The radio systems have to ensure high quality of the connectivity more or equal to the existed track circuits. We studied the application of TETRA systems for railway radio systems for bridging between train control centers and trains. We provide an operation scenario for radio based train control system to ensure the safety require to the existed trains control system and satisfied the existed operational availability. We showed the data transmission speed, maximum bit error rate, and data coding for the radio-based signal system using TETRA systems.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2018.05a
• /
• pp.68-71
• /
• 2018

In this paper, we propose a synchronization protocol for underwater acoustic networks which aims to minimize the effects of long propagation delay and uncertain delay variations and employs packet train scheme with considering low data rate. The proposed protocol uses an one-way delay measurement method by transmitting consecutive packets and acquires synchronization only considering propagation delay variations by calculating packet arrival time differences. We perform simulations under various network conditions, such as node mobility, time interval for packet transmission, network range, and elapsed time after synchronizing. The simulation results shows the superiority of our protocol, compared with a previously proposed protocol.