• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.12
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• pp.2265-2270
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• 2007

This paper discusses a tester of functionality and call processing performance, based on the MEGACO/H.248 protocol that both IETF and ITU-T recommend as a media gateway control protocol, of both a media gateway controller and an access gateway which constitute a next generation convergence network. Effective methods, a functional architecture and implementation for such testification are provided. Especially included are not only a virtual emulation function of analog subscriber lines connecting to an access gateway, but also a tester emulated as a counter system of the protocol for the testifying a media gateway controller and an access gateway system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.6
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• pp.1333-1340
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• 2015

IEEE 802.11 MAC(Media Access Control) defines DCF(Distributed Coordination Function) for data transmission control. BEB(Binary Exponential Backoff) algorithm of DCF has a problem that if the number of stations connected are over a certain threshold, it degrades network performance because of packet collisions caused from the minimum contention window size. To cope with this problem, we proposed a novel algorithm, named as VBS(Variable Backoff Stage) algorithm, which adjusts the rate of backoff stage increment depending on the number of stations associated with an AP(Access Point). Analytic model of proposed algorithm was derived and simulations on the BEB and the VBS algorithms have been conducted on the OFDM (Orthogonal Frequency Division Multiplexing) method. Simulation results showed that when the rate of backoff state increment was 5 and 10, the number of retransmission were reduced to 1/5 and 1/10 comparing to that of BEB, respectively. Our algorithm showed improvement of 19% and 18% in network utilization, respectively. Packet delay was reduced into 1/12.

• The Journal of the Acoustical Society of Korea
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• v.20 no.7
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• pp.101-108
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• 2001

In this paper we focus on dynamic reservation slot allocation scheme for supporting QoS of a voice traffic in WATM MAC. Especially, voice traffic is the most important real-time object, and so we propose a new MAC protocol for voice traffic over WATM networks in the multimedia environment. According to the characteristics of voice traffic which is repeatedly in silent state and active state, new protocol allocates reservation slots dynamically with respect to the number of silent voice source of which starting time is stored to the state table in base station (BS). The simulation results show that the proposed protocol has better performance than slotted ALOHA in average access delay, collision rate, better than NC-PRMA(Non Collision Packet Reservation Multiple Access) in band width efficiency, and can provide a certain level of QoS requirement by the given slot assignment even though the number of voice terminals is increased.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.3
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• pp.534-541
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• 2018

The number of stations existing in the same wireless channel is increasing due to the spread of the wireless LAN devices. CSMA/CA, a conventional wireless LAN protocol, uses a random backoff method. In the random backoff scheme, collision between stations is frequent in a dense region where the number of stations existing in the same channel is several tens or more, and the performance of the performance degradation of such a protocol, the IEEE 802.11ah standard proposed a Restricted Access Window(RAW) wireless access method. RAW improves performance by limiting the number of concurrent access stations by dividing the stations into several groups. In this paper, we propose a method to improve the performance of channel connection by using new group creation, group removal and group relocation algorithm according to traffic change by improving existing RAW method.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.3
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• pp.292-301
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• 2014

This paper describes development of distributed type independent electro-hydraulic ballast valve remote control system with diagnostic function based on fuzzy inference using redundant Modbus communication and ethernet Modbus TCP/IP. Diagnostic function estimate degradation of system components and diagnose system faults, which results in shortage of fault maintenance time and improvement of system safety. Slave devices which control each valve and master device which command, monitor and diagnose slave system are developed. Slave devices are connected to master device with redundant Modbus networks and master device is connected to ship's integrated control system with Modbus TCP/IP. Also this paper describes development of simulator to test and confirm whether developed system can be integrated with ship's integrated control and monitoring system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9A
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• pp.1031-1038
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• 2004

The call admission control algorithm of hybrid scheme is proposed to enhance the QoS(quality of service) of attempted multimedia calls. In the initial stage of 3rd generation multimedia services networks, the major limitations include the small sefyice coverage and the limited radio link capacity. Because the initial massive deployment of network elements such as base stations, base station controllers, and mobile switching centers is restricted to populated areas and the other areas should be covered with the fewer network elements, the radio channel resources are hmited and coverage network is supposed to be established. Therefore the QoS of multimedia services is expected to be severely degraded when tentative traffic hot spot occurs frequently. Thus, the blocking probability of attempted calls mcreases when relatively large number of users try to place multimedia calls in a hot spot area of the wireless networks. In this situation, the proposed hybrid scheme can mitigate the degradation of the QoS of multimedia services by using the available radio channels of the neighboring cells.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.179-186
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• 2007

KTX control systems mutually control OBCS, ATC, MBU, TECA, MDT, ABU, HVAC, TRAE, PID and FDTR, KTX OBCS as master, and controls other sub-control devices as slave, using various serial lines. In order to analyze physical structure of various serial link lines and mutual data transmission structure, serial line analyzer is used in many ways. To use serial line analyzer, prior and professional technics about High Speed Train and experience of using device are necessary. In spite of difficult situation of space and environment where we work for maintenance of High Speed Train, in presenting basic structure about physical connection method aquired by sub-device serial line data collection and about communication data analysis, I hope that this research will be helpful for the person who work for similar area. Also, I hope that this research will help diagnostic work of High Speed Train, which is necessary for test run of independently developed High Speed Train.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.256-258
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• 2002

이동 컴퓨팅 환경에서는 무선 단말기 사용자의 이동에 따른 접속 단절 현상이 발생할 수 있다. 이러한 이동 컴퓨팅 환경에서 끊김없는 핸드오프와 효율적인 호 수락 제어를 지원하기 위해서 사용자의 이동성 예측이 중요하다. 따라서, 본 논문에서는 사용자의 이동성을 규칙적인 패턴과 임의적인 패턴으로 분류하고, 규칙적인 이동패턴을 예측하기 위하여 사용자의 과거 이동 경로를 분석하며 임의적인 이동패턴은 GPS의 정보를 이용하여 이동성을 예측한다. 이러한 예측 기법은 무선 단말기 사용자의 속도가 매우 빠르거나, 셀룰러망의 셀의 크기가 작은 경우에 보다 효율적으로 이동성을 예측할 수 있다는 장점이 있다.

• IE interfaces
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• v.25 no.4
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• pp.450-457
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• 2012

This study addresses the call admission control(CAC) problem for OFDMA wireless communication systems in which both subcarriers and power should be considered together as the system resources. To lessen the exccessive allocation of radio resources for protecting handoff calls, the proposed CAC allows the less data rate than their requirements to handoff calls. The CAC problem is formulated as a semi-Markov decision process(SMDP) with constraints on the blocking probabilities of handoff calls. Some extensive experiments are conducted to show the usefulness of the proposed CAC model.

• Journal of Korean Institute of Industrial Engineers
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• v.34 no.4
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• pp.445-459
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• 2008

This paper addresses a call admission control(CAC) scheme giving handoff calls a priority over new calls for OFDMA wireless communication systems. The characteristics of OFDMA system and a variety of user QoS (Quality of Service) requirements are incorporated into the proposed CAC scheme which consists of several optimization modules for the system resource(subcarriers and power) allocations. The mathematical models and its solution methods for the embedded resource allocation problems are proposed. Some extensive computational experiments are conducted to illustrate the superiority of our CAC.