• The KIPS Transactions:PartC
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• v.14C no.7
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• pp.571-582
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• 2007

Vehicular ad-hoc networks is temporarily established through inter-vehicle communication without any additional infrastructure aids. It requires a immediate message propagation because it mainly deals with critical traffic information such as traffic accidents. The distance-based broadcast scheme is one of the representative broadcast schemes for vehicular ad-hoc network. In this scheme, a node to disseminate messages is selected based on a distance from a source node. However, a message propagation delay will be increased if the relay nodes are not placed at the border of transmission range of the source node. In particular, when the node density is low, the message propagation delay is getting longer. In this paper, we propose a time-window reservation based relay node selection scheme. A node receiving the alert message from the source node has its time-window and randomly selects its waiting time within the given time-window range. A proportional time period of the given time-window is reserved in order to reduce the message propagation delay. The experimental results show that the proposed scheme has shorter message propagation delay than the distance-based broadcast scheme irrespective of node density in VANET. In particular, when the node density is low, the proposed scheme shows about 26% shorter delay and about 46% better performance in terms of compound metric, which is a function of propagation latency and network traffic.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.1
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• pp.50-60
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• 2015

A Block-Time-Bounded Time Division Multiple Access (BTB-TDMA) medium access control protocol, which estimates the propagation delay of nodes according to their location and moving velocity information, has been proposed for underwater acoustic networks. BTB-TDMA provides nodes with their transmission schedules by a time block that is a time unit, newly designed for BTB-TDMA. In this paper, we investigate how the receiver collision, that is induced by the asymmetry between node's uplink and downlink propagation delay due to its mobility, affects the performance of BTB-TDMA. To do this, we analytically obtain the collision rate, the channel access delay, and the channel utilization by considering the asymmetry of propagation delay. Then, simulations are extensively performed with respect to the length of a time block by varying the number of nodes, the network range, and the node's velocity. Thus, the simulation results can suggest performance criteria to determine the optimal length of a time block which minimizes the collision rate and concurrently maximizes the channel access delay and the channel utilization.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.14 no.4
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• pp.293-306
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• 1989

In this paper, the models and characteristics of multipath propagation in an urban environment are described. Three propagation models(a random model, a ray model and a method of estimating time delay is proposed based on the envelope correlation between two radio frequencies. It is shown on the basis of laboratory simulation and field tests that the simple two-ray model is an adequate model for the fundamental study of the multipath propagation characteristic of the mobile radiowave and the estimating time delays of multipath-propagated waves in an urban area.

• Journal of Astronomy and Space Sciences
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• v.9 no.1
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• pp.69-88
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• 1992

The effects of the ionosphere on the radio wave propagation are scattering of radio waves, attenuation, angle error, ranging error, and time delay. If ionospheric conditions are suitable, the charged particles can remove energy from radio waves and thus attenuate the signal. Also, a radio wave traveling a path along which the electron density is not constant undergoes changes in direction, positon and time of propagation. The present study is based on Korean ionospheric data obtained at the AnYang Radio Research Institute from Jan. 1985 through Oct. 1989. The data are used to simulate the Korean ionosphere following the Chapman law. The effects of the model ionosphere on the radio wave propagation, such as the angle, position error, time delay, and the attenuation, are studied for the various cases of the wave frequency and the altitude.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.04a
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• pp.611-614
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• 2011

본 논문에서 우리는 이종사업자망이 연동된 통합망 환경에서 네트워크 성능 저하 구간을 탐색하기 위해 RTCP(Real-time Transport Control Protocol)의 타임스탬프 정보를 이용한 네트워크 구간별 지연 시간을 측정할 수 있는 트래픽 모니터링 방안을 제안한다. 실시간 멀티미디어 서비스(IPTV, VoIP)의 이용이 증가함에 따라 이종망간 연동 환경에서 실시간 서비스에 대한 QoS 관리 방안이 반드시 필요하다. 영상회의, VoIP(Voice over IP) 및 IPTV 서비스와 같은 멀티미디어 서비스는 네트워크 성능(지연, 지연변이 및 패킷 손실)에 매우 민감하기 때문에 연동망 환경에서 서비스 품질이 저하될 경우 어느 네트워크 구간에서 성능 저하가 발생하였는지 탐색하는 것은 매우 중요한 문제이다. 이에 우리는 RTCP 패킷을 이용한 구간별 지연시간 측정 방안을 제안하며 이 방안을 통해 네트워크 성능 저하가 발생한 구간을 탐색하고 정의할 수 있다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.3
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• pp.208-216
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• 2017

This paper presents the design method of an FMCW(frequency-modulated continuous-wave) altitude simulator which generates propagation delay signals according to target distances to test the radar altimeter. To improve the conventional RF method for creating delay signals, the simulator is designed by the RF-optics-RF method using optical delay lines. In addition, it is designed to simulate the Doppler shift and jamming that may occur in actual flight environment. In order to evaluate the performance of the developed simulator, the integration tests have been conducted with the radar altimeter. Through the test, we successfully verified the performance of the simulator.

• The KIPS Transactions:PartA
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• v.15A no.5
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• pp.243-248
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• 2008

This paper proposes a low-power carry look-ahead adder using multi-threshold voltage CMOS. The designed adder is compared with conventional CMOS adder. The propagation delay time is reduced by using low-threshold voltage transistor in the critical path. Also, the power consumption is reduced by using high-threshold voltage transistor in the shortest path. The other logic block is implemented with normal-threshold transistor. Comparing with the conventional CMOS circuit, the proposed circuit is achieved to reduce the power consumption by 14.71% and the power-delay-product by 16.11%. This circuit is designed with Samsung $0.35{\mu}m$ CMOS process. The validity and effectiveness are verified through the HSPICE simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.11A
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• pp.1613-1619
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• 2000

이 논문에서는 전파재널 측정 시스템을 이용하여 건물내 무선 채널의 전파특성인 실효 시간지연 확산과 경로손실을 측정하고 분석한 결과를 제시한다. 구성된 측정 시스템은 미끄럼 상관기를 이용한 대역확산 채널 측정 시스템에서 2 GHz에서 동작하며 3 m 의 분해능을 갖는다. 건물내 무선 채널 특성의 측정환경은 송신 안테나와 수신 안테나가 같은 층에 있을때, 서로 다른 층에 있을때, 그리고 사무실 안에 같이 위치할 때의환경으로구분하여 실험한다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2010.10a
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• pp.4-6
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• 2010

지상파 항법인 로란은 전송된 신호는 장파특성에 따라 지표파에 의한 정보를 전달하게 되는데 지표면과 해수면의 특성 즉, 전도도에 따라 전파의 지연시간이 달라진다. 이것은 정확도를 저하시키는 원인이 된다. 그러므로 보다 정확도가 요구되는 지역에서는 전파지연에 의해 발생하는 시간적 공간전 변화(ASF)를 보상하게 되면 정확도를 향상시킬 수 있다. 로란시스템의 현대화와 eLoran 시스템에서는 ASF를 보상함으로써 선박이 항만으로 진입 및 접안할 때 활용할 수 있는 정확도 기준을 마련하고 있다. 이 조건을 충족시키기 위해서는 ASF의 정밀측정 필수이며, 본 논문에서는 포항송신국 근해인 영일만 해상에서 ASF를 실측한 결과와 그에 필요한 측정기술을 보고한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.05a
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• pp.621-624
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• 2017

In this paper, we propose a protocol synchronizing to packet trains in a underwater acoustic networks with limitations such as long propagation delay, low data rate, high packet loss. The proposed protocol employs an one-way communication scheme to calculate packet arrival time differences of consecutively transferred packets and minimizes uncertain variation effect of long propagation delay. Simulation results shows the superiority of our protocol, compared with a previously proposed one under the given network conditions.