• Journal of KIISE:Information Networking
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• v.35 no.1
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• pp.56-66
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• 2008

Contention-based forwarding in wireless ad-hoc networks reduces transmission failure rate by selecting one receiver with good channel among multiple receivers. However, contention-based forwarding may increase transmission latency due to the collision problem caused by the simultaneous transmission among multiple receivers. In this paper, we present an analytic model that reflects the delay and collision rate of contention-based forwarding in lossy wireless links. Through the analytic model, we calculate the expected delay and progress in one-hop transmission under given wireless link model and delay model. Based on the analytic results, we observe that delay model should be adapted to wireless link model for optimal performance in contention-based forwarding.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.11
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• pp.9-16
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• 2012

In this paper, we focus on end-to-end transfer delay improvement by using network coding and propose a scheme where a message is divided into several packets which are network coded generating additional redundancy with the results that the number of transmitted packets increases. In networks with high coefficient of variation of transfer time, increased number of packets could reduce the transfer time of the message to a destination. For the proposed scheme, we investigate the optimum number of divided packets and redundancy considering transfer delay reduction and additional transmission cost caused by using network coding under the restriction of maximum transmission packet size. From the results of the investigation, we see that the proposed scheme is effective in networks having high variability of transfer time and would be very useful and practical especially for the case that expedited deliveries of messages are needed.

• Journal of Internet Computing and Services
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• v.9 no.2
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• pp.43-50
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• 2008

In IEEE 802.11b wireless LAN, stations keep synchronization by receiving beacons being periodically sent by the AP (access point) when they run in low power mode. Beacon transmission is delayed if wireless channel is busy at a scheduled TBTT (target beacon transmission time), and stations must be awake until they receive the delayed beacon. In this paper, we propose a scheme that stations get their transmission delayed if they have little time for successful data transmission by the next TBTT. Beacon transmission without delay is guaranteed at every TBTT with this method so that the awake time of low power stations to receive beacon can be reduced. The proposed method is simulated and its characteristics ore described with the analysis of the results. The measured results in terms of beacon delay show some enhancement in energy consumption.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10c
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• pp.207-209
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• 2000

인터넷전화 서비스는 저렴한 가격과, 타 서비스와 통합 및 가치부가(Value Added)면에서 기존의 전화에 비해 많은 장점을 가지고 있으나, 상대적으로 낮은 음질로 인하여 사용자의 요구를 만족시키지 못하고 있다. 이것은 현재 인터넷은 best-effort형 패킷 전달 서비스만을 제공하고 있기 때문에 전송지연, 패킷손실, 지터등을 보장할 수 있는 방법이 없기 때문이다. 본 논문에서는 인터넷전화에서 패킷손실이나 전송지연으로 인한 음질 저하문제를 SOLA 알고리즘을 이용해 보완하였다. 제시된 알고리즘에서는 송신측에서 패킷을 전송하면 수신측에서는 수신 패킷에 SOLA 알고리즘을 적용하여 수신 패킷을 사람이 인지하지 못하는 수준에서 확장하여 전송지연으로 인한 패킷손실을 감소시킨다. 시뮬레이션 결과 전송지연으로 인한 패킷 손실 확률이 상당히 감소되었고 음질 또한 상당히 개선되었다.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.04a
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• pp.609-611
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• 2012

논문에서는 로우듀티사이클 환경을 고려하여 목적지까지 데이터 전송의 신뢰성뿐만 아니라 낮은 데이터 지연도 보장하는 DIGF (Delay Improvement Greedy Forwarding) 기법을 제안한다. 초기에 제안된 그리디 포워텅 기법들은 무선링크가 갖는 비신뢰성 및 비대칭성의 문제점을 해결하기 위해 데이터 전송 성공률과 에너지 효율을 높이는 기법이 제안되었다. 하지만 많은 그리디 포워텅 기법들은 노드들이 데이터를 송수신하기 위해 대기하고 있는 수신대기상태로 인한 많은 에너지 소모를 고려하지 않아 네트워크 라이프타임을 감소시킨다. 이러한 문제점을 해결하고자 제안기법인 DIGF는 무선링크의 비신뢰성과 비대칭성을 고려할 뿐만 아니라 로우듀티사이클 환경을 고려한다. 또한 로우듀티사이클 환경을 고려할 때 발생되는 높은 수면지연성 (Sleep latency) 을 해결하기 위한 알고리즘을 제안하여 낮은 전송지연과 신뢰성 있는 데이터 전송을 보장한다.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 1999.12a
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• pp.121-129
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• 1999

When continuous media are transmitted over the communication networks, asynchrony which can not maintain temporal relationships among packets may occur due to a random transit delay. There exist two types of synchronization schemes ; for guaranteed or non-guaranteed resource networks. The former which applies a resource reservation technique maintains delay characteristics, however, the latter supply a best-effort service. In this paper, I propose a intra-media synchronization scheme to transmit continuous media on general networks not guaranteeing a bounded delay tome. The scheme controls transmission times of the packets by estimating next delay time with the delay distribution. So, the arriving packets may be maintained within a limited delay boundary, and playout will be performed after buffering to smoothen small delay variations. The continually increasing delay due to network overload causes buffer underflow at the receiver. To solve it, the transmitter is required to speed up instantaneously. Too much increase of transmission-rate may cause network congestion. At that time, the transmitter drops the current packet when informed excessive delay from the receiver.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.6
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• pp.1317-1322
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• 2014

This paper shows effects of tropospheric delay models and mapping functions among delay features occurred when GPS code signal is transferred for GPS Time Transfer. GPS time transfer uses CGGTTS as the international standard format. For geodetic GPS receiver, ROB has provided r2cggtts software which generates CGGTTS data from RINEX data and all laboratories participated in TAI link use this software and send the CGGTTS results periodically. Though Saastamoinen zenith path model and Niell mapping function are commonly used in space geodesy, r2cggtts software applied NATO zenith path model and CHAO mapping function to the tropospheric delay model. Hence, this paper shows effects of two tropospheric delay models by implementing Saastamoinen model and Niell mapping function for the time offset.

• The KIPS Transactions:PartC
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• v.15C no.5
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• pp.367-374
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• 2008

To realize the voice privacy between CDMA mobile phone and PSTN terminal, the voice frames shall be transmitted transparently between the heterogeneous networks. For satisfying this requirement, we propose the method which transmits voice frames using the CDMA circuit data channel in real time. In this paper we analyze the causes of voice delay which occurs during voice transmission using circuit data channel. And in order to overcome this kind of delay, the technique controlling the TCP control flag and the variable audio block construction algorithm according to the vocoder output rate are proposed. As a result of experimenting by applying the proposed method, we confirmed that the transit delay was improved with about average 70%.

• Journal of Internet of Things and Convergence
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• v.6 no.3
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• pp.1-6
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• 2020

This paper aims to integrate the previous models about mean object transfer latency in one framework and analyze the result through the computational experience. The analytical object transfer latency model assumes the multiple packet losses and the Internet of Things(IoT) environment including multi-hop wireless network, where fast re-transmission is not possible due to small window. The model also considers the initial congestion window size and the multiple packet loss in one congestion window. Performance evaluation shows that the lower and upper bounds of the mean object transfer latency are almost the same when both transfer object size and packet loss rate are small. However, as packet loss rate increases, the size of the initial congestion window and the round-trip time affect the upper and lower bounds of the mean object transfer latency.

• Journal of the Institute of Convergence Signal Processing
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• v.22 no.2
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• pp.64-70
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• 2021

Nowadays, there are significant interests in real-time remote control using wireless networks. In implementing real-time remote control, one important factor is delay performance of real-time control message. Especially, the technique to reduce jitter of delay is necessary in transmitting periodically real-time control message. In this paper, we proposed synchronized transmission to reduce jitter of delay, when real-time control message was transmitted through wireless networks. The proposed transmission kept synchronization between source node and wireless transmitter and controlled transmission instance to transmit real-tie control message with fixed delay in wireless networks. According to results of experiment in military unmanned vehicle system, the proposed transmission reduced jitter of delay as 32% as that of a non-employing case.