• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권11호
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• pp.4585-4603
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• 2015

Video streaming services make up a large proportion of Internet traffic on both fixed and mobile access throughout the world. Adaptive streaming allows for dynamical adaptation of the bitrate with varying network conditions, to guarantee the best user experience. Adaptive bitrate algorithms face a significant challenge in correctly estimating the throughput as it varies widely over time. In this paper, we first evaluate the throughput estimation techniques and show that the method that we have used offers stable response to throughput fluctuations while maintaining a stable playback buffer. Then, we propose an adaptive bitrate scheme that intelligently selects the video bitrates based on the estimated throughput and buffer occupancy. We show that the proposed scheme improves viewing experience by achieving a high video rate without taking unnecessary risks and by minimizing the frequency of changes in the video quality. Furthermore, we show that it offers a stable response to short-term fluctuations and responds swiftly to large fluctuations. We evaluate our algorithm for both constant bitrate (CBR) and variable bitrate (VBR) video content by taking into account the segment sizes and show that it significantly improves the quality of video streaming.

• Journal of Communications and Networks
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• 제18권2호
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• pp.261-269
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• 2016

In this paper, the impact of energy constraints on a two-hop network with a source, a relay and a destination under random medium access is studied. A collision channel with erasures is considered, and the source and the relay nodes have energy harvesting capabilities and an unlimited battery to store the harvested energy. Additionally, the source and the relay node have external traffic arrivals and the relay forwards a fraction of the source node's traffic to the destination; the cooperation is performed at the network level. An inner and an outer bound of the stability region for a given transmission probability vector are obtained. Then, the closure of the inner and the outer bound is obtained separately and they turn out to be identical. This work is not only a step in connecting information theory and networking, by studying the maximum stable throughput region metric but also it taps the relatively unexplored and important domain of energy harvesting and assesses the effect of that on this important measure.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권11호
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• pp.5455-5475
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• 2016

In this article, we model the distributed relay assignment network as a many-to-one matching market with peer effects. We discuss two scenarios for throughput optimization of relay networks: the scenario of aggregate throughput optimization and the scenario of fairness performance optimization. For the first scenario, we propose a Mutual Benefit-based Deferred Acceptance (MBDA) algorithm to increase the aggregate network throughput. For the second scenario, instead of using the alternative matching scheme, a non-substitution matching algorithm (NSA) is designed to solve the fairness problem. The NSA improves the fairness performance. We prove that both two algorithms converge to a globally stable matching, and discuss the practical implementation. Simulation results show that the performance of MBDA algorithm outperforms existing schemes and is almost the same with the optimal solution in terms of aggregate throughput. Meanwhile, the proposed NSA improves fairness as the scale of the relay network expands.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2005년도 생물공학의 동향(XVII)
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• pp.422-423
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• 2005

• 정보과학회 컴퓨팅의 실제 논문지
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• 제21권12호
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• pp.780-785
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• 2015

최근 HTTP (Hypertext Transfer Protocol) 적응적 비디오 스트리밍 서비스가 주목 받고 있다. 기존 HTTP 적응적 비디오 스트리밍 서비스의 비디오 품질 조절 기법은 세그먼트 처리량을 표본으로 대역폭을 예측하고 평탄화 (Smoothing)를 한다. 그러나 기존 기법은 고정된 표본 개수로 평탄화를 하기 때문에 버퍼 언더플로우와 빈번한 품질 변화가 발생하여 QoE (Quality of Experience)를 저하시키는 문제가 있다. 본 논문에서는 이 문제를 해결하기 위해 세그먼트 처리량과 버퍼 점유율 기반의 비디오 품질 조절 기법을 제안한다. 제안 기법은 세그먼트 처리량 변화에 따라 표본의 개수를 적응적으로 결정하고 안정적인 버퍼 점유율을 유지할 수 있는 비트율의 임계값을 기반으로 비디오 품질 조절을 한다. 실험을 통해 제안 기법이 기존 기법에 비하여 버퍼 언더플로우 발생을 방지하고 품질 변화를 감소시켜 QoE를 향상시키는 것을 확인하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2004년도 ICEIC The International Conference on Electronics Informations and Communications
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• pp.143-146
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• 2004

Differentiated services (DiffServ) has been widely accepted as the service model to adopt for providing quality-of­service (QoS) over the next-generation IP networks. There is a growing need to support QoS in mobile ad hoc networks. Supporting DiffServ in mobile ad hoc networks, however, is very difficult because of the dynamic nature of mobile ad hoc networks, which causes network congestion. The network congestion induces long transfer packet delay and low throughput which make it very difficult to support QoS in mobile ad hoc networks. We propose DiffServ module to support differentiated service in mobile ad hoc networks through congestion control. Our DiffServ module uses the periodical rate control for real time traffic and also uses the best effort bandwidth concession when network congestion occurs. Network congestion is detected by measuring the packet transfer delay or bandwidth threshold of real time traffic. We evaluate our mechanism via a simulation study. Simulation results show our mechanism may offer a low and stable delay and a stable throughput for real time traffic in mobile ad hoc networks.

• Journal of Communications and Networks
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• 제14권2호
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• pp.162-168
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• 2012

This paper considers the scenario in which a set of nodes share a common channel. Some nodes have a rechargeable battery and the others are plugged to a reliable power supply and, thus, have no energy limitations. We consider two source-destination pairs and apply the concept of cognitive radio communication in sharing the common channel. Specifically, we give high-priority to the energy-constrained source-destination pair, i.e., primary pair, and low-priority to the pair which is free from such constraint, i.e., secondary pair. In contrast to the traditional notion of cognitive radio, in which the secondary transmitter is required to relinquish the channel as soon as the primary is detected, the secondary transmitter not only utilizes the idle slots of primary pair but also transmits along with the primary transmitter with probability p. This is possible because we consider the general multi-packet reception model. Given the requirement on the primary pair's throughput, the probability p is chosen to maximize the secondary pair's throughput. To this end, we obtain two-dimensional maximum stable throughput region which describes the theoretical limit on rates that we can push into the network while maintaining the queues in the network to be stable. The result is obtained for both cases in which the capacity of the battery at the primary node is infinite and also finite.

• 한국통신학회논문지
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• 제28권10A호
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• pp.780-787
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• 2003

적응변조방식은 이동통신 시스템의 설계 전력 여유분을 이용하여 기존 시스템의 구성을 가능한 변경하지 않고 시스템의 전반적인 전송효율을 증진시킬 수 있는 방식으로 대두되고 있다. 일반적으로 적응변조방식의 성능을 다루기 위한 논리에 중점을 두고, 귀환 경로에 대한 것을 제시하지 않고 가정하여 왔으나 본 논문에서는 양방향성의 성능을 모색하여 시스템의 성능을 개선하는 것 뿐만 아니라, 시스템의 안정성을 고려하기 위해 수시로 변조방식이 바뀌는 경우에는 시스템의 안정성이 떨어지고, 이에 따라 전체적인 시스템 성능이 약화되므로 귀환 경로를 이용하여 시스템의 안정성을 기하기 위해 단말기의 이동성을 측정하므로써 변경의 조건을 확실하게 한 후 변경하여, 시스템의 안정성을 향상하고 전체적인 성능을 향상 시키는 방식을 제시한다. 제안된 방식은 기지국에서 이동국의 거리를 전력제어를 통해 파악하며. 적응변조방식으로 MPSK를 적용하고. 이동국의 순시 변화치를 적용함으로써 이동성에 따른 변화를 감지하여 적용시점을 결정하는 변수를 적용하여. 전체적인 시스템의 안정성을 확보하면서 전송효율을 증진 시킬 수 있다.

• 한국항만경제학회지
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• 제35권4호
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• pp.169-186
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• 2019

이 연구는 2007-2015년 여수항과 광양항의 화물 처리량을 대상으로 하여 국내 항만과 비교함으로써 여수광양항의 발전 방향을 제시하고자 한다. 이를 위해 국내 항만의 화물 처리 실적의 집중 지수를 도출하고, 여수·광양항 부두와 선사별 컨테이너 화물처리 실적 및 상대 지역별 화물처리 실적의 집중 지수를 도출하였다. 주요 결과는 첫째, 총화물 처리 실적의 경우, 여수·광양항은 부산항에 비해 두 번째로 비중이 높았으며, 지난 9년 동안의 집중지수(HHI)는 비교적 낮은 편이었다. 둘째, 수출입 총화물 처리실적의 경우, 여수광양항이 줄곧 1위인 가운데, 이 기간 동안 최저 1,790에서 2,099 사이의 비교적 안정적인 HHI 지수를 보여 주고 있었다. 셋째, 국적 선사별 컨테이너 처리 실적의 집중 지수는 1,800 이하의 안정된 수준을 보였다. 넷째, 여수광양항의 상대 지역(국가)별 화물처리 특별히 눈에 띄게 물동량이 집중되어 있는 지역이 나타나지 않았으며, 여러 지역에 걸쳐 고르게 물동량 실적을 보여주었다. 한진해운 위기 사태 이후 국적 선사에 있어 변화가 예상되는 가운데, 여수광양항의 특정 선사에서의 의존 정도는 크게 우려할 수준은 아니었던 것으로 나타났다. 향후 시설사용의 현실화와 여수광양 지역의 입주 업종의 다양화, 체선율 개선 등을 통해 더욱 발전할 수 있을 것으로 예상된다.

• Journal of Communications and Networks
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• 제12권5호
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• pp.499-509
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• 2010

A plethora of transmission control protocol (TCP) congestion control algorithms have been devoted to achieving the ultimate goal of high link utilization and fair bandwidth sharing in high bandwidth-delay product (HBDP) networks. We present a new insight into the TCP congestion control problem; in particular an end-to-end delay-based approach for an HBDP network. Our main focus is to design an end-to-end mechanism that can achieve the goal without the assistance of any network feedback. Without a router's aid in notifying the network load factor of a bottleneck link, we utilize goodput and throughput values in order to estimate the load factor. The obtained load factor affects the congestion window adjustment. The new protocol, which is called TCP-goodput and throughput (GT), adopts the carefully designed inversely-proportional increase multiplicative decrease window control policy. Our protocol is stable and efficient regardless of the link capacity, the number of flows, and the round-trip delay. Simulation results show that TCP-GT achieves high utilization, good fairness, small standing queue size, and no packet loss in an HBDP environment.