• Journal of Broadcast Engineering
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• v.10 no.3
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• pp.401-412
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• 2005

We propose and design the algorithms of symbol timing recovery, carrier recovery, and equalization for the receiver of S-DMT cable modem, which supports more channels and better symmetric mutimedia services over HFC network. We evaluate the performance of the concatenated entire receiving system of 16QAM, 64QAM in the mixed noise channel of AWGN, ISI and impulse. The result of evaluation shows those algorithms work correctly and designed S-DMT receiver has good performance. We also verify the designed system has excellent immunity against impulse noise channel of practical Cable TV networks by the result of simulation with the parameters of impulse internal $\varepsilon$ and noise power $\gamma^{k}$.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.5
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• pp.714-724
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• 2022

The spread of mobile devices comes to increase explosive data traffic and then results in various types of service demands. In order to satisfy the increment of traffic and the requirements for various services, optical internet technologies that transmit several Tbps through only a single optical fiber have been actively studied. Because of the large bandwidth, an optical link can accommodate a large number of service types. Therefore, new technologies are required to guarantee the survivability of optical internet and handle the requirements of each service. So, in this article, a new scheme based on GMPLS technologies is proposed to deal with the various service demands and survivability issues in IP over WDM networks.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10c
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• pp.381-383
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• 2000

최근 인터넷의 트래픽이 다양해지고, 서비스 질 보장에 대한 사용자의 요구가 증가하며, 가상 사설망(VPN, Virtual Private Network)이나 트래픽 엔지니어링 등 향상된 IP 서비스가 요구되고 있다. 이러한 요구 사항을 충족시켜주기 위하여 IETF에서는 MPLS (Multiprotocol Label Switching) 기술을 표준화하고 있다. 다양한 서비스와 QoS 보장을 가능하게 하는 MPLS 망에서 신뢰성(Reliable) 보장은 또 하나의 중요한 문제이다. 본 논문에서는 이러한 MPLS 망의 신뢰성을 보장하기 위한 기존의 방법들을 설명하고 기존 방법의 문제를 해결하기 위해 선택적인 보호 연결(Protection Path) 설정방법을 제안한다. 본 논문에서 제안하는 보호 연결 설정방법은 과거의 특정 장애 정보를 이용하여 선택적으로 보호 연결을 미리 설정함으로써 빠른 연결 복구를 수행하게 하고 보호 연결 설정으로 인한 자원의 낭비를 최소화 하고자 하는 방법이다.

• Journal of Information Processing Systems
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• v.6 no.3
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• pp.413-434
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• 2010

Wireless sensor networks are usually characterized by dense deployment of energy constrained nodes. Due to the usage of a large number of sensor nodes in uncontrolled hostile or harsh environments, node failure is a common event in these systems. Another common reason for node failure is the exhaustion of their energy resources and node inactivation. Such failures can have adverse effects on the quality of the real-time services in Wireless Sensor Networks (WSNs). To avoid such degradations, it is necessary that the failures be recovered in a proper manner to sustain network operation. In this paper we present a dynamic Energy efficient Real-Time Job Allocation (ERTJA) algorithm for handling node failures in a cluster of sensor nodes with the consideration of communication energy and time overheads besides the nodes' characteristics. ERTJA relies on the computation power of cluster members for handling a node failure. It also tries to minimize the energy consumption of the cluster by minimum activation of the sleeping nodes. The resulting system can then guarantee the Quality of Service (QoS) of the cluster application. Further, when the number of sleeping nodes is limited, the proposed algorithm uses the idle times of the active nodes to engage a graceful QoS degradation in the cluster. Simulation results show significant performance improvements of ERTJA in terms of the energy conservation and the probability of meeting deadlines compared with the other studied algorithms.

• The Transactions of the Korea Information Processing Society
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• v.5 no.12
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• pp.3185-3193
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• 1998

ATM망은 망 내부의 큐잉 랜덤 지연에 의한 CDV의 발생으로 클럭복원의 문제를 안고 있다. 큐잉에 의한 지연은 여러 가지 파라메터에 의해 좌우되며 특히 망의 부하와 트래픽이 전송되는 교환기의 수에 의해 크게 좌우된다. CBR 트래픽의 경우 이를 해결하기 위해 SAR 헤더에 송신부의 클럭 정보를 담아 보내고 수신부에서는 이 정보를 바탕으로 송신부의 클럭을 복원하는 SRTS 기법을 사용하고 있다. 그러나 실시간성을 요하는 VBR 트래픽은 CBR과는 달리 대역폭의 가변적인 성질을 가지고 있으며 그 변화가 다양하여 SRTS 기법을 그대로 적용하기 곤란하다. VBR의 경우에 CBR 전송을 위한 SRTS 기법을 그대로 적용하면 주파수의 가변성으로 인해 망 클럭 주파수에 비해 매우 낮은 주파수의 경우에는 사이클이 상대적으로 많아 정보의 정확성이 떨어지게 된다. 이를 방지하기 위해 서비스 클럭의 주파수가 낮은 경우에는 망 기준 주파수를 낮게 하므로써 정확성을 증가시킬 수 있다. 또한, VBR 트래픽의 경우 AAL1에서는 SRTS의 필요성이 강조되지 않으나 단지 CDV를 제거할 방법이 요구되어진다. 따라서 AAL1의 SRTS를 CDV의 측정을 위한 메카니즘으로 바꾸는 것이 필요하며, 각 기반으로하여 Wavelet 변환을 이용한 VBR 트래픽의 클럭 복원방식을 제안한다. 제안된 알고리즘은 ATM망에서 VBR 영상 서비스를 위한 AAL 계층에 이용이 가능하다. 시뮬레이션 결과는 wavelet 변환 블록에서 출력되는 계수 값을 선택하여 전송함으로써 VBR 트래픽의 보다 다양한 QoS를 만족시킬 수 있음을 보인다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.3
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• pp.341-357
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• 2010

Forward Error Correction (FEC) techniques have been adopted to overcome packet losses and to improve the quality of video delivery. The efficiency of the FEC has been significantly compromised, however, due to the characteristics of the wireless channel such as burst packet loss, channel fluctuation and lack of Quality of Service (QoS) support. We propose herein an Adaptive Cross-layer FEC mechanism (ACFEC) to enhance the quality of video streaming over 802.11 WLANs. Under the conventional approaches, FEC functions are implemented on the application layer, and required feedback information to calculate redundancy rates. Our proposed ACFEC mechanism, however, leverages the functionalities of different network layers. The Automatic Repeat reQuest (ARQ) function on the Media Access Control (MAC) layer can detect packet losses. Through cooperation with the User Datagram Protocol (UDP), the redundancy rates are adaptively controlled based on the packet loss information. The experiment results demonstrate that the ACFEC mechanism is able to adaptively adjust and control the redundancy rates and, thereby, to overcome both of temporary and persistent channel fluctuations. Consequently, the proposed mechanism, under various network conditions, performs better in recovery than the conventional methods, while generating a much less volume of redundant traffic.

• 재활복지
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• v.21 no.2
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• pp.247-259
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• 2017

We investigated the improvement of cognitive functions, activity of daily living (ADL), and quality of life (QoL) after hemorrhagic stroke and identified associated factors. For this research, twenty-five patients with a hemorrhagic stroke were enrolled. We measured cognitive function, activity of daily living (ADL), and quality of life (QoL) from 7 days to 12 months after onset of stroke. Then we analyzed the correlation between cognitive function and other risk factors. According to results, cognitive functions improved during 12 months with statistically significant differences. Other functions were similar to cognitive functions. Improvement of cognitive functions were correlated with age, the type of hemorrhagic stroke and Glasgow coma scale at 7 days after stroke. Overall, cognitive function in patients with hemorrhagic stroke recovered from acute to 12 months after onset of stroke. And, improvement of cognitive function at this phase were associated with age, the type of hemorrhagic stroke and GCS score at 7 days. These results would provide us an information to plan cognitive rehabilitation in patients with hemorrhagic stroke.

• The KIPS Transactions:PartC
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• v.10C no.3
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• pp.345-354
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• 2003

IP Multicast is required of more little network resources than one in unicast. Furthermore, reliable multicast has been researched for supporting reliability at IP Multicast mechanism. Although these studies are carried out, they only have focused on general data. In other words, in case that realtime packet, they can not support reliability since they do not consider realtime properties such as dependency of interframe and playback in time. Besides, we also request to support scalability because we are based on Mobile IP network together with internet. Thus, we need a mechanism to guarantee reliability and scalability of realtime stream data. In this paper, we propose PER (Preceding Error Recovery) that reflect characteristics of the realtime data, especially for H.323. PER provides scalable reliability because it is based on tree-based multicast basically and helps to support scalable relibility as reducing control packet and recovers stream buffer space from underflow status as soon as possible. PER shows much better scalable and reliable than existing works.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.8A
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• pp.639-648
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• 2005

A wireless ad-hoc network is a temporal network formed by a collection of wireless mobile nodes without the aid of any existing network infrastructure or centralized ad-ministration. Numerous routing protocols have been developed for changing messages among the nodes in a wireless ad-hoc network. Some multi-path routing protocols have also been proposed to support load balancing and QoS for wireless ad-hoc networks. In this paper, we propose not only an efficient routing algorithm for wireless ad-hoc net-worts but also a protocol that can improve data transmission rate and reduce end-to-end delay. In our protocol, each mobile node need not broadcast routing messages periodically and the mobile node that wants to send data packets initiates route request and route establishment procedure. By simulation, we showed that faster route recovery is possible by maintaining multiple routing paths in each node, and the route maintenance overhead can be reduced by limiting the number of multiple routing paths.

• Journal of Digital Convergence
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• v.20 no.3
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• pp.377-388
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• 2022

Various researches are actively studied to satisfy exponentially increasing the usage of the Internet as well as the diverse service demands. Especially the Optical Internet that delivers several Tbps through a single optical fiber requires the intelligence to satisfy the various types of survivability requirements. In the paper, a novel recovery scheme that satisfies the various restoration demands in IP over WDM networks is proposed. The scheme classifies the restoration services into three classes and applies dedicated protection and shared restoration scheme with different priorities for each class. Also, a configuration scheme for information database to support the scheme is proposed. This scheme satisfies the different degree of restoration demands in terms of restoration time, blocking rate and resource usage. With the scheme, medical data can be transmitted without loss.