• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권4호
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• pp.1006-1025
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• 2012

Improving the quality of service in IP networks is a major challenge for real-time voice communications. In particular, packet arrival-delay variation, so-called "jitter," is one of the main factors that degrade the quality of voice in mobile devices with the voice-over Internet protocol (VoIP). To resolve this issue, a receiver-based enhanced timing recovery algorithm combined with active jitter estimation is proposed. The proposed algorithm copes with the effect of transmission jitter by expanding or compressing each packet according to the predicted network delay and variations. Additionally, the active network jitter estimation incorporates rapid detection of delay spikes and reacts to changes in network conditions. Extensive simulations have shown that the proposed algorithm delivers high voice quality by pursuing an optimal trade-off between average buffering delay and packet loss rate.

• 유공압시스템학회:학술대회논문집
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• 유공압시스템학회 2010년도 춘계학술대회
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• pp.116-125
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• 2010

In this study, a novel hydraulic energy-regenerative system was presented from its proposal through its modeling to its control. The system was based on a closed-loop hydrostatic transmission and used a hydraulic accumulator as the energy storage system in a novel configuration to recover the kinetic energy without any reversion of the fluid flow. The displacement variation in the secondary unit was reduced, which widened the uses of several types of hydraulic pump/motors for the secondary unit. The proposed system was modeled based on its physical attributes. Simulation and experiments were performed to evaluate the validity of the employed mathematical model and the energy recovery potential of the system. The experimental results indicated that the round trip recovery efficiency varied from 22% to 59% for the test bench.

• 정보보호학회논문지
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• 제13권1호
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• pp.39-46
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• 2003

본 논문에서는 Greenberger-Home-Zeilinger(GHZ) 상태를 사용하는 메시지 복구형 양자 서명 기법을 제시한다. 이 기법은 기존의 양자 서명과 마찬가지로 중재자가 서명을 확인해주는 형식을 띄고 있으나, 기존에 제시된 양자 서명 기법에 비하여 메시지를 암호화시켜 외부에서 메시지에 대한 기밀성을 동시에 제공한다. 이와 더불어 전송상 효율을 높였으며, Bell측정을 사용하지 않고 단순 측정만을 사용함으로써 사용자의 편의를 증가시켰다.

• ETRI Journal
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• 제40권2호
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• pp.237-245
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• 2018

The Distributed Modulated Wideband Converter (DMWC) is a networking system developed from the Modulated Wideband Converter, which converts all sampling channels into sensing nodes with number variables to implement signal undersampling. When the number of sparse subbands changes, the number of nodes can be adjusted flexibly to improve the reconstruction rate. Owing to the different attenuations of distributed nodes in different locations, it is worthwhile to find out how to select the optimal sensing node as the sampling channel. This paper proposes the spectrum sensing of DMWC based on a Markov random field (MRF) to select the ideal node, which is compared to the image edge segmentation. The attenuation of the candidate nodes is estimated based on the attenuation of the neighboring nodes that have participated in the DMWC system. Theoretical analysis and numerical simulations show that neighboring attenuation plays an important role in determining the node selection, and selecting the node using MRF can avoid serious transmission attenuation. Furthermore, DMWC can greatly improve recovery performance by using a Markov random field compared with random selection.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(4)
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• pp.179-182
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• 2001

This paper has been studied a wavelet based still image transmission over the wireless channel. EZW(Embedded Zerotree Wavelet) is an efficient and scalable wavelet based image coding technique, which provides progressive transfer of signal resulted in multi-resolution representation. It reduces therefore the reduce cost of storage media. Although EZW has many advantages, it is very sensitive on error. Because coding are performed in subband by subband, and it uses arithmetic coding which is a kind of variable length coding. Therefore only 1∼2bit error may degrade quality of the entire image. So study of error localization and recovery are required. This paper investigates the use of reversible variable length codes(RVLC) and data partitioning. RVLC are known to have a superior error recovery property due to their two-way decoding capability and data partitioning is essential to applying RVLC. In this work, we show that appropriate data partitioning length for each SNR(Signal-to-Noise Power Ratio) and error localization in wireless channel.

• Journal of Power Electronics
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• 제15권5호
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• pp.1367-1379
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• 2015

A hybrid HVDC system that is composed of line commutated converter (LCC) at the rectifier side and voltage source converter (VSC) in series with LCC at the inverter side is studied in this paper. The start-up strategy, DC fault ride-through capability, and fault recovery strategy for the hybrid HVDC system are proposed. The steady state and dynamic performances under start-up, AC fault, and DC fault scenarios are analyzed based on a bipolar hybrid HVDC system. Furthermore, the immunity of the LCC inverter in hybrid HVDC to commutation failure is investigated. The simulation results in PSCAD/EMTDC show that the hybrid HVDC system exhibits favorable steady state and dynamic performances, in particular, low susceptibility to commutation failure, excellent DC fault ride-through, and fast fault recovery capability. Results also indicate that the hybrid HVDC system can be a good alternative for large-capacity power transmission over a long distance byoverhead line.

• 한국생산제조학회지
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• 제20권4호
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• pp.440-445
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• 2011

This paper presents a new regenerative brake system of electric vehicles that employs a continuous variable transmission(CVT) and a flywheel. The developed device has advantages over existing regenerative brakes from a standpoint of reliability and versatility in actual driving conditions. The system consists of a CVT, two wheels, a flywheel, a coupling and auxiliary powertrain components. The CVT is designed as a combination of two cones and a roller, which causes the velocity difference between the wheel and the flywheel. The power flow of the flywheel system is controlled by the CVT roller and the coupling through step motors. A prototype has been developed and then its performance has been investigated for various operating conditions. Results show that the storage efficiency of the flywheel is much affected by the vehicle's velocity and it is reduced below 20% for high speed, as compared to the 25% efficiency for an ideal condition. The CVT is a primary factor for lowering the flywheel efficiencies due to large friction and slipping between the cone and the roller.

• 한국콘텐츠학회논문지
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• 제6권2호
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• pp.65-74
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• 2006

MPEG-2 비디오 압축열은 복잡한 부호화 알고리즘을 이용하여 압축하기 때문에 전송 오류에 매우 민감하다. 만약 패킷을 잃어버리거나 수신된 패킷에 오류가 있으면 현재 화면에 화질저하가 발생할 뿐만 아니라 화면수가 제한적이긴 하지만 뒤이어서 재생되는 화면에도 오류가 전파된다. 따라서 이런 전송오류의 영향을 막거나 최소화 하기위해서 다양한 오류 강인 부호화/복호화를 적용한다. 대표적인 오류 강인 방법이 오류 은폐 기법이다. 오류 은폐 기법은 손상된 비디오 데이터를 은폐하기 위해서 정상적으로 수신된 데이터의 공간적, 시간적 중복성을 이용한다. 손상된 데이터를 복원하기 위해 움직임 벡터를 추정하고 움직임 보상하는 것은 좋은 방법이다. 이 논문에서는 다양한 움직임 벡터 복원 방법에 기반한 오류 은폐 기법을 제안하고 일반적인 방법들과 성능을 비교한다.

• 대한전자공학회논문지SD
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• 제48권6호
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• pp.33-38
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• 2011

최근들어 모바일기기의 다기능화 와 고성능화로 인하여, 배터리 사용량이 증가하고 있다. 하지만 필요한 컴퓨팅 파워에 비하여 배터리의 에너지 용량증가의 연구는 더디게 진행되고 있다. 그러므로 본 논문에서는 우리는 배터리 방전특성을 이용하여, 배터리의 사용가능 유효용량을 증가시키는 연구를 하였으며, 무선 전송에서 시스템파워를 끄는 것만으로 배터리 사용시간 연장을 하는 기술을 설명한다. 실험은 표준영상 전송을 통하여 배터리 방전간격에 따른 배터리 사용시간을 측정하고, 사용될 어플리케이션과 발견적 실험을 통하여 배터리 사용시간의 최적화를 달성하였다.

• Journal of information and communication convergence engineering
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• 제10권3호
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• pp.231-236
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• 2012

For real-time wireless sensor network applications, it is essential to provide different levels of quality of service (QoS) such as reliability, low latency, and fault-tolerant traffic control. To meet these requirements, an (m,k)-firm based real-time routing protocol has been proposed in our prior work, including a novel local transmission status indicator called local DBP (L_DBP). In this paper, a fault recovery scheme for (m,k)-firm real-time streams is proposed to improve the performance of our prior work, by contributing a delay-aware forwarding candidates selection algorithm for providing restricted redundancy of packets on multipath with bounded delay in case of transmission failure. Each node can utilize the evaluated stream DBP (G_DBP) and L_DBP values as well as the deadline information of packets to dynamically define the forwarding candidate set. Simulation results show that for real-time service, it is possible to achieve both reliability and timeliness in the fault recovery process, which consequently avoids dynamic failure and guarantees meeting the end-to-end QoS requirement.