• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1567-1576
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• 2015

This paper proposes a reliable real-time data dissemination protocol for mitigating transmission failure of real-time data in WSNs. The re-transmission is well-known for recovery of transmission failure, but this may violate the real-time requirement by transmission delay. To solve this problem, the proposed protocol exploits broadcasting nature and temporal opportunity allocation. In a radio-range of sending node, there may be neighbors satisfying the real-time requirement. The neighbors of specific node could receive data simultaneously by broadcasting, and decide their priority using temporal opportunity allocation method. The method uses time slot and tolerable time. The time slot specifies the priority and transmission deadline for each neighbors, and the tolerable time is the real-time requirement at the sending node. By giving the priority to the node with shorter tolerable time in each slot, we may get more opportunities to forward toward the destination. In other words, even if a node have the longer tolerable time, it still has a chance to forward with the real-time requirement. Simulation results show that the proposed protocol is superior to the existing protocols.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.2787-2794
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• 2011

A mesh node, a component of a mesh network, is connected with the network by dynamic routing using routing protocol and collects the information of adjacent or connected mesh nodes for its self-management and settings. Also, it relays packets between the mesh nodes and provides AP(Access Point) with its corresponding functions based on IEEE 802.11 a/b/g for clients' access to the network. In this paper, the study focused on the design and performance tests of Wireless Mesh Network(WMN) which is applied to the wireless communication network for the CBTC(Communications Based Train Control) system. The WMN was established on a K-AGT test-line (Kyeongsan city, Gyeongsangbuk-do), and to verify the applicability, its operation and performances are checked by measuring the data throughput, delay latency, quality measurements such as transmission loss, radio interference and path recovery and setup between the on-board and wayside.

• ETRI Journal
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• v.35 no.3
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• pp.386-396
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• 2013

A 10-Gbit/s wireless communication system operating at a carrier frequency of 300 GHz is presented. The modulation scheme is amplitude shift keying in incoherent mode with a high intermediate frequency (IF) of 30 GHz and a bandwidth of 20 GHz for transmitting a 10-Gbit/s baseband (BB) data signal. A single sideband transmission is implemented using a waveguide-tapered 270-GHz high-pass filter with a lower sideband rejection of around 60 dB. This paper presents an all-electronic design of a terahertz communication system, including the major modules of the BB and IF band as well as the RF modules. The wireless link shows that, aided by a clock and data recovery circuit, it can receive $2^7$-1 pseudorandom binary sequence data without error at up to 10 Gbit/s for over 1.2 m using collimating lenses, where the transmitted power is 10 ${\mu}W$.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.281-284
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• 2002

Error resilience for image coding is an important component of multimedia communication system. Error resilience schemes address loss recovery from the compression perspective. Multiple description coding (MDC) is one of the error resilience techniques promising for robust video transmission. It is the way to achieve tradeoff description such as scalar quantization, correlating transform and the quantized frame expansion. In this paper, we consider Multiple Description Scalar Quantization (MDSQ) to wavelet domain. Conventional MDSQ schemes considered description with equal weights in each sub-bands. But, we can see that the each sub-bands is unequal contribution to whole image quality. Therefore, we experiment the multiple design MDSQ table to make probability of zero index high, which gives high efficiency in arithmetic symbol coder. We also compare our proposed method with the conventional methods and show improved performance in terms of redundancy-rate-distortion.

• IEIE Transactions on Smart Processing and Computing
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• v.4 no.1
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• pp.16-21
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• 2015

Most video services are transmitted in wireless networks. In a network environment, a packet of video is likely to be lost during transmission. For this reason, numerous error concealment (EC) algorithms have been proposed to combat channel errors. On the other hand, most existing algorithms cannot conceal the whole missing frame effectively. To resolve this problem, this paper proposes a new Adaptive Prediction Unit-based Motion Vector Extrapolation (APMVE) algorithm to restore the entire missing frame encoded by High Efficiency Video Coding (HEVC). In each missing HEVC frame, it uses the prediction unit (PU) information of the previous frame to adaptively decide the size of a basic unit for error concealment and to provide a more accurate estimation for the motion vector in that basic unit than can be achieved by any other conventional method. The simulation results showed that it is highly effective and significantly outperforms other existing frame recovery methods in terms of both objective and subjective quality.

• The KIPS Transactions:PartC
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• v.8C no.2
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• pp.182-188
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• 2001

이동 호스트에서 기지국으로의 데이터 전송 시 예상치 못한 기지국 전체 고장은 필연적으로 버퍼에 있는 데이터의 손실을 초래하고 적절한 손실 보상이 필요하다. 기지국의 고장시의 회복을 위한 기존의 기법들은 오버헤드가 많고 단순히 무선 링크 장애만을 고려하므로 기지 국 전체 고장에는 적합하지 않다. 유무선망 전체의 신뢰성 있는 전송을 위한 End to End 전송 방식도 비효율적으로 이동 호스트가 보상할 데이터 량을 알기 위해 필요한 기지국 버 퍼의 정확한 손실 정도를 알기 어렵다. 본 논문에서는 기존에 제안된 기법들의 문제점을 분 석하고 무선 ATM망에서 기지국 고장 시에 효율적으로 손실 보상을 하도록 하는 기법으로 CPS(Checkpoint Scheme)을 제안한다. CPS는 기지국이 버퍼의 출력 정보를 통보하여 고장 시에 이동 호스트가 seamless한 전송을 할 수 있도록 한다. 기존의 기법들과 시뮬레이션 및 비교 분석을 통하여 CPS의 효율을 증명한다.

• Journal of Institute of Control, Robotics and Systems
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• v.6 no.8
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• pp.629-637
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• 2000

Unbalance between user requirements and insufficient network resources makes a congestion. In the future since the communication networks will have very heavy traffic congestion will be more serious. The ATM networks was recommended to support the B-ISDN service for the future multimedia communication. In thie sense of congestion avoidance and recovery the ABR service category in ATM networks allows the feedback flow control mechanism to dynamically allocate the idle bandwidth of the network to users fairly and to control the network congestion rapidly In this paper we introduce a congestion control scheme using systematical approach to confirm robust stability with respect to unknown round trip delay for the network which has both unicast and multicast connections.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.215-218
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• 2006

A study was made to investigate microstructural evolution and mechanical properties of ultra-fine grained (UFG) pure-Ti produced by equal channel angular (ECA) pressings. The deformed structures were analyzed by finite element method and transmission electron microscopy with the increment of straining. After 4 isothermal ECA pressings, initial coarse grains ($30{\mu}m$) were significantly refined to ${\sim}0.3{\mu}m$ with homogeneous distribution of microstructure which was resulted from $180^{\circ}$ rotation of the sample between pressings. UFG pure-Ti exhibited the considerable improvement in yield strength while losing strain hardening capacity as compared to coarse grained microstructure at ambient temperature, which was mainly attributed to ultra-fine grain microstructure with non-equilibrium grain boundaries.

• Carbon letters
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• v.20
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• pp.10-18
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• 2016

Nanoporous carbon structures were synthesized by pyrolysis of grass as carbon precursor. The synthesized carbon has high surface area and pore volume. The carbon products were acid functionalized and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller, transmission electron microscopy, and Energy Dispersive X-ray microanalysis. Acid functionalized nanoporous carbon was explored for use in removal of toxic Cr(VI) ions from aqueous media. An adsorption study was done as a function of initial concentration, pH, contact time, temperature, and interfering ions. The experimental equilibrium data fits well to Langmuir isotherm model with maximum monolayer adsorption capacity of 35.335 mg/g. The results indicated that removal obeys a pseudo-second-order kinetic model, and that equilibrium was reached in 10 min. A desorption study was done using NaOH. The results of the present study imply that acid functionalized nanoporous carbon synthesized from grass is an efficient, renewable, cost-effective adsorbent material for removal of hexavalent chromium due to its faster removal rate and reusability.

• ETRI Journal
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• v.24 no.5
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• pp.405-408
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• 2002

In this paper, we discuss recovery schemes for errors occurring when image data encoded with variable length coding (VLC) is transmitted through additive white Gaussian noise (AWGN) and multiple-access interference in direct sequence code division multiple access (DS/CDMA) systems. VLC such as JPEG is so sensitive to channel errors that severe degradation in decoded images occurs even if only one or two bits have errors. This is due to the loss of synchronization at the image decoder. We propose a resynchronization scheme using a power allocation method in wireless DS/CDMA transmission. Through simulation, we know that the proposed method has a more robust resynchronization capability and higher objective and subjective quality than the conventional method.