• Journal of KIISE:Software and Applications
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• v.37 no.5
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• pp.341-353
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• 2010

Mobile Internet Device (MID) allows users to flexibly use various forms of wireless internet such as Wi-Fi, GSM, CDMA, and 3G. Using such Internet, MID users can utilize application services. MID usage is expected to grow due to the benefits of portability, Internet accessibility, and other convenience. However, it has resource constraints such as limited CPU power, small memory size, limited battery life, and small screen size. Consequently, MIDs are not capable to hold large-sized complex applications and to process a large amount of data in memory. An effective solution to remedy these limitations is to develop cloud services for the required application functionality, to deploy them on the server side, and to let MID users access the services through internet. A major concern on running cloud services for MIDs is the potential problems with low Quality of Service (QoS) due to the characteristics of MIDs. Even measuring the QoS of such services is more technically challenging than conventional quality measurements. In this paper, we first identify the characteristics of MIDs and cloud services for MIDs. Based on these observations, we derive a number of quality attributes and their metrics for measuring QoS of mobile services. A case study of applying the proposed quality model is presented to show its effectiveness and applicability.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.355-362
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• 2012

Remaining useful life(RUL) prediction of a system is important in the prognostics field since it is directly linked with safety and maintenance scheduling. In the physics-based prognostics, accurately estimated model parameters can predict the remaining useful life exactly. It, however, is not a simple task to estimate the model parameters because most real system have multivariate model parameters, also they are correlated each other. This paper presents representative methods to estimate model parameters in the physics-based prognostics and discusses the difference between three methods; the particle filter method(PF), the overall Bayesian method(OBM), and the sequential Bayesian method(SBM). The three methods are based on the same theoretical background, the Bayesian estimation technique, but the methods are distinguished from each other in the sampling methods or uncertainty analysis process. Therefore, a simple physical model as an easy task and the Paris model for crack growth problem are used to discuss the difference between the three methods, and the performance of each method evaluated by using established prognostics metrics is compared.

• Journal of the Korea Society for Simulation
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• v.19 no.4
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• pp.11-19
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• 2010

ZigBee is a standard for wireless personal area networks(WPANs) based on the IEEE 802.15.4 standard. It has been developed for low cost and low power consumption. There are two alternative routing schemes that have been proposed for the ZigBee standard: Ad-hoc On-Demand Distance Vector(AODV) and tree routing. The tree routing forwards packets from sensors to a sink node based on the parent-child relationships established by the IEEE 802.15.4 MAC topology formation procedure. In order to join the network, a sensor node chooses an existing node with the strongest RSSI(Received signal strength indicator) signal as a parent node. Therefore, some nodes carry a large amount of traffic load and exhaust their energy rapidly. To overcome this problem, we introduce a new metric based on link quality and traffic load for load balancing. Instead of the strength of RSSI, the proposed scheme uses the new metric to choose a parent node during the topology formation procedure. Extensive simulation results using TOSSIM(TinyOS mote SIMulator) show that the CFR scheme outperforms well in comparison to the conventional tree routing scheme.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.3
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• pp.55-61
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• 2017

In DVB-S3 standard of satellite broadcasting systems, FTN technique is applied to LDPC codes with (1+7) PSK modulation. In standard, BICM-ID and BCJR decoding method are considered to alleviate performance degradation due to FTN processing. BICM-ID method improves performance by calculating a new LLR from hard-decision value of decoder output. BCJR also improves performance by calculating forward and backward matrix each other. However these two methods require high computational complexity. Therefore this paper proposed modified decoding method in order to reduce computational complexity without performance degradation.

• Journal of IKEEE
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• v.4 no.2 s.7
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• pp.257-265
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• 2000

Turbo Code decoder is an iterate decoding technology, which extracts extrinsic information from the bit to be decoded by calculating both forward and backward metrics in each decoding step, and uses the information to the next decoding step. Viterbi decoder, which is for a convolutional code, runs continuous mode, while Turbo Code decoder runs by block unit. There are algorithms used in a decoder : which are MAP(maximum a posteriori) algorithm requiring very complicated calculation and SOVA(soft output Viterbi algorithm) using Viterbi algorithm suggested by Hagenauer, and it is known that the decoding performance of MAP is better. The result of this make experimentation shows that the performance of SOVA, which has half complex algorithm compare to MAP, is almost same as the performance of MAP when the SOVA decoding performance is supplemented with Robust equalization techniques.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2008.11a
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• pp.31-34
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• 2008

양방향 중계 채널(two-way relay channel)은 2명의 사용자가 중계기(relay)의 도움을 받아 서로 정보를 주고받는 통신 채널이다. 중계기에서는 각각의 사용자로부터 독립적으로 수신한 두 데이터 패킷에 네트워크 코딩 기법을 적용하고, 이를 통해 만든 패킷을 두 사용자에게 동시에 전송한다. 따라서 양방향 중계 채널에서는 기존의 협력 통신에 비해 보다 효율적인 자원의 사용이 가능하다. 한편, 다중 중계기 환경에서의 중계기 선택 기반 전송 방식은 시스템의 전력 제한(power constraint), 전송 패킷의 동기화(synchronization) 문제 등을 고려할 때 다중 중계기 기반 전송 방식보다 우수한 성능을 얻을 수 있다. 본 논문에서는 양방향 다중 중계기 채널에서 중계기 선택 기법을 제안한다. 양방향 중계 채널에서는 수신한 두 신호의 결합을 위해 중계기에서 네트워크 코딩 기법을 적용함으로써 중계기의 부담이 보다 증가하는 특징이 있다. 또한, 중계기는 신호 전송 시 두 사용자 모두에게 전송하게 되고 이로 인해 두 수신지와의 채널 조건을 모두 고려하여야 한다. 따라서 중계기 선택은 데이터 패킷의 전송이 시작되기 전에 분산된 방식(distributed method)으로 이루어지며, 각각의 사용자와 중계기 간 일시적(instantaneous) 채널 이득을 바탕으로 사용자-사용자 간(end-to-end) 경로 조건의 최대값을 계산하는 메트릭(metric)을 중계기 선택 기준으로 사용한다. 모의실험을 통해 제안된 중계기 선택 기법이 중계기의 개수에 해당하는 다이버시티 이득을 얻을수 있음을 보여준다.

• The KIPS Transactions:PartD
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• v.10D no.4
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• pp.689-696
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• 2003

Criticality prediction models that determine whether a design entity is fault-prone or non fault-prone are used for identifying trouble spots of software system in analysis or design phases. Many criticality prediction models for identifying fault-prone modules using complexity metrics have been suggested. But most of them need training data set. Unfortunately very few organizations have their own training data. To solve this problem, this paper builds a new prediction model, KSM, based on Kohonen SOM neural networks. KSM is implemented and compared with a well-known prediction model, BackPropagation neural network Model (BPM), considering internal characteristics, utilization cost and accuracy of prediction. As a result, this paper shows that KSM has comparative performance with BPM.

• The Journal of the Korea Contents Association
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• v.9 no.11
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• pp.63-73
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• 2009

Architecture base mechanism centers to construct software system. There is construction of successful software system how firmly define software. Reason that architecture base software is important is used and expresses early design decision item of system and is because reusability is possible by means of communication between comprehension person concerned. Analyzed special quality of pattern and importance of architecture and general requirement and portability and consider ISO/IEC 9126 and ISO/IEC 14598 and propose system and Metrik in this research. Also, do defect particulars and efficiency test that test according to examination formality of architecture base software and analyzed result.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9C
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• pp.871-876
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• 2005

In this paper, we propose an improved partial response maximum likelihood (PRML) detection scheme that has an adaptive equalizer and can be applied in the asymmetric optical recording system with high-density. We confirmed that the proposed PRML detector improves detection performance. In addition, we implemented the detector by Verilog HDL. The adaptive equalizer is composed of tap coefficient updating unit using LMS algorithn and FIR filter. FIR filter is implemented by the transposed direct form architecture for high speed operation. Viterbi detector is implemented by the register exchange method.

• The KIPS Transactions:PartA
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• v.10A no.5
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• pp.463-468
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• 2003

The Internet, especially the mobile Internet influences enormously in many areas in human societym espeially in terms of the exchanging speed of knowledge and information. This new society of knowledge and information will introduce many new types of services based on valuable knowlwdge and information. Among many new services in this mobile computing environment, the real-time worldwide korean information networking service using the Korean characters invented by the mobile computing environment, the real-time worldwide Korean information networking service using the Koean characters invented by the King Sejong is possible ubiquitously with wired and mobile Internet. We studied the user interface with Korean characters in the mobile computing environment, and introduce the useful results with new metrics of performance analysis after real implementation for real-time Korean information networking using Korean domain names.