• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.2
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• pp.323-335
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• 2015

Mobile healthcare is a fusion of information technology and biotechnology and is a new type of health management service to keep people's health at anytime and anywhere without regard to time and space. The WBAN(Wireless Body Area Network) technology that collects bio signals and the data analysis and monitoring technology using mobile devices are essential for serving mobile healthcare. WBAN consisting of users with mobile devices meet another WBAN during movement, WBANs transmit data to the other media. Because of WBAN conflict, several nodes transmit data in same time slot so a collision will occur, resulting in the data transmission being failed and need more energy for re-transmission. In this thesis, we proposed a MAC protocol for WBAN with mobility to solve these problems. First, we proposed a superframe structure for WBAN. The proposed superframe consists of a TDMA(Time Division Muliple Access) based contention access phase with which a node can transmit data in its own time slot and a contention phase using CSMA/CA algorithm. Second, we proposed a network merging algorithm for conflicting WBAN based on the proposed MAC protocol. When a WBAN with mobility conflicts with other WBAN, data frame collision is reduced through network reestablishment. Simulations are performed using a Castalia based on the OMNeT++ network simulation framework to estimate the performance of the proposed superframe and algorithms. We estimated the performance of WBAN based on the proposed MAC protocol by comparing the performance of the WBAN based on IEEE 802.15.6. Performance evaluation results show that the packet transmission success rate and energy efficiency are improved by reducing the probability of collision using the proposed MAC protocol.

• Journal of KIISE:Computing Practices and Letters
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• v.16 no.3
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• pp.336-340
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• 2010

Flash storages are prevalent as portable storage in computing systems. When we consider the detachability of Flash storage devices, data integrity becomes an important issue. To assure extreme data integrity, file systems synchronously write all file data to storage accompanying hot write references. In this study, we concentrate on the effect of hot write references on Flash storage, and we consider the effect of absorbing the hot write references via nonvolatile write cache on the performance of the FTL schemes in Flash storage. In 80 doing, we quantify the performance of typical FTL schemes for workloads that contain hot write references through a wide range of experiments on a real system environment. Through the results, we conclude that the impact of the underlying FTL schemes on the performance of Flash storage is dramatically reduced by absorbing the hot write references via nonvolatile write cache.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2006.11a
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• pp.93-103
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• 2006

소비자의 하이테크 서비스 가입 이후 행태를 살펴보면, 가입자들은 서비스를 실제로 사용하기도 전에 가입 해지결정을 내리기도 한다. 최근 미국의 기간통신회사에서 출시된 인터넷전화 서비스의 경우, 출시 후 1년 반 동안 이탈한 고객 중 무려 60%정도가 서비스를 실제로 사용하기 전 상태인 네트워크 및 시스템이 준비되는 동안이나 소비자가 가정에서 전화기 연결용 어댑터를 설치하는 단계에서 이탈한 것으로 나타났다. 이와 같은 가입초기 고객의 이탈은 기업에게 고객획득과정에서 지출된 마케팅비용의 손실 및 미래의 매출감소뿐만 아니라, 기 가입자를 통한 미래의 가입 희망자에게 미칠 수 있는 긍정적 구전효과와 같은 간접효과에 대한 손실을 의미한다. 하지만 하이테크 서비스에 대한 소비자의 가입 후 행태에 대한 기존연구는 고객불평 연구, 서비스 사용 후 발생하는 정상적 이탈행태(normal churn)에 대한 연구, 또는 탐색적 연구를 제외하면 매우 부족하다. 더욱이 하이테크서비스의 특성을 고려한 서비스 출시초기에 소비자의 가입직후 해지결정에 대한 결정요인 연구는 그 필요성에 비해 연구가 전무하다시피한 실정이다. 본 연구에서는 하이테크 서비스에 대한 소비자의가입시점과 실제 사용시점 사이에 발생하는 소비자의 이탈행태를 이탈시점에 따라 '가입직후 이탈(immediate churn)' 과 '가입 후 이탈(earlychurn)'로 정의한 후, 특히 가입직후 고객의 이탈행태를 설명하기 위해 하이테크 서비스에 대한 소비자의 이전 사용경험정도와 서비스에 대한 정보를 획득한 채널의 정보전달 풍부성 등을 연구모형에 포함하였다. 이 기간 동안에 기업은 서비스 제공에 필요한 부수적인 기기 제공 및 서비스 준비 등을 수행하지만, 동시에 소비자는 여러가지 이유로 가입결정을 제고할 수도 있게 된다. 제안된 연구모형에 대한 실증분석을 위해 미국 유수의 기간통신회사에서 2004년 출시된 인터넷전화(Voice over Internet Protocol: VoIP)서비스에 가입한 12,000여명 의 고객 프로파일과 서비스사용 데이터를 활용하였다. 분석결과 가입자의 하이테크 서비스에 대한 사용경험정도가 낮을수록 서비스 가입직후 바로 해지하는 경향을 보였다. 하지만 하이테크 서비스에 대한 이전 사용경험이 낮은 경우라도, 가입 후서비스를 실제로 사용하였다면 서비스에 대한 가입해지 경향은 더 이상 나타나지 않았다. 이는 가입자의 하이테크 서비스에 대한 이전 사용경험정도가 가입직후 해지에만 영향을 미치는 요인임을 보여준다. 또한 매체의 정보전달 풍부성 (media richness)이 상대적으로 높은 소매점이나 웹사이트를 통해 서비스에 가입한 소비자일수록 가입 직후뿐만 아니라 서비스사용 이후에도 낮은 해지성향을 나타냈다. 이러한 분석결과를 바탕으로 인터넷전화 서비스에 적합한 고객지원 프로그램 설계와 마케팅 매체선정과 관련한 전략적 시사점을 도출한다. 그리고 국내에서 최근 이슈가 되고 있는 차세대 무선인터넷 서비스인 와이브로 출시에 따른 마케팅 및 고객관리와 관련된 시사점을 논의한다.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.8 no.6
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• pp.121-130
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• 2009

In this paper, Gaussian probability distribution model based multi-sensor data fusion algorithm is proposed for a vehicular location awareness system. Conventional vehicular location awareness systems are operated by GPS (Global Positioning System). However, the conventional system is not working in the indoor of building or urban area where the receiver is difficult to receive the signal from satellites. A method which is combined GPS and UWB (Ultra Wide-Band) has developed to improve this problem. However, vehicular is difficult to receive seamless location information since the measurement systems by both GPS and UWB convert the vehicle's movement information separately at each sensor. In this paper, normalized probability distribution model based Hybrid UWB/GPS is proposed by utilizing GPS location data and UWB sensor data. Therefore the proposed system provides information with seamless and location flexible properties. The proposed system tested by Ubisense and Asen GPS in the $12m{\times}8m$ outdoor environments. As a result, the proposed system has improved performance for accurateness and connection ability between devices to support various CNS (Car Navigation System).

• Korean Business Review
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• v.17 no.2
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• pp.203-228
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• 2004

This dissertation investigated the evaluation model of IT Service quality: concentrated on the quality components in mobile communication service. Today, mobile communication service is changing dramatically. The first and second generation's mobile communication services were designed for voice and SMS(Short Message Service). However, while the mobile communication industry grows, the mobile technology made more services available for customers. Customers' changing needs brought a new opportunities to the market. Now, mobile communication service is facing a new era as multi-functioning, multimedia service, and high speed data transfer service are being introduced. There has been a lot of theoretical literature on service quality components of mobile communication, but most of the literature was focused on the voice service and SMS(1st and 2nd generation). As mobile communication service evolves, the components may have to be altered or rebuilt. To identify which service quality components ought to be utilized, prior studies on service quality components, service quality, and customer satisfaction were reviewed. Also, a survey was conducted on the various aspects of mobile communication service. This study suggests 6 components of service quality: those are supporting facilities, cellular phone(facilitating goods), quality of the voice service(explicit service), supplementary services, supporting services, and cost. Empirical results supported that all of these components are proven as the service quality components, but, with regards to customer satisfaction, only cellular phone(facilitating goods) and supplementary services are effective. As previously stated, the relationship between service quality and customer satisfaction is also proven. This study is a point of departure for the success of upcoming generation's mobile communication service. It identifies what is valuable from the customer's point of view. Furthermore, it suggests some ideas to prepare for future market opportunities.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.4
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• pp.9-16
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• 2015

Quick and safe message transmission is an important research topic of vehicular ad hoc networks (VANET). Most studies assume that the periodic broadcast of beacon-frames between vehicles increases the safety of the driver. In this paper, we propose a medium access control (MAC) protocol and location-based clustering for the VANET to support reliable data transfer. In our proposal, the cluster heade (CH) manage the access and allocate the resources of the node. Our proposal uses simulation to confirm the reduction of the transmission delay and the collision rate of the signal.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.4 no.1
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• pp.28-37
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• 1993

The future Personal Communication Service(PCS) is the total personal information communication service to satisfy the importance of information in a highly information - oriented society. Compared with the conventional communication method, it is necessary to provide considerable intelligence to the commu- nication network in order to implement the PCS which guarantees the mobility of each individual. Consequen- tly, the PCS needs a fast large database system which stores the information of each individual. To achieve this goal, this paper presents the parallel implementation of deductive database systems as a main - memory database system.

• Proceedings of the Korean Information Science Society Conference
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• 2006.10d
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• pp.782-785
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• 2006

셀 내의 모바일 노드들의 수가 많고 셀 간의 이동이 빈번한 고속 모바일 네트워크에서는 기존 802.11 프로토콜로는 좋은 성능을 보장할 수 없다. 셀 내에 새로 진입한 노드들은 네트워크에 참여하기 위해 자신의 존재 여부를 알려야 한다. 802.11 표준에서는 이러한 선행되어야 할 작업을 스캐닝, 인증, 결합의 3가지 단계로 규정한다. 이 등록 작업은 셀 내의 다른 데이터 패킷을 보내려는 노드들과의 경쟁을 통해 이루어진다. 그러므로 셀 내의 노드 수가 많을 경우 기본적인 통신을 위해 선행되어야 할 등록 작업이 지연될 수 있다. 802.11 표준에서는 DCF 방식을 기본 매체 접근 프로토콜로 한다. DCF는 BEB (Binary Exponential Backoff) 알고리즘을 기반으로 한다. BEB 알고리즘의 여러 문제점[5]으로 이를 대체할 알고리즘이 연구되어왔으며, 그룹화를 통해 경쟁하는 노드의 수를 줄이는 방법도 고려되었다. 본 논문에서는 802.11의 성능 평가를 위한 모델링에 Markov chain을 이용한 논문[1]을 기반으로 하나의 노드가 등록 작업에 소요하는 평균 시간을 해석적으로 계산하였다. 셀 내의 전체 노드 수에 증가함에 따라 등록 시간을 계산하고, 직접 시뮬레이션을 통해 수식으로 얻어진 결과와 비교하였다. 또한 그룹화를 시뮬레이션 하여 전체 노드 수에 따라서 적절한 그룹 수의 조정이 그룹화하지 않았을 경우보다 더 나은 성능을 보여줄 수 있다는 것을 보였다.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.6
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• pp.1151-1158
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• 2020

In order to investigate the speed profile of data I/O of HDD, we have developed an utility program. The application to HDD reveals the detail properties of the speed profile of HDD and the relation between the cylinder structure of HDD and the velocity profile. For the extent application, the experiment of the large volume storage was performed, and the profile of SSD media, which is known as the new rapid media, was measured. The new M.2 NVME SSD, which has the ability of over 10Gbps, we can compare the velocities between cp under linux O/S and the utility, and shows that the performance of the utility can be reliable.

• Convergence Security Journal
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• v.13 no.3
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• pp.33-38
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• 2013

Security between mobile nodes and efficient communication is one of the most important parts of the MANET. In particular, the wireless network is significantly higher for the attack threats because of collaborative structure for open communication media and communication. However, application of existing security mechanisms and intrusion detection system is not easy due to the characteristics of MANET. It is because collection and integration of adult data by the dynamic topology due to the mobility of nodes and many network sensors is difficult. In this study, we propose cooperative security system technique that can improve the reliability based on authentication assessing confidence about the whole nodes which joins to network and detect effectively this when intrusion occurs. Cluster head which manages the cluster performs CA role for the certificate issue and the gateway node performs role of intrusion detection system. Intrusion detection is performed by cooperating with neighboring nodes when attack is not detected in one intrusion detection node. The performance of the proposed method was confirmed through experiments comparing with the SRP technique.