• KIPS Transactions on Software and Data Engineering
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• v.9 no.11
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• pp.377-386
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• 2020

Mobile cloud computing involves mobile or embedded devices as clients, and features small devices with constrained resource and low availability. Due to the fast expansion of smart phones and smart peripheral devices, researches on mobile cloud computing attract academia's interest more than ever. Computation offloading, or code offloading, enhances the performance of computation by migrating a part of computation of a mobile system to nearby cloud servers with more computational resources through wired or wireless networks. Code offloading is considered as one of the best approaches overcoming the limited resources of mobile systems. In this paper, we analyze the factors and the performance of code offloading, especially focusing on static program partitioning and data protection. We survey state-of-the-art researches on analyzed topics. We also describe directions for future research.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.12
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• pp.2210-2216
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• 2007

In this paper, triple-band plastic chip antennas for mobile terminal are investigated. Plastic chip antenna is composed of Foamex material with circle of PVC(Polyvilyl chloride). For its electric characteristics, the dielectric constant is 1.9, the insulation intensity is 112KV/cm. Plastic chip antennas are don't tend to break easily against to external shock, have more gain and efficiency than ceramic chip antennas. Triple-band plastic chip antennas of four type are implemented and experimented. From the experiments results, the antenna resonate at the triple-band, the gain of the antennas has about above -2dB, the pattern is ommidirectional the same as the conventional antennas. So, the antennas realized with Foamex material will be application for mobile phone antenna operated at the triple band which is cellular band and Korea-PCS band and ISM band or the antenna for other wireless communication system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.1
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• pp.75-80
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• 2021

Positioning technology is performing important functions in augmented reality, smart factory, and autonomous driving. Among the positioning techniques, the positioning method using beacons has been considered a challenging task due to the deviation of the RSSI value. In this study, the position of a moving object is predicted by training a neural network that takes the RSSI value of the receiver as an input and the distance as the target value. To do this, the measured distance versus RSSI was collected. A neural network was introduced to create synthetic data from the collected actual data. Based on this neural network, the RSSI value versus distance was predicted. The real value of RSSI was obtained as a neural network for generating synthetic data, and based on this value, the coordinates of the object were estimated by learning a neural network that tracks the location of a terminal in a virtual environment.

• Journal of KIISE:Information Networking
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• v.32 no.3
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• pp.415-426
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• 2005

Wireless internet, which becomes a hot social issue, has limitations due to the following characteristics, as different from wired internet. It has low bandwidth, frequent disconnection, low computing power, and small screen in user terminal. Also, it has technical issues to Improve in terms of user mobility, network protocol, security, and etc. Wireless internet server should be scalable to handle a large scale traffic due to rapidly growing users. In this paper, wireless internet proxy server clusters are used for the wireless Internet because their caching, distillation, and clustering functions are helpful to overcome the above limitations and needs. TranSend was proposed as a clustering based wireless internet proxy server but it has disadvantages; 1) its scalability is difficult to achieve because there is no systematic way to do it and 2) its structure is complex because of the inefficient communication structure among modules. In our former research, we proposed the All-in-one structure which can be scalable in a systematic way but it also has disadvantages; 1) data sharing among cache servers is not allowed and 2) its communication structure among modules is complex. In this paper, we proposed its improved scheme which has an efficient communication structure among modules and allows data to be shared among cache servers. We performed experiments using 16 PCs and experimental results show 54.86$\%$ and 4.70$\%$ performance improvement of the proposed system compared to TranSend and All-in-one system respectively Due to data sharing amount cache servers, the proposed scheme has an advantage of keeping a fixed size of the total cache memory regardless of cache server numbers. On the contrary, in All-in-one, the total cache memory size increases proportional to the number of cache servers since each cache server should keep all cache data, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.11A
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• pp.1076-1084
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• 2006

In this paper, we first review a concept of hybrid division duplexing (HDD) scheme, which has been proposed as a new type of duplexing scheme useful for a next generation mobile communication system and its implementation issues, including the unified radio resource management for HDD scheme. The HDD scheme maintains the advantages of both TDD and FDD at the same time while providing a useful structure to control the inter-cell interference, caused by an asymmetric traffic load of multimedia services over uplink and downlink in the TDD scheme. Employing two frequency bands, one for TDD scheme and the other for FDD scheme, uplink is operating under the TDD scheme only, while downlink is operating under the TDD or FDD scheme, depending on the location of mobile station. In the HDD scheme, therefore, it must determine a type of duplexing scheme to employ in the downlink and futhermore, a ratio of uplink and downlink duration to meet a given traffic load of asymmetric service, which requires some unified radio resource management for handling the subsequent inter-cell interference. In this paper, we propose a distributed adaptive control approach as a means of unified radio resource management for a HDD system that maximizes the overall system efficiency by fully utilizing the resource in TDD band, while minimizing the inter-cell interference.

• Journal of Advanced Navigation Technology
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• v.6 no.1
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• pp.37-43
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• 2002

This paper describes the performance evaluation and analysis of Wireless Local Area Network (W-LAN) in the 5 GHz ISM-band in compliance with IEEE 802.11a. At present, most W-LAN products are based on 2.4 GHz band, but low speed (11Mbps) has the limitation to serve systems demanding high-speed data transmission. To solve this problem, it is necessary to design next generation W-LAN system with 54Mbps in the 5GHz. It is sure that implementation of next generation W-LAN will bring competitive advantages. In particular, it will support telecommunications for high-speed mobile environments as well as for fixed places such as a school zone, a lecture room, a hospital and other premises. A few simulation methods are applied to more accurate and reliable performance analysis of next generation W-LAN. To verify if continuous data service is supported for a high-speed mobile notebook, multi-path fading channels between wireless Access Point (AP) and wireless Network Interface Card (NIC) are modeled. In addition, low interference is analyzed via convolutional codes and Orthogonal Frequency-Division Multiplexing (OFDM). Also, to obtain reliable Bit Error Rate (BER), a single tap Least Mean Square (LMS) equalizer is applied. Given the above simulation, next generation W-LAN is an ideal solution for continuous data transmission in high-speed mobile environments.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.169-177
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• 2007

Existing wireless access (mobile) routers are based commonly on the network address and port translation (NAPT) technique which permits simultaneously sharing a subscriber's connection to the network with multiple users. However, the NAPT architecturally makes the users invisible on the network side, thus becoming a user-oriented connection technique. In this paper, we propose a novel service provider-oriented unlicensed nomadic access relay station (WiNNERS) for helping wireless broadband network service providers to make their business more lucrative by accommdating unlicensed band users as subscribers into their network. The WiNNERS offers service providers the capability to directly manage each of the unlicensed band users at the network side. This direct management allows the service providers to flexibly and simply handle QoS, access control, and billing for each user. In order to distinguish each of the unlicensed band users the WiNNERS constructs a virtual tunnel from each user's terminal to the network access router using connection identifiers which is defined for service flow management within the WiBro system, Consequently, our proposed service provider-oriented relay station can be included into the WiBro network system with minimum modifications.

• The KIPS Transactions:PartB
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• v.12B no.6 s.102
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• pp.679-684
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• 2005

There are a few representative wireless network access technologies used widely. WWAN is celluar based telecommunication networks supporting high mobility, WLAN ensures high data rate within hotspot coverage, and WDMB support both data and broadcasting services correspondingly. However, these technologies include some limitations especially on the mobility, data rate, transmission direction, and so on. In order to overvome these limitations, there are various studies have been proposed in terms of 'Vortical Handoff' that offers seamless connectivity by switching active connection to the appropriate interface which installed in the mobile devices. In this paper, we propose the interface selection algorithm and network architecture to maximize the life time of entire system by minimizing the unnecessary energy consumption of another interfaces such as WLAN, WDMB that are taken in the user equipment. In addition, by using the results of analyzing multiple types of traffic and managing user buffer as a metric for vertical handoff, we show that the energy efficiency of our scheme is $75\%$ and $34\%$ than typical WLAN for WDMB and WLAN preferred schemes, correspondingly.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.12
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• pp.55-63
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• 2015

Recently, terroristic threats using a radio controlled improvised explosive device (RCIED) that is remotely controlled and exploded have been increased around the world. In order to prevent the explosion of an RCIED, jamming techniques that interrupt an RCIED receiver can be used, so that the receiver can not demodulate the trigger code. Conventional jamming technique is a type of active barrage jamming that always emits the noise jamming signal for all the frequency band. However, it needs large power consumption and thus is limited in operation time for a vehicle. In order to overcome the shortage of the active barrage jamming, reactive jamming technique has drawn attention. In reactive jamming, all the frequency band is firstly scanned, and then if any trigger signal exists, one emits the jamming signal to the corresponding frequency band. Therefore, the reactive jamming is superior to the active barrage jamming in terms of power efficiency. However, a reactive jammer emits a jamming signal only after the trigger signal is intercepted, which means that the jamming signal may be late for interrupting an RCIED receiver. In this sense, it is needed to evaluate a delay in an RCIED receiver. To achieve this, we analyze the reaction time and present the simulation result for jamming performance of reactive jamming against an RCIED using mobile devices.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.11A
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• pp.1661-1671
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• 2000

본 고에서는 한국통신(Korea Telecom) IMT-2000 시험시스템(이하: Trial system 라고 함) 단말기용 전력증폭단으로 적용하기 위한 다단구동증폭기 및 전력증폭기를 GaAs MMIC로 설계 구현하는 기술을 제시하였다. 설계된 구동증폭기는 3단으로구성하여 RF(Radia Frequency) 송신신호(1955$\pm$70MHz)대역에서 2단 (중간단)의 이득 조정범위가 40 dB이상이 될 수 있도록 능동부품인 MESFET를 Cascade 형으로 구성하고 MESFET의 게이트(gate)에 조정전압을 인가하는 증폭기를 설계하여 GaAs MMIC화 1 침(크기4$\times$5 mm)으로 제작하였다. 아울러, 본 논문에서는 제시한 구동증폭기는 동작주파수 대역폭 범위기 3.5배이고 출력전력은 15dBmm 이며, 출력전력이득이 25~27dB이고 반사계수는 -15~20dB이며 이득평탄도 3dB(동작주파수 대역폭내)로써 Trial system용 단말기의 최종단인 전력증폭단의 출력단 특성을 효과적으로 나타내었다. 그리고, 전력 증폭기는 2개의 입력단에서 출력되는 신호를 분배하는 전력분배기와 병렬구조인 4개의 증폭단에서 출력되는 출력신호를 외부에서 접속하는 전력결합기를 접소하여 구성하였으며 RF(Radio Frequency) 주파수(1955 $\pm$70NHz)에서 대역폭을 4배로 설계하여 광대역인 대역폭을 구현하였고 출력전력은 570mW이며, 출력부가효율(PAE; Power Added Efficency)가 -15$\pm$20dB이고, 이득 평탄도(Gain flatness)는 동작주파수 대역내에서 0.5dB이며 입출력 전압정재파비(Input & Output VSWR)가 13이하인 고출력 전력증포기를 GaAs MMIC화 1칩 (크기; 3$\times$4mm)으로 제작하였다.의 다양성이나 편리성으로 변화하는 것이 국적을 바꾸는 것보다 어려운 시 대가 멀지 않은 미래에 도래할 것이다. 신세기 통신 과 SK 텔레콤에는 현재 1,300만명이 넘 는 고객이 있으며. 이들 고객은 어 이상 음성통화 중심의 이동전화 고객이 아니라 신세기 통신과 SK텔레콤이 함께 구축해 나갈 거대란 무선 네트워크 사회에서 정보화 시대를 살아 갈 회원들이다. '컨텐츠의 시대'가 개막되는 것이며, 신세기통신과 SK텔레콤은 선의의 경쟁 과 협력을 통해 이동인터넷 서비스의 컨텐츠를 개발해 나가게 될 것이다. 3배가 높았다. 효소 활성에 필수적인 물의 양에 따른 DIAION WA30의 라세미화 효율에 관하여 실험한 결과, 물의 양이 증가할수록 그 효율은 감소하였다. DIAION WA30을 라세미화 촉매로 사용하여 아이소옥탄 내에서 라세믹 나프록센 2,2,2-트리플로로에틸 씨오에스터의 효소적 DKR 반응을 수행해 보았다. 그 결과 DIAION WA30을 사용하지 않은 경우에 비해 반응 전환율과 생성물의 광학 순도는 급격히 향상되었다. 전통적 광학분할 반응의 최대 50%라는 전환율의 제한이 본 연구에서 찾은 DIAION WA30을 첨가함으로써 성공적으로 극복되었다. 또한 고체 염기촉매인 DIAION WA30의 사용은 라세미화 촉매의 회수 및 재사용이 가능하게 해준다.해준다.다. TN5 세포주를 0.2 L 규모 (1 L spinner flask)oJl에서 세포간의 응집현상 없이 부유배양에 적응,배양시킨 후 세포성장 시기에 따른 발현을 조사한 결과 1 MOI의 감염조건 하에서는 $0.6\times10^6$cell/mL의 early exponential시기의 세포밀도에서 72시간 배양하였을 대 최대 발현양을 나타내었다. 나타내었다. $\beta$4 integrin의 표현이 침투 능력을 높이는 역할을 하나 이때에는 laminin과 같은 리간드와의 특이