• ETRI Journal
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• v.27 no.6
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• pp.697-707
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• 2005

This paper proposes a new design of directional couplers with high directivity for personal communication services (PCS) and International Mobile Telecommunications-2000 (IMT-2000). The directional coupler is used to check and verify the power, frequency, and antenna reflection of a signal at transmission stations for mobile communications. The performance requirements of directional couplers are a strong coupling to reduce the effect on the transmitted power and high directivity to suppress the interference of the reflected signals and reduce the errors in communication. So far, various architectures have been proposed to gain high directivity, and there have been many studies used to obtain a strong coupling. However, conventional architectures for high directivity and strong coupling have a directivity of only about 20 dB, and there have been difficulties to achieve the higher directivity of 30 dB suitable for PCS and IMT-2000. This paper proposes a new architecture of directional couplers based on a grounding composed of strip lines, and compares the test results of this directional coupler with conventional ones. The results show that the proposed directional coupler has a directivity of more than 30 dB and is adequate for PCS and IMT-2000.

• Journal of Communications and Networks
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• v.17 no.6
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• pp.568-581
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• 2015

Predicting locations of users with portable devices such as IP phones, smart-phones, iPads and iPods in public wireless local area networks (WLANs) plays a crucial role in location management and network resource allocation. Many techniques in machine learning and data mining, such as sequential pattern mining and clustering, have been widely used. However, these approaches have two deficiencies. First, because they are based on profiles of individual mobility behaviors, a sequential pattern technique may fail to predict new users or users with movement on novel paths. Second, using similar mobility behaviors in a cluster for predicting the movement of users may cause significant degradation in accuracy owing to indistinguishable regular movement and random movement. In this paper, we propose a novel fusion technique that utilizes mobility rules discovered from multiple similar users by combining clustering and sequential pattern mining. The proposed technique with two algorithms, named the clustering-based-sequential-pattern-mining (CSPM) and sequential-pattern-mining-based-clustering (SPMC), can deal with the lack of information in a personal profile and avoid some noise due to random movements by users. Experimental results show that our approach outperforms existing approaches in terms of efficiency and prediction accuracy.

• Advances in aircraft and spacecraft science
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• v.9 no.6
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• pp.525-536
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• 2022

The current state of telecommunications infrastructure in the Arctic does not allow providing a wide range of required services for people, businesses and other categories, which necessitates the use of non-traditional approaches to its organization. The paper proposes an innovative approach to building a combined communication network based on tethered high-altitude platform station (HAPS) located at an altitude of 1-7 km and connected via radio channels with terrestrial and satellite communication networks. Network configuration and composition of telecommunication equipment placed on HAPS and located on the terrestrial and satellite segment of the network was justified. The availability of modern equipment and the distributed structure of such an integrated network will allow, unlike existing networks (Iridium, Gonets, etc.), to organize personal mobile communications, data transmission and broadband Internet up to 100 Mbps access for mobile and fixed subscribers, rapid transmission of information from Internet of Things (IoT) sensors and unmanned aerial vehicles (UAV). A substantiation of the possibility of achieving high network capacity in various paths is presented: inter-platform radio links, subscriber radio links, HAPS feeder lines - terrestrial network gateway, HAPS radio links - satellite retransmitter (SR), etc. The economic efficiency of the proposed solution is assessed.

• Information and Communications Magazine
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• v.32 no.4
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• pp.16-22
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• 2015

유비쿼터스 정보 기술을 기반으로 다양한 업무 지원 기기간 네트워크를 형성하여 업무 처리를 지원하는 u-Office와, 지능화된 다양한 사물에 인터넷 연결성을 제공하여 지능적 서비스를 제공하는 Internet of Things(IoT)는 기하급수적으로 증가하는 다수의 객체간 통신을 수행하므로 네트워킹 자원의 최적화 기술이 필수로 뒷받침되어야 한다. 데이터 패킷의 오버헤드를 줄이고 통신 자원을 절약하기 위한 기술 연구는 다방면으로 진행되고 있으며, 특히 패킷의 오버헤드를 줄이고 통신 자원을 절약하는 패킷 헤더 압축 기술은 다양한 국제 표준이 개발되어 모바일 와이맥스(Mobile WiMAX), Long Term Evolution(LTE), IPv6 over Low power Wireless Personal Area Network(6LoWPAN) 등의 네트워크에 활용되고 있다. 본 고에서는 모바일 와이맥스, LTE, 6LoWPAN에서 각각 사용되는 패킷 헤더 압축 기술인 Payload Header Suppression(PHS), Robust Header Compression(ROHC), Header Compression(HC), Improved Header Compression(IPHC)의 개발 동향을 제시하고 각 기술의 특징을 비교 분석한다.

• Electronics and Telecommunications Trends
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• v.14 no.6 s.60
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• pp.127-133
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• 1999

위성이동개인휴대통신은 특정 지역이나 나라를 벗어나면 사용이 어려운 개인휴대통신 서비스의 지역적 한계를 해소한 글로벌 통신수단이다. GMPCS(Global Mobile Personal Communications by Satellite) 도입에 따른 단말기 자유이동에 관한 국제 양해 각서안이 ITU에서 채택되었다. GMPCS 기술이전의 중요성과 GMPCS 범위를 모든 종류의 위성시스템으로 확대하는 것이 주요한 내용으로 GMPCS의 조기실현, 국제협력, 범세계 서비스, 규제, 투자참여, 불법사용, 단말기의 자유이동, 보편적 접근, 상호접속, 추가적 협력 등에 대한 각국의 주권 및 국제적 의무사항 등을 설명한다. GMPCS 단말기의 자유 이동에 대한 양해각서 채택에 관한 내용으로 형식승인, 사용승인, 단말기 표시, 관세, MOU 검토, 통화 자료의 이용 등이 언급되었다. 본 논문에서는 자유롭게 국경선을 횡단하여 그들의 휴대를 수월하게 할 GMPCS 단말기의 형식승인에 대한 설비승인처리에 대한 표준규격과 국제간 상호인정협정을 위한 기술적 조건을 설명하고자 한다.

• 전자공학회논문지 IE
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• v.48 no.4
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• pp.19-24
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• 2011

Advances in mobile communications, portable computing and personal electronics have led consumers to demand large viewing area, bright, high resolution, compact and long life portable displays. Pico projectors are the latest technology to prove that big things often do come in small packages. Our goal in this paper was to implement a portable, low power, and highly adaptable miniature pico projector system. The pico projector is designed many functions of the pico projector solutions, multimedia, and T-DMB broadcasting.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.1090-1093
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• 2002

Location management schemes dealing with location information of moving terminals play an important role in the personal communications systems (PCS). Since the location management involves heavy signaling traffics to update the location information, reducing the location update cost becomes a critical research issue. This paper proposes a location management scheme which reduces the location update cost by employing the hierarchical structure in PCS environment. The paper also develops analytical models to evaluate the performance of the proposed scheme. The results obtained from the performance evaluation shows that the proposed scheme outperforms the conventional schemes in terms of the location update rates. Also, the difference in the performance becomes larger as the size of the location area (LA) becomes smaller and as the residual time of the mobile user becomes smaller.

• Electronics and Telecommunications Trends
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• v.35 no.4
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• pp.11-20
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• 2020

With the widespread use of high-performance electronics and mobile communications, electromagnetic interference (EMI) shielding has become crucial for protection against malfunctioning of electronic equipment and harmful effects to human health. In addition, smart sensor technologies will be rapidly developed in untact (non-contact) environments and personal healthcare fields. Herein, we introduce our recently developed technologies for flexible multifunctional EMI shielding, and highly sensitive wearable pressure-strain and humidity sensors realized using low-dimensional nanomaterials.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.230-233
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• 2003

In this paper, the wideband microstrip patch antennas for the Personal communications Service $(PCS\;:\;1750\~1870\;MHz)$ and International Mobile Telecommunications-2000 $(IMT-2000\;:\;1920\~2170\;MHz)$ dual band are studied. Experimental and simulation results on the dual band antenna are presented. Simulation results are in good agreement with measurements. The experimental and simulation results confirm the wideband characteristics of the antenna. The studied antenna satisfied the wideband characteristics that are required characteristics for above 420 MHz impedance bandwidth for the PCS and IMT-2000 dual band antenna. In this paper, through the designing of a dual band antenna, we have presented the availability for PCS & IMT-2000 base station antenna. An impedance bandwidth of $31\%(VSWR<1.5,\;615\;MHz)$ and a maximum gain of 7dBi can be achieved. The radiation pattern is stable across the passband.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.5
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• pp.148-154
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• 2008

In a ubiquitous computing environment, a ubiquitous smart space is required to help devices provide intelligent services. The smart space embedded with mobile devices should have the capabilities of collecting data and refining the data to contact. Unfortunately, the context information in a ubiquitous smart space has many ambiguous characteristics. Therefore, it is necessary to adapt a standard taxonomy for contact information in the smart space and to implement an inference technique of the context information based on taxonomy. Rule-based inference engine, such as CLIPS, Jess, was employed for providing situation-aware services. However, it is difficult for these engines to be used in resource limited mobile devices. In this paper, we propose a light-weight inference engine providing autonomous situation aware services in mobile environment. It can be utilized for personal mobile devices tuck as mobile phone, PMP and navigation. It can also support both generalized rules and specialized rules as using hierarchical taxonomy information.