• Journal of Advanced Navigation Technology
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• v.12 no.2
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• pp.154-163
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• 2008

In a mobile broadband wireless access (MBWA) network, many users access a base station (BS), which relays data transferred from high-speed wired network to low-speed wireless network. For this difference of their data rate, a BS suffers from the lack of its buffer space when many users run multiple applications at the same time, and thus packet losses occur. TCP, which guarantees end-to-end reliability, is used as transport protocol also in wireless networks. But TCP lowers their transmission rate incorrectly and frequently whenever packet losses occur. And they increase their transmission rate differently with each other; finally TCP throughput of each TCP flow varies largely, and then TCP fairness goes worse. In this paper, a scheme that controls packet transmission rate adaptively according to TCP flows' transmission rate, that prevents buffer overflows at BS, and that guarantees TCP fairness at a certain degree is proposed. As it is analyzed by simulations, the proposed scheme enhances TCP fairness by maintaining TCP throughput of each TCP sender similarly with each other.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.1
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• pp.33-39
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• 2002

In mobile communication systems, there are areas where signal coverage is not adequately accomplished by base stations. These areas may be underground parking zones, underground stores, tunnels, and insides of buildings, etc. In these areas, repeaters are broadly used as an economical solution. However, the capacity is decreased as the number of repeaters increases because the noise power that flows to a base station in the reverse link is proportional to the number of repeaters. The reduction of capacity in the reverse link is no longer negligible in the case that several tens or hundreds repeaters are connected to a base station. In this paper, we propose c repeater that is switched off automatically when there is no active user within its coverage. With the switching repeater, we can reduce the unnecessary noise level enhancement when there is no active user within the repeaters coverage. The reverse link capacity of a DS/CDMA system with AOS repeater is analyzed mathematically and compared with that without switching repeater. From the numerical results, noticeable improvement with the switching repeaters is shown.

• Journal of Navigation and Port Research
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• v.30 no.5 s.111
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• pp.351-356
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• 2006

In this paper, the high efficiency Doherty power amplifier has been designed and realized for microwave applications. The Doherty amplifier has been implemented using silicon MRF 281 LDMOS FET. The RF performances cf the Doherty power amplifier (a combination of a class AB carrier amplifier and a bias-tuned class C peaking amplifier) have been compared with those of a class AB amplifier alone. The realized Doherty power amplifier P1dB output power has 33dBm at 2.3GHz frequency. Also the Doherty power amplifier shows 11dB gain and -17.8dB input return loss at 2.3GHz to 2.4GHz. The designed Doherty amplifier has been improved the average PAE by 10% higher efficiency than a class AB amplifier alone. The Maximum PAE of designed Doherty power amplifier has been 39%.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2006.06b
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• pp.91-96
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• 2006

In this paper, the high efficiency Doherty power amplifier has been designed and realized for microwave applications. The Doherty amplifier has been implemented using silicon MRF 281 LOMOS FET. The RF performances of the Doherty power amplifier (a combination of a class AB carrier amplifier and a bias..tuned class C peaking amplifier) have been compared with those of a class AB amplifier alone. The realized Doherty power amplifier PldB output power has 33dBm at 2.3GHz frequency. Also the Doherty power amplifier shows 11dB gain and -17.8dB input return loss at 2.3GHz to 2.4GHz. The designed Doherty amplifier has been improved the average PAE by 10% higher efficiency than a class AB amplifier alone. The Maximum PAE of designed Doherty power amplifier has been 39%.

• Journal of Advanced Navigation Technology
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• v.14 no.6
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• pp.859-864
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• 2010

In the next generation system, a study on realization of Multi-Core system is in progress for applying it in multi service network. Therefore some mobile systems are expected to be appeared. These systems can support WiBro, WCDMA, CDMA, etc with single terminal. These systems have to support various FA using broadband frequency and hand over to other service network. Especially, in the telecommunication system composed of cell, the transmit power can be interference at adjacent system, has effect on system channel capacity and cell size. In this paper, we improve the unstable transmit power caused by unsettled system operation, propose the RF(Radio Frequency) Calibration method which can use the transmit power stably even during hand over between heterogeneous networks causing unstable power change. Also we used proposed method and analysed used electricity of system during hand over between heterogeneous networks.

• 한국HCI학회:학술대회논문집
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• 2008.02b
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• pp.262-267
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• 2008

애플의 iPhone 및 LG 의 프라다 폰 등을 기정으로 국내, 국외 제조사들은 전연 터치 스크린을 적용한 다양한 모바일 폰을 출시 또는 출시를 앞두고 있다. 모바일 폰에 적용되는 전면 터치 스크린은 4-방향키 기반의 일반적인 네비게이션의 제한에서 벗어나 보다 다양하고 진보된 스타일익 인터랙션을 가능하게 한다. 반면 이런 장점은 오히려 사용자에게 많은 학습을 요구하게 되며, 다른 제조사에서 제작된 하드웨어로 바꿀 때마다 또 다른 인터랙션 스타일을 학습하고 적응해야 하는 불편을 야기하게 만드는 원인이 될 수 있을 것이다. 따라서, 본 연구는 전면 터치 스크린 기반의 모바일 폰에 적용할 공통적이고 기본적인 인터랙션 스타일 가이드라인을 도출하는 것을 목적으로 한다. 이를 위해 기존에 출시된 터치 스크린이 일부 적용된 단말을 검토하여 기본적인 인터랙션 요소를 추출하였다. 그리고, 해당 요소에 적합한 인터랙션 스타일을 선정하기 위한 사용자 조사를 수행하고, 이를 기반으로 기본 인터랙션 가이드라인을 도출하였다. 본 연구에서 제안된 인터랙션 스타일 가이드라인은 다양한 제조사악 전면 터치 스크린 기반의 모바일 폰을 사용함에 있어 기본적인 요소에 대해서는 일관되고 예측이 가능한 사용 경험을 제공하도록 도움을 줄 수 있을 것이다.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.271-272
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• 2008

TD-SCDMA combines TDMA and CDMA components to provide more efficient use of radio resources, and includes a new feature called HSDPA (high-speed downlink packet access) in the R5 stage. The TD-HSDPA supports high-speed traffic with a shared channel, but its uplink mechanism causes feedback problem for scheduling. Since the base station of TD-SCDMA can estimate the location of mobile terminals precisely, it can also estimate the possible path loss. In this paper, the base station utilizes the estimated path loss for scheduling, which is related with CQI (channel quality indicator) values. The proposed mechanism can provide the TD-HSDPA scheduler with an intial CQI value for efficient transmission.

• Journal of Communications and Networks
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• v.7 no.2
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• pp.222-230
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• 2005

This article presents a field evaluation of an IP-based architecture for heterogeneous environments that has been developed under the aegis of the Moby Dick project, covering UMTS-like (universal mobile telecommunications system) TD-CDMA (time division-code division multiple access) wireless access technology, wireless and wired LANs. The architecture treats all transmission capabilities as basic physical and data-link layers, and replaces all higher-level tasks by IP-based strategies. The Moby Dick architecture incorporates mobile IPv6, fast handovers, AAA-control (authentication, authorisation, accounting), charging and quality of service (QoS) in an integrated framework. The architecture further allows for optimised control on the radio link layer resources. It has been implemented and tested by expert users, and evaluated by real users on field trials with multiple services available.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.04b
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• pp.1401-1404
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• 2002

무선인터넷의 활성화와 더불어 무선 전자상거래에 대한 관심이 고조되고 있다. 무선 전자상거래를 하기 위해서는 무선 환경에 적합한 보안/인증 및 지불/결제 솔루션이 필요하며 이러한 기술은 기존 유선인터넷에서 사용하고 있는 방식을 그대로 사용하기에는 어려움이 따른다. 본 연구에선 무선인터넷을 이용한 전자상거래에 안전하고 편리한 지불/결제를 위해 모바일 전자지갑(Mobile Wallet) 모듈의 설계와 이동전화단말기에 전자지갑 모듈을 구현함으로써 안전하고 편리한 지불/결제 솔루션을 제공한다. 모바일 전자지갑을 설계함에 있어 무선인터넷을 이용한 전자지갑 모듈의 동작 프로세스에 대해 기술하였으며, 단말기에 저장된 전자지갑 정보를 읽어와서 지불 및 배송에 필요한 정보에 대해 암호화와 전자서명을 수행하기 위한 전자지갑 용 WML Script 의 설계와 동작 프로세스에 대해 설명한다. 또한 이동전화 단말기에 전자지갑 모듈을 구현함에 있어 오프라인 전자지갑 모듈의 정보 입력과 모바일 전자지갑을 이용한 무선 전자상거래 서비스에 대해 단말 UI(User Interface) 기반으로 구현사례를 설명한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.467-470
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• 2013

Telecommunication cost have been increasing successively in Korean hoseholds and its level is high now. Even though here are a lot of issues related to the high bill of mobile telecommunication services, plausible solutions have not been provided yet. 99% of Koreans use mobile phones and it is the highest rate in the world, but bill is relatively high. This situation may be brought by the government policy selection that it supports three mobile telecom companies systems. Thus least efficient company should be supported to sustain by pricing policy and MVNO cannot come into the market. The government can make mobile pricing system consider revenue and cost only in proper manner and constrain marketing cost in the rational level. And it can reduce mobile bill levels and selection rights of consumers by restraining too much complicated bill system. Fairness of mobile phone bill levels could be achieves by mobile telecommunication structure improvement through active MVNOs and reduction of excessive marketing costs. Mobile bills can be made more acceptable if the base is measured rate system.