• The Journal of Korean Institute of Communications and Information Sciences
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• v.11 no.5
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• pp.349-359
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• 1986

This paper is the basic research to identify automatically signals that are less than the bandwidth of 200Hz in shortwave band between 3 to 7 MHz and rarely appear. In order to do so, first, we describe the Detection and Estimation method of testing for the presence of absence about OOK signals of odB degree in 100KHz bandwidth. In the course of Detection and Estimation, it has decided the presence of OOK modulation Signal in additive noise to about 77% using LOD and E-C and about 90% using pattern model method of correlation function.

• The Journal of Korean Association of Computer Education
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• v.11 no.5
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• pp.47-55
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• 2008

The Internet is one of the most infrastructure for information technology in school education. Providing the Internet with a proper bandwidth is an important element for efficient school education for information technology, especially because several instructional models based on new Internet technologies are under development. To support these instructional models, it is important for the schools to provide the proper Internet bandwidth wherever necessary. In this paper, the amount and pattern of internet usage in school were analyzed. Based on this analysis, we propose how to figure out a proper bandwidth for a different ladder of schools.

• Journal of Industrial Technology
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• v.27 no.A
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• pp.131-139
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• 2007

The recent advance in wireless network technologies has enabled the streaming media service on the mobile devices such as PDAs and cellular phones. Since the wireless network has low bandwidth channels and mobile devices are actually composed of limited hardware specifications, the transcoding technology is needed to adapt streaming media to given mobile devices. Futhermore owing to the diversity of bandwidth in the wireless network by reason of mobile users' movements and environments, it is difficult to provide stable QoS. In this paper, the autonomic multimedia transcoding system is proposed in order for users to provide network adaptive QoS. Our proposed system is based on the estimation of available bandwidth in wireless network for seamless multimedia streaming service. The proposed system is designed and implemented for various mobile clients. In experiments, we evaluate its seamless multimedia streaming and the adaptation transcoding bit rate according to the changes of bandwidth in wireless network.

• ETRI Journal
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• v.37 no.4
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• pp.677-684
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• 2015

Recently, orthogonal frequency-division multiplexing (OFDM) was applied to VLC systems owing to its high rate capability. On the other hand, a real-valued unipolar OFDM signal for VLC significantly reduces bandwidth efficiency. For practical implementation, channel estimation is required for data demodulation, which causes a further decrease in spectral efficiency. In addition, the large fluctuation of an OFDM signal results in poor illumination quality, such as chromaticity changes. This paper proposes a spectrally efficient method based on a hidden-pilot-aided precoding technology for VLC with less flickering than a conventional OFDM-based method. This approach can obtain channel information without any loss of bandwidth efficiency while ensuring illumination quality by reducing the flickering effect of an OFDM-based VLC. The simulation results show that the proposed method provides a 6.4% gain in bandwidth efficiency with a 4% reduction in flicker compared to a conventional OFDM-based method.

• ETRI Journal
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• v.32 no.4
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• pp.603-606
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• 2010

In this letter, we propose a channel estimation algorithm based on incremental pilots. These are pilots additionally inserted after puncturing the modulated orthogonal frequency division multiplexing (OFDM) symbols to enhance channel estimation performance without lowering bandwidth efficiency. A low-density parity-check code puncturing scheme is also proposed to prevent the performance degradation due to the codeword bit loss caused by punctured OFDM symbols.

• Journal of IKEEE
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• v.22 no.3
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• pp.599-604
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• 2018

A Stepped Frequency Radar(SFR) is a method that realizes high resolution range estimation by increasing the frequency of transmission pulses at regular intervals to generate a wide synthetic bandwidth. However, in the case of a moving target, accurate range estimation becomes difficult due to the range-Doppler coupling. In this paper, the process of high resolution range estimation by compensation of the range-Doppler coupling with estimated velocity of the moving target using the SFR waveform with Coherent Pulse Train(CPT) is analyzed and it was verified through simulation.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.4 no.1 s.6
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• pp.63-71
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• 2005

This paper proposes the channel estimation method robust to severe frequency selective fading channels in O%M system using wide bandwidth for the high data rate transmission. DDCE, which uses data between the high correlated symbols, is usually used for channel estimation in the slow fading channels. DDCE can get high gains in the non-selective channels. As the bandwidth of system gets wider, it becomes more severe frequency selective fading environments so that the reliability of data becomes lower and error flow is occurred. FE method, this paper proposed, uses the relation between sub-carriers of OFDM in frequency selective fading channels so FE method gets some gains by adapting the power value at a target frequency to the mean value of channel estimated values of adjacent sub-carriers. Because FE uses only preamble unlike DDCE using data, it is independent of data rate related to the reliability of data and the number of multipath. Consequently, FE can obtain considerable gains in the wideband systems where the errorflow of DDCE is occurred, and FE is applicable to frequency selective fading environments.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.4
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• pp.784-799
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• 2013

This paper presents an adaptive rate control scheme for streaming-based content sharing service. This scheme delivers multimedia contents from a user device to another device or seamlessly redirects streaming service across heterogeneous user devices. In the proposed scheme, a streaming server adjusts video quality level according to the network and client status. Our scheme is different from other rate control schemes, because the video quality at the server is decided not only based on the available bandwidth, but also based on the device characteristics and bandwidth requirement at the access network. We also propose a bandwidth estimation method to achieve more equitable bandwidth allocations among streaming flows competing for the same narrow link with different Round Trip Times (RTTs). Through the simulation, we prove that our scheme improves the network stability and the quality of streaming service by appropriately adjusting the quality of the video stream. The simulation results also demonstrate the ability of the proposed scheme in ensuring RTT-fairness while remaining throughput efficient.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.431-433
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• 2018

This paper proposes the system that offer super-wideband speech which is made by artificial bandwidth extension technique using wideband speech signal in time-domain. wideband excitation signal and line spectrum pair(LSP) are extracted based on source-filter model in time-domain. Two parameters are extended by each bandwidth extension algorithms, and then, super-wideband speech parameters are estimated. and synthesized. Subjective test shows super-wideband speech is better speech quality than wideband speech signal.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11A
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• pp.898-903
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• 2009

In this paper, the required frequency bandwidth for short range communications and mobile communication networks is analyzed for the matured Personal Environment Service, which establishes intelligent personal living environment with connecting the mobile phone and living appliances to WPAN, mobile communication networks, and Internet. In spite of rough estimation of the service needs, this paper shows the calculation method of required frequency bandwidth for the service and the considerations for the Ubiquitous era in advance.