• The Journal of the Acoustical Society of Korea
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• v.30 no.2
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• pp.86-91
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• 2011

In the underwater communications, the acoustic channel is in poor communication conditions, such as long propagation delay, narrow bandwidth, and high bit-error rate. For these bad acoustic channels, we propose an efficient automatic repeat request (ARQ) for multi-hop underwater network by using the concepts of concurrent bi-directional transmission, multiple sub-packets, and overhearing data packet instead of the acknowledgement signal. Our results show that the proposed ARQ significantly reduces the transmission latency especially in high BER compared with the existing Stop and Wait ARQ.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.103-106
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• 1999

Organic electroluminescent devices (OELDs) have received a great deal of attention due to their potential application as full-color displays. Europium complexes are known as excellent red light-emitting materials for OELDs since they show intense photoluminescence at around 612 nm with a narrow spectral bandwidth. In this study, a novel curopium complex, Eu(TTA)$_3$(TPPO) was synthcsizcd and its photoluminescent and electroluminescent characteristics were investigated with a device structure of ITO/TPD/Eu(TTA)3(TPPO)/A1q$_{3}$ Al, where sharp emission at the wavelength of 615 nm has been observed. Details on the electrical properties of these structures will be also discussed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.8
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• pp.1305-1312
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• 2000

This paper presents the design and implementation of the CPW end-coupled band-pass filter with the finitely backed conductor (FBC). To reduce the large insertion loss in CPW structure, the improvement in loss characteristic through the change of CPW structure is introduced. The CPW filters with narrow bandwidth are suggested and characterized for their microwave performance using the finitely backed conductor. This structure

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2389-2391
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• 2005

In this paper, a compact S type resonator is presented, where the proposed resonator is surface micromachined over transmission lines or other resonators, in order to obtain a wide range of possible electromagnetic couplings. The structure has been applied in two compact, bandstop and bandpass filters with moderate fractional bandwidths (FBW) of 20% and 25% respectively. The bandstop filter presented, was designed by the combination of two design methods in order to obtain the proposed fractional bandwidth, where traditionally, coupled resonator bandstop filters have been used for narrow stopbands. The bandpass filter illustrates the use of the proposed suspended resonator structure to obtain a wide range of electric type coupling coefficients, and external quality factors for the filter. This paper describes the design methodology, concepts and fabrication method proposed for the design of these filters.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.71-79
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• 2008

A helmholtz resonator has been widely used for the purpose of suppressing the low frequency noises propagated from various heat and fluid machineries. However, the conventional resonator has demerits that the effective absorption bandwidth is narrow and the absorption performance is not so outstanding in the only limited configurations of neck and cavity as well. In order to overcome these problems, in this paper, a resonator with perforated neck is proposed. The absorption performances of the resonator are measured by two-microphone method and estimated by transfer matrix method. The measured values of normal absorption coefficients agree well with the estimated values. By introducing the perforated plates at the neck of a resonator, it is shown that the absorption performance have been significantly improved.

• Journal of Korea Multimedia Society
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• v.17 no.5
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• pp.631-639
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• 2014

Recently, research on Media Access Control (MAC) techniques for underwater acoustic communication has been conducted actively. For successful acoustic communication in underwater conditions, development of environmentally adaptive MAC techniques, which is taking narrow bandwidth, distance, depth, noise level, salinity, multipath and etc into account, is an especially important work. In this paper, knowledge based system is introduced not only to obtain adaptive and optimal communication parameters but also increase network efficiency and availability by requesting change of MAC techniques based on decisions from knowledge-based system Smart Decision Block (SDB). Computer simulations were also conducted to verify the performance of the proposed system in underwater conditions.

• The Journal of the Korea Contents Association
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• v.9 no.9
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• pp.41-50
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• 2009

A conventional middleware system is optimized for wired computing environments. The wireless mobile devices have several disadvantages of low-speed processors, small memory and narrow bandwidth of wireless network. To overcome those problem issues in wireless mobile environments, middleware and many middleware-related applications have to be changed of the small sized components. In this paper, we design a lightweight mobile middleware system called "LightMware" which is optimized for mobile environment and middleware applications

• Journal of the Semiconductor & Display Technology
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• v.17 no.3
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• pp.95-99
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• 2018

In this study, take a look at natural disasters and technical characteristics such as frequency, bandwidth, transmission power, and service coverage of mobile communication and terrestrial broadcasting are compared as a means to provide disaster warning service in case of natural disaster, which is increasing in recent years. In the event of a disaster, mobile communication systems that take high frequency bands, low power transmission and narrow coverage can be disabled, but terrestrial broadcasting, which uses VHF and UHF with good frequency characteristics and high transmission power and wide service coverage provides stable services. As result terrestrial broadcast is useful as emergency warning or information in case of disaster.

• Publications of The Korean Astronomical Society
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• v.38 no.2
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• pp.75-89
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• 2023

Technosignature, previously known as SETI(search for extraterrestrial intelligence), is the scientific evidence of past or present extraterrestrial civilizations. Since NRAO's Project Ozma was performed in 1960, most of the noticeable technosignature searches have been done by radio telescopes, hoping to find strong and narrow bandwidth signals that cannot be explained by known natural processes. Recently, the Breakthrough Listen project has opened a new opportunity for technosignature by utilizing both optical telescopes, radio telescopes, and next-generation radio telescope arrays. In this review, mainly based on NASA Technosignatures Workshop (2018), we review the current trends of technosignature surveys, as well as other possible methods for detecting technosignature. Also, we suggest what the Korean community could contribute the technosignature research, including the new SETI project with Korea VLBI Network (KVN).

• Proceedings of the Korean Society of Computer Information Conference
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• 2020.07a
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• pp.139-142
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• 2020

NB-IoT(Narrow Band Internet of Things) is an emerging LPWAN(Low Power Wide Area Network) radio technology. NB-IoT has many advantages like low power, low cost, and high coverage. However low bandwidth and low sampling rates also lead to poor positioning accuracy. This paper proposed a solution to optimize positioning accuracy under the OTDOA(Observed Time Difference of Arrival) approach by utilizing MLR(Multiple Linear Regression) models. Through the MLR model to predict the influence degree of weather(temperature, humidity, light intensity and air pressure) on the arrival time of signal transmission to improve the measurement accuracy. The improvement of measurement accuracy can greatly improve IoT applications based on NB-IoT.