• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.8-12
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• 2007

In this paper, we proposed an frequency offset estimation scheme which can be used for packet based OFDM communication systems such as IEEE802.11a and IEEE802.11p physical layer. Proposed estimation scheme can adjust the gain allocation ratio between long training symbol and short training symbol while maintaining average power of overall training sequence so that we can obtain the reference parameters for MSE performance improvement. The preamble structure considered in this paper is based on the preamble specified in IEEE802.11a and IEEE802.11p standardization group. From the simulation results, it is shown that power ratio between long training symbol and short training symbol must vanes for achieving lower frequency offset estimation error as channel SNR condition is changed. Also it is known oat proposed scheme can achieve better performance than conventional one.

• The Journal of the Acoustical Society of Korea
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• v.24 no.5
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• pp.238-247
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• 2005

In this Paper. we Presents subband design techniques of a compensating filter and adaptive feedback canceller for the digital hearing aid. The sensorineural hearing loss has a hearing threshold that shows a nonlinear characteristic in frequency domain. and its compensation suffers from an echo that produced by an undesired time varying feedback path. Therefore. the digital hearing aid requires the compensator that can adjust gains nonlinearly in frequency bands and eliminate the echo rapidly In the Proposed digital hearing aid. the compensating filter is designed by the adaptive system identification method in subband structure, and the adaptive feedback canceller is designed by the subband affine projection algorithm. The designed compensation filter can control the nonlinear gain in each subband respectively, therefore precise compensation is possible. And the feedback canceller using the subband adaptive filter achieves fast convergence rate. The Performances of the Proposed method are verified by computer simulations as comparing with the behaviors of the previous trials.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.4
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• pp.83-92
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• 1999

본 논문에서는 Jue Chang 과 John R. Glover 가 1993년에 제안한 회귀적 적응 주기 신호 검출기[1]를 소개하고 이를 구현하기 위한 최적의 실시간 알고리즘을 제안하여 회귀적 주기 신호 검출기의 실용적인 응용 예를 제시하였다. 회귀적 적응 주기신호 검출기(FALE:Feedback Adaptive Line Enhancer)는 기존의 적응 주기 신호 검출기에 회귀 경로를 달아줌으로써, 필터 차수를 같게 했을 때 낮은 신호 대 잡음비 환경 하에서 더 높은 필터 이득과 더 낮은 추정 오차를 얻을 수 있다. 회귀 경로를 통해 들어오는 필터 출력 신호는 회귀 이득 상수 값에 따라 전체 시스템의 성능이 달라지므로 최적의 회귀 이득 상수를 찾아내는 것이 중요하며 이는 회귀 이득 상수를 변화시키며 최적의 결과값(최소 추정오차)을 유도하는 실험을 통해 얻을 수 있다. 한편, 이를 구현하는 문제에 있어서는 일잔 최적의 회귀 이득 상수 값이 정해지면 회귀 이득 상수가 초기 값으로부터 최적 값에 도달하는 변화율과 변화 유형이 시스템의 실시간 구현 및 성능에 중요한 영향을 미치게 된다. 본 논문에서는 실험을 통해 최적의 구현 알고리즘을 찾아냄으로써 Jue Chang 과 John R, Glover가 제시한 이론적인 수렴율과 수렴 성능을 유지하면서 실시간으로 동작하는 시스템을 구현하고 모의실험을 통한 성능분석 결과를 제시하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.1
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• pp.28-36
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• 2016

Theoretical model of a variable thrust solid rocket motor with a pintle nozzle was derived. For the chamber pressure control, classical model linearization and proportional-intergral controller was used. And then two types of gain scheduling controller were suggested to imporve controller performance for the non-linear propulsion model. Considering characteristics of systems, control gains were scheduled by chamber pressure or free volume. Step responses of each controllers were compared. As a result, the proper control algorithm about characteristics of variable thrust rocket motor was suggested.

• Journal of Korea Society of Industrial Information Systems
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• v.19 no.2
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• pp.37-43
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• 2014

In this paper, we present the effect of forward current gain on emitter area in NPN transistors are used widely in the almost linear integrated circuits and integrated injection logic. Relations between forward current gain and emitter area were conformed with the simulation with examined calculation and experiments. At the same emitter length, as junction depth is increased, common emitter current gain is decreased. Ratio of Emitter bottom area comparing to side area increases, the emitter current gain is increased. The theory and simulation results were fitted in with the experimental data very well.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4A
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• pp.363-369
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• 2004

We propose, for the first time to our knowledge, a novel gain-clamping method for EDFA in WDM add/drop networks by introducing a disturbance observer technique. The control input signal for gain-clamping is composed of a nominal control signal and an additional control signal of compensating the gain fluctuations caused by channel add/drops. Based on disturbance observer technique, we designed the additional control signal such that it has the compensating information of estimated disturbance resulted from channel add/drops. The circuit for generating additional control signal can easily be implemented by using simple electronic devices. We proved the superiority of the new technique over the previous ones by showing simulation results of minimized dips and spikes that appear in power profile of EDFA in the process of channel add/drops.

• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.427-435
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• 2016

Array Gain (AG) is a metric to measure the performance of an array of acoustic sensors. AG is affected by the configuration of array, frequency and array element spacing, and the directivity of the ambient noise. In this paper, an algorithm to calculate AG based on the spatial coherence is used, and the results are verified through sea-going experiment. The method using the spatial coherence can be used to consider the arbitrary shape of an array and directionality of ambient noise. In the sea-going experiment, the towed source was used to transmit the Continuous Wave (CW), and was received at the horizontal line array on the seabed. The ambient noise was measured between the source transmission. The experimental AG was calculated from the SNR (Signal to Noise Ratio) of single sensor and an array of sensors. Finally, the predicted AG is shown to agree with the experimental value of AG.

• The Journal of the Acoustical Society of Korea
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• v.34 no.3
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• pp.240-246
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• 2015

In this paper, speech enhancement using nonnegative matrix factorization with temporal continuity has been addressed. Speech and noise signals are modeled as Possion distributions, and basis vectors and gain vectors of NMF are modeled as Gamma distributions. Temporal continuity of the gain vector is known to be critical to the quality of enhanced speech signals. In this paper, temporal continiuty is implemented by adopting Gamma-Markov chain priors for noise gain vectors during the separation phase. Simulation results show that the Gamma-Markov chain models temporal continuity of noise signals and track changes in noise effectively.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2013.05a
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• pp.586-589
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• 2013

In this paper, the proposed scheme is STBC system combined with convolutional code to ensure the reliability of data transmission for a high rate wireless communication. In addition, this scheme uses a modified viterbi algorithm in order to get a high system gain when data is transmitted. Because we combine STBC and comvolutional code, the proposed scheme can get a diversity gain of STBC and coding gain of convolutional code at the same time. Unlike existing viterbi docoding algorithm using Hamming distance in order to calculate branch matrix, the modified viterbi algorithm uses Euclidean distance value between received symbol and reference symbol. To analyze the system proposed, it was simulated by changing the constraint length of the convolutional code and the number of transmit and receive antennas of STBC.

• Korean Journal of Optics and Photonics
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• v.4 no.3
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• pp.301-308
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• 1993

Phenomenological nonlinear gain saturation effect on the modulation characteristics in a multi-electrode DBR laser, when the lasing wavelength changes, continuously is analized theoretically. FM efficiency, 3 dB bandwidth, and resonance frequency decrease with increasing bias current to the passive section, except increasing the flat FM response. It is found that the nonlinear gain saturation effect severely affects the modulation characteristics such as FM/IM response, 3 dB bandwidth, resonance frequency and CPR, but hardly affects the behavior of continuous frequency tuning.