• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.7
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• pp.499-507
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• 2003

This paper presents a method for active noise control (ANC) in a duct by using a ring-tyPe smart foam. The ring-type smart foam consists of an elastic porous material of lining shape and a PVDF film embedded In the material. The PVDF element acts as a secondary sound source to reduce the noise. Active noise control using a ring-type smart foam is only effective locally because of the way to excite radially. To enlarge the quiet zone, the duct Is lined with additional acoustic foam between the smart foam and the error microphone. When cancellation path ks optimized by the LMS/RLS algorithm, the computation power is reduced while control performance Is maintained. The filtered-x LMS algorithm is used to minimize the error signal.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.525-529
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• 2002

ANC technic can overcome the limited performance of passive noise control at the low frequency range. But it has the local quiet control region in general. In this paper, it is discussed that the global noise control in a circular duct using a ring type smart foam and a porous material. LMS algorithm and RLS algorithm are used to find optimal orders of cancellation path. Experiments are performed to compare the efficiency of RLS algorithm with that of LMS algorithm.

• Journal of KSNVE
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• v.9 no.3
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• pp.600-606
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• 1999

A reactive type acoustic filter is developed based on the phase cancellation effect which is occurring in the plane wave propagation through the two paths where the cross sectional areas are reversely changing. The theory is experimentally validated by the use of a cylindrical duct and an inserted hollowed cone of which vertex part is eliminated. Noise attenuation and the filtered frequency are dependent on the area variation and the effective length of the filter. Experimental comparison shows that the filtered frequencies of 1st and 2nd mode are lower than the analytical prediction due to the mass loading effects, and the 3rd mode is in good agreement. The proposed filter can be applied as an in-duct noise filter for improving the sound quality in a narrow space for various industrial applications.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.1
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• pp.202-211
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• 2001

This paper deals with an analysis of multipath which affect a transmission performance in underwater acoustic channel. Underwater acoustic channel with multipath structure is introduced to mathematical modelling for a basin environment. In this paper, SMR(Signal to Multipath Ratio) which is defined as a parameter of multipath's effect is presented as a mathematical equation, and the equation of SMR is simulated by MATLAB program. Furthermore, this paper is also dealt with an implementation of modulation and demodulation system for acoustic transmission. Acoustic Transmission is limited by frequency bandwidth, so $\pi/4 QPSK$(Quadrature Phase Shift Keying) methods which is very useful at frequency ]imitation and FM(Frequency Modulation) are used at acoustic communication system. This implemented hybrid modulation/demodulation system is used as an analog board of image transmission system. In this system, adaptive equalization for reducing the multipath effect and baseline JPEG used for an image compressing are also stated.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.05a
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• pp.419-425
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• 2000

This paper deals with an analysis of multipath which affect a transmission performance in underwater acoustic channel. Underwater acoustic channel with multipath structure is introduced to mathematical modelling for a basin environment. In this paper, SMR(Signal to Multipath Ratio) which is defined as a parameter of multipath's effect is presented as a mathematical equation, and the equation of SMR is simulated by MATLAB program. Furthermore, this paper is also dealt with an implementation of modulation and demodulation system for acoustic transmission Acoustic Transmission is limited by frequency bandwidth so $\pi$/4 Quadrature Phase Shift Keying) methods which is very useful at frequency limitation and FM(Frequency Modulation) are used at acoustic communication system. This implemented hybrid modulation/demodulation system is used as an analog board of image transmission system

• Korean Journal of Cognitive Science
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• v.8 no.4
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• pp.11-18
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• 1997

야간 시각은 민감도를 극대화하고 주간 시각은 세감도를 극대화한다. 민감도와 세감도는 시각 기능의 두 목표이지만 상쇄적인 작용때문에 균형적인 선택이 요구된다. 민감도와 세감도를 결정하는 중요한 요인으로는 광학적인 요인과 신경학적인 요인이 있다. 망막의 지역적 분화는 바로 이러한 민감도-세감도 문제에서 기인하는데 망막의 2차원적인 제약이 시각신경계의 병행적인 경로와 이에 기초한 적응적 진화를 통해서 어느 정도 해소되는 듯이 보인다. 이 글은 야행-주행 습성을 동시에 갖추어 민감도와 세감도의 균형 문제가 각별히 부각되는 고양이의 초기 시각신경계에서 민감도와 세감도의 균형을 최적화하는 신경 기전을 소개한 것이다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.25-30
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• 2017

Millimeter wave (mmWave) bands are expected to improve date rate of 5G systems due to the wide available bandwidth. While severe path loss in those bands has impeded the utilization, short wavelength enables a large number of antennas packed in a compact form, which can mitigate the path loss. However, estimating the channel with a conventional scheme requires a huge training overhead, hence an efficient estimation scheme operating with a small overhead needs to be developed. The sparsity of mmWave channels caused by the limited scatterers can be exploited to reduce the overhead by utilizing compressed sensing. In this paper, we introduce compressed sensing techniques for mmWave channel estimation. First, we formulate wideband channel estimation into a sparse recovery problem. We also analyze the characteristics of random measurement matrix constructed using quantized phase shifters in terms of mutual incoherence.

• Journal of Distribution Research
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• v.4 no.2
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• pp.1-20
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• 1999

This study aims to provide distributors with several implications on the channel strategy by testing factors which influence on the offsetting investment. Medium-sized distributor facing a relatively inferior power can cause profit vulnerability from large manufacurer's opportunistic behaviors. At the same time, we tested the relationship commitment to the relation with manufacturer as another alternative strategy taken by medium-sized distributer. For this research, samples from dealers in oil-petroleum refinery industry were selected and the data was collected using mail survey. The data was analyzed utilizing validity test, reliability test, factor analysis, correlation analysis and LISREL. The major analyzed results are as follows: First, the offsetting investment of preventing loss from manufacturer's opportunism didn't affect medium-sized distributor's sales empirically. Second, the hypothesis that the more the medium-sized distributor's transaction specific assets which they invest in the transactional relationship with manufacturer, the more the safeguard against the expected opportunism of manufacturer was not supported by the results. Third, the more use of coercive power by the manufacturer, the more increase in the perception of expected opportunism of manufacturer by the medium-sized distributor, it make stimulates offsetting investment as safeguard by medium-sized distributor and it has negative effect on developing commitment. Finally, the large manufactures dealing with a medium-sized distributor firm which had a reputation of fairness didn't make offsetting investment as a response for distributor's opportunism.

• The Journal of the Acoustical Society of Korea
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• v.35 no.4
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• pp.295-302
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• 2016

Underwater acoustic communication channel is often defined as a multipath fading channel since the multipath arrivals from various paths interfere with each other and cause frequency dependent constructive or destructive interference in received signals. Therefore signal-to-noise ratio (SNR) of received signal fluctuates as a function of frequency. In addition, sea surface fluctuation induces frequency dependent time variant signal fading due to coherent component variation of surface bounce path. The frequency shift keying (FSK) system is known to be less sensitive and more robust under these interference and fading, and M-ary frequency shift keying (MFSK) system is adopted to increase a data rate. In this study, a bit error rate (BER) of 4 channels 4FSK system are examined in shallow sea multipath channel. Experimental results show that RS code reduces efficiently the BER of 4FSK system since frequency dependent time-varying fading is characterized to give burst errors. The BER of a different data rate or different source-to-receiver range depends on not only the channel coherent bandwidth but also frequency dependent multipath fading.

• Journal of Broadcast Engineering
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• v.5 no.2
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• pp.273-280
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• 2000

Channel characteristics between the outdoor transmitter far away from the building and receivers inside the building are explored theoretically using ray tracing technique. In this paper, 29 receivers are located on the single floor of the building to observe the variation of channel properties depending on receiver location. For each receiver, amplitudes and phases of ail the possible rays form the transmitter to the receiver are traced to obtain impulse response. Statistical results for rms delay spread and power delay profiles for representative receiver location are given.