• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.428-431
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• 2004

A multi-stage hierarchical clustering technique, which is an unsupervised technique, has been proposed in this paper for classifying the hyperspectral data .. The multistage algorithm consists of two stages. The 'local' segmentor of the first stage performs region-growing segmentation by employing the hierarchical clustering procedure with the restriction that pixels in a cluster must be spatially contiguous. The 'global' segmentor of the second stage, which has not spatial constraints for merging, clusters the segments resulting from the previous stage, using a context-free similarity measure. This study applied the multistage hierarchical clustering method to the data generated by band reduction, band selection and data compression. The classification results were compared with them using full bands.

• Journal of Broadcast Engineering
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• v.16 no.5
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• pp.714-721
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• 2011

MPEG audio uses the masking effect, high frequency component synthesis based on spectral band replication, and channel expansion based on parametric stereo for efficient compression of audio signals. In this paper, we present an overview of the state-of-the-art channel expansion technology in MPEG audio. We also present technical overviews and application examples to broadcasting services for HE-AAC v.2, MPEG Surround, spatial audio object coding (SAOC), and unified speech and audio coding (USAC) which are MPEG audio codecs based on the channel expansion technology.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.291-294
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• 1999

This paper presents a GaAs MESMET self oscillating mixer for high efficiency L-band frequency conversion with small chip area consumption. Main circuit topology is consist of cascoded two FET with resonating part. The circuit is designed as unstably nonlinear for limited frequency band. FET with drain shorted to source is used for frequency tuning element. Linear conversion gain of -18.83 ㏈ is achieved with 9mA and 4V consumption. Input 1㏈ compression point is more than 11㏈m. The chip area is 1.4$\times$1.4 mm.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.346-349
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• 2003

A SiGe HBT MMIC double balaced up-converter has been designed and fabricated for C-band WLAN applications. The up-converter is based on the Gilbert cell mixer with an active baluns for differential inputs of LO and IF signals. The designed up-converter exhibits a conversion gain 12.5dB for a -10 dBm LO power. It also exhibits LO-RF isolation of 19.3dBc, and IF-RF isolation of 23.3 dBc at a 1-dB compression point of -14.2dBm

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.12
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• pp.27-33
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• 1999

A wavelet based multiresolution watermarking method using the human visual system (HVS) is proposed, in which a different number of watermarks, in proportion to the energy contained in each band, are embedded into each band. Experiments with various test images show that the proposed three-level wavelet based method is robust to various attacks such as joint photographic experts group (JPEG) compression, smoothing, cropping, collusion, multiple watermarking, and so on.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2001.11a
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• pp.464-468
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• 2001

In this paper, we propose a robust watermarking technique that accepts time scaling, pitch shift, add noise and a lot of lossy compression such as MP3, AAC, WMA. The technique is developed based on digital filtering. Being designed according to critical band of HAS (human auditory system), the digital filters nearly affect audio quality. Furthermore, before implementing digital filtering, wavelet transform decomposes the audio signal into several signals that is composed of specific frequencies. Designed digital filters scan the decomposed signal. The designed digital filter, band-stop filter, distorts and eliminates specific frequencies of audio signals. Watermarking detection can be accomplished by FFT (Fast Fourier Transform). Firstly, segments of audio signal are transformed by FFT. Then, the obtained amplitude spectrum by FFT is summed repeatedly. Finally the watermark detector can find filters used to watermark encoding based on eliminating frequencies. The suggested technique can embed 4bits/s in a robust manner.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.967-968
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• 2006

This paper proposes a novel system to send images in a narrow band network and to measure water level. In order to send images in narrow band network, we use JPEG compression technique based on the difference image. The difference image is obtained by subtracting the current image from the predefined reference image. The water level is measured to make use of the camera calibration and the edge information of the received image.

• Geomechanics and Engineering
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• v.15 no.5
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• pp.1047-1059
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• 2018

This paper focuses on the cracking and fragmentation process in rock materials containing a pair of non-parallel flaws, which are through the specimen thickness, under vertical compression. Several numerical experiments are conducted with varying flaw arrangements that affect the initiation and tensile wing cracks, shear crack growth, and crack coalescing behaviors. To obtain realistic numerical results, a parallelized peridynamics formulation coupled with a finite element method, which is able to capture arbitrarily occurring cracks, is employed. From previous studies, crack initiation and propagation of tensile wing cracks, horsetail cracks, and anti-wing cracks are well understood along with the coalescence between two parallel flaws. In this study, the coalescence behaviors, their fragmentation sequences, and the role of an x-shaped shear band in rock material containing two non-parallel flaws are discussed in detail on the basis of simulation results strongly correlated with previous experimental results. Firstly, crack initiation and propagation of tensile wing cracks and shear cracks between non-parallel flaws are investigated in time-history and then sequential coalescing behavior is analyzed. Secondly, under the effect of varying inclination angles of two non-parallel flaws and overlapping ratios between a pair of non-parallel flaws, the cracking patterns including crack coalescence, fragmentation, and x-shaped shear band are investigated. These numerical results, which are in good agreement with reported physical test results, are expected to provide insightful information of the fracture mechanism of rock with non-parallel flaws.

• The Journal of the Acoustical Society of Korea
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• v.16 no.6
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• pp.110-114
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• 1997

When applying the nonuniform sampling to noisy speech signal, the required data rate increases to be comparable to or more than that by uniform sampling such as PCM. To solve this problem, we have proposed the waveform coding method, multiband nonuniform waveform coding(MNWC), applying the nonuniform sampling to band-separated speech signal[7]. However, the speech quality is deteriorated when it is compared to the uniform sampling method, since the high band is simply modeled as a Gaussian noise with average level. In this paper, as a good method to overcome this drawback, the high band is modeled as one of 16 codewords having different center frequencies. By doing this, with maintaining high speech quality as MOS score of average 3.16, the proposed method achieves 1.5 times higher compression ratio than that of the conventional nonuniform sampling method(CNSM).

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.8
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• pp.970-974
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• 2007

A mixer is a key component in the wireless communication systems. In this paper, we design a mixer which is used in a frequency modulated continuous wave(FMCW) radar system. The frequency sweep range of the radar is from 10 GHz to 11 GHz. The transmitted and received signals of the FMCW radar are applied to LO and RF ports of the mixer, respectively, but the frequency difference between the two signals, which is called "a beat frequency" is under a few KHz and depending on the distance to target. Thus the isolation between the LO and RF ports is very important factor to design this mixer. In this paper we propose a single balanced resistive mixer using GaAs MESFET for this application. We first design a single-ended type resistive mixer using a simulation tool, then design a balanced type to increase the LO-to-RF isolation of the mixer. We fabricated the mixer on the substrate of dielectric constant 10 and thickness 0.635 mm. The measured results show that the isolation and conversion loss of the mixer over the frequency band is 20dB and 10.5dB, respectively. The LO input power for operating the proposed mixer is +3dBm, which is lower than a general conventional mixer's LO power. The 1 dB compression point is 6dBm.