• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.627-633
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• 2006

In spite of many advantages of Meteor Burst Communications(MBC) on its transmission channel, the fact that its duty rate is less than 10 percents is a considerable deficiency of MBC. To overcome with this deficiency without paying large cost, we use a direct sequence(DS) simple reception system. This method doesn't need to add the components for acquisition or tracking the signal so that it keeps the cost efficiency of the MBC. But it has a disadvantage that its duty rate shows a large decline by noise. For this problem we adopt the proposed system applying a transversal filter circuit. The improvement by this method is more significant when the received signal is weak Simulation results show as t1 is 100ms, then the burst length would be increased by 35% when the initial value of the received signal power increases by 3 dB, t2 is 135ms. If the power increases by 6dB the burst length would be 170ms thus increased by 70%, which shows a great enhancement. Suppose now that t1 is 50ms and the power is increased by 3dB, then t2 would be increased by 70% to 85ms, and increasing the power by 6dB it would be increased by 130% to 115ms.

• Korean Journal of Remote Sensing
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• v.38 no.3
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• pp.251-263
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• 2022

This paper presents an idea of ScanSAR image formation. For image formation of ScanSAR that utilizes the burst mode for raw signal acquisition, most conventional single burst methods essentially require a step of azimuth stitching which contributes to radiometric and phase distortions to some extent. Time-domain cross correlation could replace SPECAN which is most popularly used for ScanSAR processing. The core idea of the proposed method is that it is possible to relieve the necessity of azimuth stitching by an extension of Doppler bandwidth of the reference function to the burst cycle period. Performance of the proposed method was evaluated by applying it to the raw signals acquired by a spaceborne SAR system, and results satisfied all image quality requirements including 3 dB width, peak-to-sidelobe ratio (PSLR), compression ratio,speckle noise, etc. Image quality of ScanSAR is inferior to that of Stripmap in all aspects. However, it is also possible to improve the quality of ScanSAR image competitive to that of Stripmap if focused on a certain parameter while reduced qualities of other parameters. Thus, it is necessary for a ScanSAR processor to offer a great degree of flexibility complying with different requirements for different applications and techniques.

• The KIPS Transactions:PartC
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• v.11C no.5
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• pp.671-676
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• 2004

In this paper, we propose ultra-fast multimedia optical subscriber access network using optical frequency domain CDMA method in order to access the multimedia with multiple data rates. We numerically analyze the effects of spectral power distortion in the light source for the optical CDMA system modified PN codes and FBG(Fiber Bragg Grating)s. In the proposed multiple-rate multimedia access optical networks, the performances such as BER(Bit Error Rate) are the same for all data regardless of data rates in the case of the same number of simultaneous ONU. In the proposed ultra-fast multimedia optical subscriber access network, the performances for all data are much more improved than those in the conventional system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.13 no.1
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• pp.94-105
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• 1988

In this paper, we deal with to survey a narrow band ISDN transmission capability through the local subscriber line in Korea. First, we disscuss international activity trends of technical references required for a narrow band ISDN services using existing pair cables. Second, we have measured transmission characteristics to send digital signals at 144kbps ratio through the local subscriber line With this result, we have found that 3.6% of measured lines are not availlable for a narow band ISDN channel, obtained a conclusion that the input level of U-transceiver should be more than -31dBm so as to assure the sufficient digital transmission quality. We also know that majority noise cased by transmission error are due to impulsive noise and near end crosstalk. Fianlly. as a result of the BER measruement, it is observed that, within 2.5km, more than 70% of measured cables are satisfied with the reference quality.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 2002.06a
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• pp.76-79
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• 2002

Ghost cancelers need to accurately estimate the distortions suffered by transmitted signals on their way to receivers by capturing ghost canceling reference signals in the vertical blanking interval. As ghosts become much severer, sync separation tends to malfunction, making it impossible to acquire measurement data for channel estimation. This paper presents a robust method of acquiring ghost data using their correlation properties, and evaluates its performance through computer simulation. The reference signals are inserted in such a manner that the polarity alternates from one frame to another to remove color bursts and sync signals, and to increase the signal-to-noise ratio as well. As a result, however, they are prone to timing jitters. So a simple yet effective method is proposed that can correct for even fractional time delays. The timing errors are found to be less than about 4% of the sample spacing.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.11A
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• pp.1073-1080
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• 2005

In spite of many advantages of Meteor Burst Communications(MBC) on its transmission channel, the fact that its duty rate is less than 10 percents is a considerable deficiency of MBC. To overcome with this deficiency without paying large cost, we use a direct sequence(DS) simple reception system. This method doesn't need to add the components for acquisition or tracking the signal so that it keeps the cost efficiency of the MBC. But it has a disadvantage that its duty rate shows a large decline by noise. For this problem, we adopt the proposed system applying a positive feedback circuit. The improvement by this method is more significant when the received signal is weak. Simulation results show as tl is l00ms, then the burst length would be increased by $35\%$ when the initial value of the received signal power increases by 3 dB, t2 is 135ms. If the power increases by 6dB the burst length would be 170ms thus increased by $70\%$, which shows a great enhancement. Suppose now that tl is 50ms and the power is increased by 3dB, then t2 would be increased by $70\%$ to 85ms, and increasing the power by 6dB it would be increased by $130\%$ to 115ms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12B
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• pp.1728-1735
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• 2011

In this paper, satellite data link waveform is proposed which is based on the waveform of Link-16 but LDPC code is studied instead of CCSK code in order to be optimized to satellite nonlinear channel environment and transmission characteristics. And the DSM (Demux, Selective CH switch, and Mux) transponder structure is suggested which can remove all of the jamming signal out of the transmission signal band and convert uplink hopping frequency to desired ones of downlink. The results of BER and anti-jamming performance analysis shows that the required Eb/No and processing gain in the worst case partial band jammer of the proposed waveform are 2.5dB and 52dB respectively and the anti-jamming capacity improvement of DSM transponder is maximum 2dB.