• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.6
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• pp.42-48
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• 2010

Joint Tactical Information Distribution System (JTIDS) uses cyclic code shift keying (CCSK) for baseband symbol modulation, in which 5-bit information is mapped to one of thirty two 32-chip sequences. It is a kind of direct sequence based spread spectrum communication. In this paper, the performance of non-coherent detection of CCSK using non-orthogonal 32-chip sequence is evaluated. And a 32-chip sequence with better performance is also proposed and compared with the conventional one.

• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.5
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• pp.465-470
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• 2010

This paper proposes an adaptive video watermarking algorithm according to bit detection rate of watermark in MPEG2 system. The watermark strength is adaptively applied as BER(bit error rate) of watermark extracted from decoded frame for motion compensation. Watermark insertion uses a frequency spread spectrum method. A realtime watermark extraction is done directly in the DCT domain during MPEG decoding. The experimental simulations show that PSNR(peak signal to noise ratio) results 31.5dB for a fixed watermark strength and 33.dB for an adaptive watermark strength. Also average BER is 0.126 and less than 0.2 avaliable value.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.1
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• pp.61-72
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• 1997

The implementation of base station transceiver for Wideband CDMA(Code Division Multiple Access) PCS(Personal Communication Service) system using spread spectrum CDMA technology is presented in this paper. The receiver that requires wide dynamic range and high sensitivity and the transmitter that has good spurious emission supression were designed and implemented with 5 MHz RF channel bandwidth. This paper shows the some factors that should be considered and simulated using the RF simulation S/W with commercial and customized components. The implemented transceiver based on the simulation gave good results that satisfied the functional specifications of the transceiver.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.1
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• pp.115-123
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• 2018

In this paper, we consider the applicability of time-hopping(TH) systems for anti-jamming(AJ) communication. We first briefly summarize fundamentals of TH systems and several common jamming scenarios that have been considered in the literature. We then analyze the AJ performance of TH systems under those common jamming environments. From our simulation results, we reveal that among narrow band, partial band, broadband, and sweep jamming, partial band and sweep jamming are the best ones from jammer perspective. For the partial band jamming case, we show that the most effective bandwidth ratio and location are 50 % and 2.5-3.5 Ghz, respectively. For the sweep jamming case, we illustrate that the AJ performance of the TH system is enhanced when the sweep duration approaches to the bit duration. In addition, we pointed out that the most efficient jamming bandwidth ratio is 1/2. Finally, our results show that the TH-BPSK system greatly outperforms the TH-PPM counterpart.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.7A
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• pp.635-640
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• 2002

We investigate optimal and suboptimal decision rules for parallel code acquisition in chip asynchronous direct-sequence spread-spectrum systems. The conventional decision rule for parallel acquisition is to choose the largest correlator output of a receiver. However, such a scheme is optimum only for chip synchronous models. In this paper, an optimal decision rule is derived based on the maximum-likehood criterion for chip asynchronous models. A simpler suboptimal decision rule is also discussed. The performance of the optimum and suboptimum decision rules is compared to that of the conventional decision rule. Numerical results show that, for chip asynchronous models, both the optimal and suboptimal decision rules outperform the conventional decision rule.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.10A
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• pp.1159-1166
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• 2004

This paper follows up the previous work on the linearly constrained, modified minimum mean-squared error(MMSE) detection for direct-sequence code-division multiple-access DS-CDMA) systems in fading channels. We find a condition to avoid the breakdown of joint modified MMSE detection and pilot symbol-aided channel estimation (PSACE). The linearly constrained, modified MMSE solution is theoretically shown to be robust against time variations in Rayleigh fading channels. This fact is consistent with the simulation results. We also show that under some conditions the linearly constrained, modified MMSE detection maximizes the output signal-to-interference-plus-noise ratio.(SINR)

• The KIPS Transactions:PartB
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• v.14B no.5
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• pp.337-342
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• 2007

Multi-level has advantage to express image in all levels with different images. This paper proposes digital watermarking built-in technique to transform color image to YCbCr color space to guarantee robustness and imperceptibility of the watermark in the various expression of color images, and to hide multi-level data which shows spread spectrum from low resolution to whole resolution for the Y-signal of multi-level. In color signal, Y-signal and low resolution built-in watermark has risk to be visible, but it can guarantee the robustness of watermark in various colors and transformed images. As a result of the experiment, wavelet compression image with built-in watermark showed robustness and imperceptibility of watermark.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.12 no.2
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• pp.168-175
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• 1987

In this paper, a FFH-SS hybrid communication method using digital frequency synthesizer is proposed. This can simultaneously share the same frequency band with conventional band limited communication method without interference. In the experiment the selective hopping pattern is attained by some conbination of serial to parallel conversion of maximal code from pseudo random noise generater, and it is observed that the selective hopping band transition can be more easily achieved when the hop interval is nonuniform than it is uniform. Digital frequency synthesizer is now reported to have very poor spurious suppression ability below 50~60dB, the reason of this is observed from the experimental result, and the way of how to solve this problem is presneted.

• Journal of the Korea Society of Computer and Information
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• v.3 no.4
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• pp.35-43
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• 1998

This study has been experimented the characteristics of synchronous oscillator for clock recovery of Direct Sequence/Spread Spectrum(DS/SS) communication. When external wave is not provided, The Synchronous Oscillator(SO) oscillates at its natural frequency. As soon as external signal is applied, the SO starts tracking the external frequency which can be sinusoidal, pulsed or some other waveform. Thus, the output is synchronized with the range of wide tracking bandwidth to the external frequency Specifically, the SO also posses frequency division and multiplication capability. All of these indicate that the SO can overcome difficulties to get synchronization in coherent digital communication systems. We make a practical application of DS/SS communication with study on the synchronous properties of SO. As the result, we have a good performance.

• Journal of Marine Bioscience and Biotechnology
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• v.8 no.1
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• pp.10-17
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• 2016

A wide-spread contamination of persistent organic pollutants (POPs) such as dioxins, PCBs, PBDEs in the aquatic ecosystem has generated a great concern over the potential risk for these substances to impact marine biotas and food web. Since a major exposure route of these substances to the humans is through the consumption of food including fish and marine byproducts, the consumption of contaminated products has been a great public health concern. Exposure to POPs has been associated with a wide spectrum of adverse effects including reproductive, developmental, immunologic, carcinogenic, and neurotoxic effects. This review covers the background information of key POPs substances and the recent development of toxicity studies including the mode of action. Because neurotoxic effects of some POPs have been observed in humans at low concentrations, polychlorinated biphenyl (PCB), a representative chemical of POPs, is focused to discuss the possible mode(s) of action for the neurotoxic effects. This review provides the updates of toxicity studies on POPs and paves ways to discuss a possible implication of contaminated marine biota over the human health among the marine biotechnology researchers.