• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.10
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• pp.4561-4568
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• 2011

In this paper, carrier comparison PWM method for voltage control of Vienna rectifier is discussed. In general, in industrial and communications applications, the two-level rectifier is used. However, this two-level rectifier has the limit of high THD and low efficiency. So, the studies of three-level rectifier has been carried out so far, and the Vienna rectifier circuit is the representative. The space vector pulse width modulation(SVPWM) method is generally used for Vienna rectifier, in which voltage vectors and duration time are calculated from the voltage reference. However, this method require very sophisticated and complex calculations, so realizing this method by software is very difficult. To overcome this disadvantage, simple carrier comparison PWM method for Vienna rectifier is proposed which is modified from the carrier comparison method for 3 level inverter. Furthermore, to verify the usefulness of the Vienna rectifier carrier comparison PWM the simulation and experiment are carried out.

• Journal of the Korean Society of Radiology
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• v.2 no.4
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• pp.33-40
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• 2008

Images acquired by a digital X-ray imaging system are inherently degraded due to system degradation process and additive noise sources. The system degradation in image quality is typically described as the system response function characterized by the modulation transfer function (MTF) and the noise term described as the noise power spectrum (NPS). In this case, we can restore the blur image as close as possible to the original image by using modified filtering designed for digital imaging system, as we know more precisely about the MTF and the NPS. In this paper, by performing simulation, we tried to restore blurred images taken from a digital X-ray imaging system based upon conventional filtering techniques such as a direct-inverse filtering, limited-inverse filtering, or a Wiener filtering, and evaluated the characteristics of the image restoration.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.7
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• pp.1405-1412
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• 2015

Recently, Due to the rapid growth of broadcasting communication and video coding technologies, the demands for immersive media contents based on 3D stereoscopic video will increase steadily. And the demands must ultimately provide the contents for users which are in wireless channel such as vehicle, train, and ship. Thus, in this paper, we transmit the 3D stereoscopic video over the maritime Rician channel that direct wave is more dominant than reflective wave. Besides, we present unequel error protection (UEP) by applying hierarchical 4/16-QAM to V+D(Video plus Depth) format which can represent 3D stereoscopic video. We expect our system to provide seamless broadcasting service for users with poor reception condition.

• Journal of Navigation and Port Research
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• v.33 no.5
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• pp.303-308
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• 2009

Recently, unmanned systems have been studied and developed in various areas including aircrafts, automobiles and vessels. In addition, many researches about unmanned systems in Korea have been studying actively with the advancement of IT However, it is not satisfied with the result of the researches and developments. Bemuse of the reason we've here tried to make a very small USV which is a barge type. We applied the Great circle navigation calculation based on GPS to the autonomous navigation algorithm and used the LabVIEW 8.2 developed by NI corp. for programming The engine and rudder were controlled by pulse width modulation method. The engine system was composed of the DC motor and ESC(Electronic Speed Controller). It was also applied by the direct cooling system using DC motor pump. A very small USV was designed and made by ourself and it was verified the effectiveness of autonomous navigation algorithm through the tests at the sea.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9C
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• pp.855-862
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• 2009

The path key establishment phase in the wireless sensor network is vulnerable to Byzantine attack. Huang and Hedhi proposed a Byzantine resilient multi-key establishment scheme using a systematic RS code, which has shortcomings of exposing a part of message symbols and inefficient transmission. In this paper, we propose a new Byzantine resilient multi-path key establishment scheme in which direct message symbols are not exposed to an adversary and are more efficiently transmitted the RS-encoded symbols to the destination node. In the Proposed scheme, a non-systematic RS code is used to transmit a generated indirect secret key and each encoded symbol is relayed through available paths between two sensor nodes. If enough symbols are collected at the destination node, it is possible to reconstruct the secret message through RS decoding.

• Korean Journal of Optics and Photonics
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• v.11 no.1
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• pp.58-64
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• 2000

Assuming that the performance of holographic storage media is ideal, we estimate the area storage density of disk-type holographic memories, when the method of either angle multiplexing, or rotational multiplexing, or both are used. The area storage density is strongly dependent on the f numbers (ratio of focal length to diameter) of both the Fourier transform lens in the signal arm, denoted by $F/#_2$, and the angle range over which the reference beam is incident (or, the equivalent f number corresponding to the angle range denoted by $F/#_1$). The area storage density is largely independent of the pixel pitch of the spatial light modulator when the Fourier plane holograms are recorded, while it is sensitive to the pixel pitch when the image plane holograms are recorded. In general, to obtain high area storage density, the Fourier or at least near Fourier plane holograms rather than the image plane holograms should be recorded. In addition, when the thickness of the recording materials are less than approximately $500\mu\extrm{m}$, rotational multiplexing gives higher area storage densities than angle multiplexing does. To increase the storage density further, however, it is desirable to use both of the two multiplexing methods in combination.nation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.9
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• pp.939-950
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• 1992

The performance of common spreading code scheme employing multiple-capture receiver is compared to that of transmitter-oriented (T/O) code division multiple access (CDMA) scheme in view of the possibility of collision-free transmissions and the effect of secondary multiple-access interference. For performance comparisons, secondary multiple-access interference is characterized for the common code scheme and the T/O CDMA scheme that assures perfectly collision-free transmissions. Throughput performance is then evaluated for these two schemes with direct-sequence spread-spectrum/differential-phase-shift-keying (DS-SS/DPSK) data modulation and forward-error-control coding (BCH codes) in the presence of an additive white Gaussian noise (AWGN). It is shown that when the number of radios is relatively large, the maximum normalized throughput is greater for the common code scheme than for the T/O CDMA scheme at a moderate signal-to-noise ration(SNR).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.3C
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• pp.314-319
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• 2010

The chirp spread spectrum (CSS) technique that spreads the data signal over a wider frequency band via chirp signal for transmission has attracted much attention in the field of wireless communications due to capability to resist multipath fading signals. However, there has been little mathematical analysis for the performance of CSS-based communication systems in the multipath fading environments. In this paper, we study the influence of the multipath channel on the direct modulation (DM) scheme with M-ary phase shift keying (MPSK). When a chirp signal is transmitted on the Rayleigh fading channel and affected by additive white Gaussian noise (AWGN), we derive the theoretical performance. From numerical results, it is confirmed that the analytic symbol error rate (SER) agrees closely with the empirical SER.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.4 no.4
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• pp.286-294
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• 2011

Cable modems typically are implemented by a forward error correction(FEC) scheme. The ITU-T Recommendation J-38 Annex B specifies using 64- and 256- quadrature amplitude modulation (QAM) and extended RS coding scheme. In implementing the cable modem, there are some problems to fabricate and fitting on FPGA chip. First, many clocks are needed in implementing cable modem because of different code rate and different modulation types. To reduce the number of clocks, we use the two memories, which are different clock speed for reading and writing data. Second, this system lost the bit-synchronization and frame-synchronization in decoder, the system recognize that all data is error. This paper solves the problems by using simple 5-stage registers and unique sync-word. Based on solutions for about problems, the cable modem is fabricated on FPGA chip name as Vertex II pro xc2vp30-5 by Xilinx, and we confirmed the effectiveness of the results.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.161-166
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• 1999

The global trends of mobile communication system is moving toward digitizing, high-speed and large-capacity. Also, to utilize the limited frequency-resource efficiently, spread spectrum system is a mainstream. In this study we are concerning with the fast frequency-hopping system. Instead of the PLL with many problems such as phase-noise, we used the DDS is popular in these days minimizes the disadvantage of PLL. In the case the FFH system is designed using the PLL, it is difficult to be satisfied of the design conditions such as RF badwidth and the settling time of PLL, and it has limitation because of complex circuit by using the balanced modulator. In this study, we evaluated the performance in order to design the FFH system using the DDS. The system that has the improvement of error rate, 1Mhps hopping rate and 5MHz RF bandwidth is designed and evaluated.