• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.6A
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• pp.379-385
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• 2003

In this paper, we propose a time constant control method for sieving local minimum problem of the multiuser detector using Hopfield neural network for synchronous multi-rate code division multiple access(CDMA) system in selective fading environments and its performance is compared with that of the parallel interference cancellation(PIC). We also assume that short scrambling codes of 256 chip length are used an uplink, suggest a simple correlation estimation algorithm and circuit complexity reduction method by using cyclostationarity property of short scrambling code.It is verified that multiuser detector using Hopfield neural network more efficiently cancels multiple access interference(MAI) and obtain better bit error rate and near-far resistant than conventional detector.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.12
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• pp.35-40
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• 2006

The combustion instability in a model dump combustor with an exhaust nozzle and the possibility of combustion control using a loudspeaker to these instabilities were studied. By changing inlet velocity, combustor length and equivalence ratio, dynamic pressure signals and flame structures were simultaneously taken. Because inlet velocity and combustor length affect the life time of vortex in the dump combustor, the results showed that as the combustor length increased and the inlet velocity decreased, the instability frequency decreased and the maximum power spectral density of the dynamic pressure generally decreased. Also, instability frequency and maximum power spectral density of the dynamic pressure increased with the increment of equivalence ratio. From the data of close-loop control, the optimum time-delay control using a loudspeaker was confirmed to be able to reduce the vortex shedding induced from the mixed acoustic-convective mode combustion instability.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.6
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• pp.28-38
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• 2019

To investigate the relation between flame structure and combustion dynamic characteristics in bi-swirl coaxial injectors for a liquid rocket engine, combustion experiments were performed using gaseous methane and gaseous oxygen. CH* radicals and pressure fluctuations were simultaneously measured by changing the injector geometries such as recess length/orifice diameter and the flow conditions such as equivalence ratio/oxidizer mass flow rate. As the injector geometries affected the velocities and mixing of the propellants, the change in flame structures was observed. From a result of the frequency analysis, it was confirmed that combustion dynamic characteristics varied according to the injector geometry/flow condition and combustion instabilities could occur under specific recess length/flow conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.5D
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• pp.663-669
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• 2011

In this study, the optimal length of left-turn lane in permissive left-turn signal system at the signalized intersection which has a left-turn bay is estimated. It is a simulation analysis using the queueing theory that estimate the length of left-turn lane. Traffic density conform to the standards of operating a permissive left-turn system of the Practical Manual Traffic Safety Facilities. And each of a left-turn arrival rate, a left-turn service rate, left-turn average queueing time, for green time average queueing vehicle, for red time average queueing vehicle and average queueing vehicle cycle is calculated. As a result of this study, we would learn how much the space should be secured at the signalized intersection which has a left-turn bay. The methodology using the queueing theory to work out the optimal length of waiting lane in the permissive left-turn signal system was presented.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.5
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• pp.892-901
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• 2001

Despite of many advantages over conventional radio paths, application of the Meteor Burst Path in commercial communication system is so far limited to a few extent because of its low duty rate, which is, less than several percent at best. In order to get through maximum number of data bits during the short interval of each burst, which normally lives a fractions of a second, a sophisticated communication protocol is called for. In this paper, author introduces a communication protocol which can effectively locate and fetch burst signal by sending out periodic detection signal from master station and, with minimal delay, switch over to transmission states so as to put as many data bits through the detected burst as the burst length permits. By analyzing time period required for each transaction steps, the author derives optimal packet length for various bursts which assures to get a message string through in minimum delay. According to the analysis, the author proposes a protocol including a routine which automatically accesses average length of bursts at each environment and automatically adapt length of data packet so as to maximize data throughput under Riven burst conditions.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.119-124
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• 2001

A new WDM-based protocol for scheduling a variable-length message is proposed in this paper. Two control slots, Pre-reservation slot and Reservation Slot, are used to coordinate transmission and diminish the collisions of packet to minimize the access delay. When there is an idle reservation slot, a control packet is transmitted on that slot and message is transferred. And the node continues to transmit its control packet through the corresponding slot every cycle, until the message is completely transmitted. If an idle reservation slot is not available, the node schedules the transmission time of message in earliest available time using Pre-reservation slots. The proposed scheduling protocol has several advantages; any new node can join the network anytime without network re-initialization. Moreover, with the pre-reservation slots, we can avoid the packet collisions and destination conflicts, and we can improve the access delay time for message transmissions.

• Journal of KIISE:Information Networking
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• v.29 no.3
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• pp.277-285
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• 2002

This paper proposes and analyzes an error control scheme for the transmission control based real-time communication, such as FDDI, TDMA, and wireless LAN, which delivers the message according to the round robin fashion after the off-line bandwidth allocation. Taking into account the time constraint of each message, the proposed error control scheme makes the receiver transmit the error report via asynchronous traffic while the sender resend the requested message via overallocated access time which is inevitably introduced by the bandwidth allocation procedure for hard real -time guarantee. The error control procedure does not interfere other real -time message transmissions. In addition, as each frame contains the size of the message it belongs, the receiver can recognize the end of completion of message transmission. This enables earlier error report to the receiver so that the sender can cope with more network errors. The analysis results along with simulation performed via SMPL show that the proposed scheme is able to enhance the deadline meet ratio of messages by overcoming the network errors. Using the proposed error control scheme, the hard real -time network can be built at cost lower than, but performance comparable to the expensive dual link network.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.2
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• pp.1-8
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• 1999

The present paper describes an approximation for estimation of earthquake-induced hydrodynamic loads in rigid storage tank which accelerated in horizontal direction. The storage tank is vertically cylindrical, and the sectional shape may be circular, rectangular or irregular. The solution for harmonic excitation is studied based on velocity potential theory, and then the time domain solution for earthquake is obtained by using design response spectrum. As a result, earthquake load is influenced primarily by the inertia force of high frequency effective mass of the storage tank, responding to the characteristics of design response spectrum, tank sectional shape, and the ratio of tank base length to depth. Earthquake-induced hydrodynamic loads in rigid storage tank can be effectively obtained by using the high frequency approximation method in case of quite large, or small ratio of the tank base length to water depth.

• Journal of the Korea Concrete Institute
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• v.22 no.1
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• pp.59-68
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• 2010

In the present study, the deformation capacity of slender shear walls with thin web subject to inelastic deformation after flexural yielding was studied. Web-crushing and rebar-fracture were considered as the governing failure mechanisms of walls. To address the effect of the longitudinal elongation on web-crushing and rebar-fracture, the longitudinal elongation was predicted by using truss model analysis. The failure criteria by web-crushing and rebar-fracture were defined as a function of the longitudinal elongation. The proposed method was applied to 17 shear wall specimens with boundary columns, and the prediction results were compared with the test results. The results showed that proposed method predicted the maximum deformations and failure modes of the wall specimens with reasonable precision.

• The KIPS Transactions:PartB
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• v.10B no.5
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• pp.485-490
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• 2003

In this paper, we propose the possibility of introducing chaotic sequences into digital watermarking systems as potential substitutes to commonly used pseudo noise sequences. Chaotic sequences have several good properties including the availability of a great number of them, the ease of their generation, as well as their sensitive dependence on their initial conditions. And the quantization does not destroy the good property. So this paper proposes a method that transforms Hangul text to chaotic sequence. And we presents how the Hangul text is expressed by an implied data and the implied data is regenerated into the original text. In this paper, we use this implied Hangul text for watermarking.