• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.9
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• pp.1436-1443
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• 1989

In this paper, we propose a maximum-likelihood estimation(MLE) method to obtain the location and the amplitude of the pulses in MPE( multi-pulse excitation)-LPC speech synthesis using multi-pulses as excitation source. This MLE method computes the value maximizing the likelihood function with respect to unknown parameters(amplitude and position of the pulses) for the observed data sequence. Thus in the case of overlapped pulses, the method is equivalent to Ozawa's crosscorrelation method, resulting in equal amount of computation and sound quality with the cross-correlation method. We show by computer simulation: the multi-pulses obtained by MLE method are(1) pseudo-periodic in pitch in the case of voicde sound, (2) the pulses are random for unvoiced sound, (3) the pulses change from random to periodic in the interval where the original speech signal changes from unvoiced to voiced. Short time power specta of original speech and syunthesized speech obtained by using multi-pulses as excitation source are quite similar to each other at the formants.

• Journal of the Korean Institute of Telematics and Electronics
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• v.14 no.2
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• pp.1-9
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• 1977

The waveform, power spectrum and optimal receiver structure for fast FSK are analysed. It is shown and verified experimentally that for the observation interval of two bit periods, the bit error rate is as good as that of PSK. At the same time, it is shown to have the advantage of narrower band width than PSK. In experiment, the FFSK signal is generated by using a binary transversal filter and a low pass filter.

• Speech Sciences
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• v.7 no.4
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• pp.3-10
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• 2000

This paper presents a time-based Pitch Determination Algorithm (PDA) for the reliable estimation of Pitch Period (PP) in speech signals. Based on the Dyadic Wavelet Transform (DyWT) , the proposed PDA detects the presence of Glottal Closure Instants (GCI) and uses the information to determine the pitch period. We also examine the problem of conventional PDAs based on DyWT; their performance is compared with the proposition of this paper. The effectiveness of the proposed method is tested with real speech signals containing a transition between the voiced and the unvoiced interval where the energy of the voiced signal is unsteady. The result shows that the proposed method provides good performance in estimating both the unsteady GCI positions as well as the steady parts.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.31B no.11
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• pp.63-77
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• 1994

This paper describes the real-time system which, through analyzing a sequence of images, can extract motional information on a moving object and can contol servo equipment to always locate the moving object at the center of an image frame. An image is a vast amount of two-dimensional signal, so it takes a lot of time to analyze the whole quantity of a given image. Especially, the time needed to load pixels from a memory to processor increase exponentially as the size of an image increases. To solve such a problem and track a moving object in real-time, this paper addresses how to selectively search the spatial and time domain. Based on the selective search of spatial and time domain, this paper suggests various types of techniques which are essential in implementing a real-time tracking system. That is, this paper describes how to detect an entrance of a moving object in the field of view of a camera and the direction of the entrance, how to determine the time interval of adjacent images, how to determine nonstationary areas formed by a moving object and calculated velocity and position information of a moving object based on the determined areas, how to control servo equipment to locate the moving object at the center of an image frame, and how to properly adjust time interval(${\Delta}$t) to track an object taking variable speed.

• International Journal of Aeronautical and Space Sciences
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• v.8 no.1
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• pp.10-20
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• 2007

For spacecraft attitude control, reaction wheel (RW) steering laws with more than three wheels for three-axis attitude control can be derived by using a control allocation (CA) approach.1-2 The CA technique deals with a problem of distributing a given control demand to available sets of actuators.3-4 There are many references for CA with applications to aerospace systems. For spacecraft, the control torque command for three body-fixed reference frames can be constructed by a combination of multiple wheels, usually four-wheel pyramid sets. Multi-wheel configurations can be exploited to satisfy a body-axis control torque requirement while satisfying objectives such as minimum control energy.1-2 In general, the reaction wheel steering laws determine required torque command for each wheel in the form of matrix pseudo-inverse. In general, the attitude control command is generated in the form of a feedback control. The spacecraft body angular rate measured by gyros is used to estimate angular displacement also.⁵ Combination of the body angular rate and attitude parameters such as quaternion and MRPs(Modified Rodrigues Parameters) is typically used in synthesizing the control command which should be produced by RWs.¹ The attitude sensor signals are usually corrupted by noise; gyros tend to contain errors such as drift and random noise. The attitude determination system can estimate such errors, and provide best true signals for feedback control.⁶ Even if the attitude determination system, for instance, sophisticated algorithm such as the EKF(Extended Kalman Filter) algorithm⁶, can eliminate the errors efficiently, it is quite probable that the control command still contains noise sources. The noise and/or other high frequency components in the control command would cause the wheel speed to change in an undesirable manner. The closed-loop system, governed by the feedback control law, is also directly affected by the noise due to imperfect sensor characteristics. The noise components in the sensor signal should be mitigated so that the control command is isolated from the noise effect. This can be done by adding a filter to the sensor output or preventing rapid change in the control command. Dynamic control allocation(DCA), recently studied by Härkegård, is to distribute the control command in the sense of dynamics⁴: the allocation is made over a certain time interval, not a fixed time instant. The dynamic behavior of the control command is taken into account in the course of distributing the control command. Not only the control command requirement, but also variation of the control command over a sampling interval is included in the performance criterion to be optimized. The result is a control command in the form of a finite difference equation over the given time interval.⁴ It results in a filter dynamics by taking the previous control command into account for the synthesis of current control command. Stability of the proposed dynamic control allocation (CA) approach was proved to ensure the control command is bounded at the steady-state. In this study, we extended the results presented in Ref. 4 by adding a two-step dynamic CA term in deriving the control allocation law. Also, the strict equality constraint, between the virtual and actual control inputs, is relaxed in order to construct control command with a smooth profile. The proposed DCA technique is applied to a spacecraft attitude control problem. The sensor noise and/or irregular signals, which are existent in most of spacecraft attitude sensors, can be handled effectively by the proposed approach.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11A
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• pp.882-890
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• 2009

In this paper, we describe a compensation method that can be used for the situation where Loran receivers lose their phase lock to the received Loran signals when Loran signals are employed for the synchronization of national infrastructures such as telecommunication networks, electric power distribution and so on. In losing the phase lock to the received signals in a Loran receiver, the inner oscillator of the receiver starts free-running and the performance of the timing synchronization signals which are locked to the oscillator's phase is very severly degraded, so the timing accuracy under 1 us for a Primary Reference Clock (PRC) required in the International Telecommunications Union (ITU) G.811 standard can not be satisfied in the situation. Therefore, in this paper, we propose a method which can compensate the phase jump by using a compensation algorithm when a Loran receiver loses its phase lock and the performance evaluation of the proposed algorithm is achieved by the Maximum Time Interval Error (MTIE) of the measured data. From the performance evaluation results, it is observed that the requirement under 1 us for a PRC can be easily achieved by using the proposed algorithm showing about 0.6 us with under 30 minutes mean interval of smoothing with 1 hour period when the loss of phase lock occurs.

• Journal of Korean Society of Transportation
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• v.22 no.7 s.78
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• pp.131-137
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• 2004

Conventional traffic signal optimization models assume that green intervals for pedestrian crossings are given as exogenous inputs such as minimum green intervals for straight-ahead movements. As the result, in reality, the green intervals of traffic movements may not distribute adequately by the volume/saturation-flow of them. In this paper, we proposed signal optimization models formulated in BMILP to integrate pedestrian crossings into traffic movements under under-saturated traffic flow. The model simultaneously optimizes traffic and pedestrian movements to minimize weighted queues of primary queues during red interval and secondary queues during queue clearance time. A set of linear objective function and constraints set up to ensure the conditions with respect to pedestrian and traffic maneuvers. Numerical examples are given by pedestrian green intervals and the number of pedestrian crossings located at an arm. Optimization results illustrated that pedestrian green intervals using proposed models are greater than those using TRANSYT-7F, but opposite in the ratios of pedestrian green intervals to the cycle lengths. The simulation results show that proposed models are superior to TRANSYT-7F in reducing delay, where the longer the pedestrian green interval the greater the effect.

• Journal of Sensor Science and Technology
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• v.5 no.2
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• pp.47-54
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• 1996

This paper deals with the electric field sensor and automatic measuring system of the time-varying space electric field produced by lightning discharges. The theoretical principle and the design rule of the measuring devices are investigated, and the semisphere-type electric field sensor and the signal process system are fabricated. From the calibration experiments, the frequency bandwidth of the measuring system ranges from 200 [Hz] to 1.56 [MHz] and the sensitivity is 0.96 [m V/V/m] as the amplification gain is 10. In addition, the electric field waveforms produced by lightning discharges are observed by the proposed electric field measuring system from June to August in 1995. The data is sampled with the time interval of 200 [ns] and is automatically recorded by transient signal analyzer(Necolet Pro 30), the resolution of which is 12 bit. And it is registered at personal computer. The electric field waveforms produced by intracloud discharge tend to be bipolar, with two or three narrow and fast rising pulses superimposed on the initial half-cycle.

• Smart Structures and Systems
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• v.6 no.5_6
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• pp.675-687
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• 2010

Structural Health Monitoring (SHM) is the science and technology of monitoring and assessing the condition of aerospace, civil and mechanical infrastructures using a sensing system integrated into the structure. Impedance-based SHM measures impedance of a structure using a PZT (Lead Zirconate Titanate) patch. This paper presents a low-power wireless autonomous and active SHM node called Autonomous SHM Sensor 2 (ASN-2), which is based on the impedance method. In this study, we incorporated three methods to save power. First, entire data processing is performed on-board, which minimizes radio transmission time. Considering that the radio of a wireless sensor node consumes the highest power among all modules, reduction of the transmission time saves substantial power. Second, a rectangular pulse train is used to excite a PZT patch instead of a sinusoidal wave. This eliminates a digital-to-analog converter and reduces the memory space. Third, ASN-2 senses the phase of the response signal instead of the magnitude. Sensing the phase of the signal eliminates an analog-to-digital converter and Fast Fourier Transform operation, which not only saves power, but also enables us to use a low-end low-power processor. Our SHM sensor node ASN-2 is implemented using a TI MSP430 microcontroller evaluation board. A cluster of ASN-2 nodes forms a wireless network. Each node wakes up at a predetermined interval, such as once in four hours, performs an SHM operation, reports the result to the central node wirelessly, and returns to sleep. The power consumption of our ASN-2 is 0.15 mW during the inactive mode and 18 mW during the active mode. Each SHM operation takes about 13 seconds to consume 236 mJ. When our ASN-2 operates once in every four hours, it is estimated to run for about 2.5 years with two AAA-size batteries ignoring the internal battery leakage.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.2
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• pp.40-47
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• 2008

It is known that the adhesive interface testing of the rocket motor using the ultrasonic wave is superior to the other testing methods about the ability to economical detect the defects. But, the signal analysis of the ultrasonic wave takes a lot of time and efforts because the time interval of the transmitted pulse and the received pulse is too short to separate the reflected signals due to the multi-layers of the rocket motor. The ultrasonic testing of rocket motor have only applied to the automatic system about extremely limited areas like the debond in adhesive interface between the motor case and the insulator. In this study the new technique to detect the debond between the liner and the propellant using the property of the resonance and the lamb waves instead of the existing ultrasonic testing was described.