• Bulletin of the Korean Chemical Society
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• v.18 no.12
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• pp.1281-1285
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• 1997

The time-dependent tracking inversion method is developed to extract the potential of the excited state from frequency-domain measurements, such as the absorption profile. Based on the relay of the regularized inversion procedure and time-dependent wave-packet propagation, the algorithm extract the underlying potential piece by piece by tracking the time-dependent data which can be synthesized from frequency-domain measurements. We have demonstrated the algorithm to extract the potential of excited state for a model diatomic molecule. Finally, we describe the merits of the time-dependent tracking inversion method compared to the time-dependent inversion and discuss several extensions of the algorithm.

• Journal of IKEEE
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• v.18 no.4
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• pp.502-508
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• 2014

This paper has reviewed the performances of various AGCs which can be adopted in IEEE802.11p modems. IEEE802.11p, a high speed mobile communication standard for vehicles, requires high performance signal detector since the channel impulse responses are varied rapidly in time. In order to select the optimal signal detector, we simulated the performances of three detection methods. One is using RSSI signal, the other is using RSSI signal and I/Q signal, and the third is using I/Q signal through the Monte Carlo simulation. We evaluated the performances of the algorithms using our own system based on MAX 2829 transceiver(MAXIM $Integrated^{TM}$) in a real vehicular environment. As a result, the experiment using Fully I/Q signal derives the most excellent performance with the lowest minimum receiver sensitivity, packet error rate (PER) and false alarm rate (FAR).

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.4
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• pp.78-85
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• 2011

In vehicle ad-hoc network (VANET) environments, traffic related information such as accident information, emergency information and real time traffic condition have to be delivered to on-board-unit (OBU) or/and road-side-equipment (RSE) for preventing traffic accidents in advance. In this paper, we introduce a Multi-Channel MAC (MCM) since the existing single channel operation may cause packet transmission delay and unexpected communication failure. To offer a seamless safety message transmission during the various services, it is necessary to manage the MAC scheduler in wireless access in vehicular environments (WAVE) systems. The MCM consists of MAC softwares and MAC hardwares where the former and the later ones are implemented with real time operation system based C language and FPGA module with VHDL language, respectively. The performance and QoS are verified by practical measurements and compared with the scheme using single channel operation.

• Journal of Advanced Navigation Technology
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• v.5 no.2
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• pp.158-164
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• 2001

We presented a channel model for the inter vehicle radio link including the reflection from the road surface, side road vehicle and concrete wall. Then we theoretically derived the path loss and delay profile characteristics using the Ray tracing method efficiently analyzing millimeter wave or optic wave. Finally, we shown the improvement of propagation characteristics by diversity techniques, BCH coding and convolution coding techniques. At the result, MRC diversity techniques and BCH coding can't obtained PER = $10^{-6}$ which is considered to be data service criterion. But, we knew that Packet Error Rate Characteristic can obtained PER = $10^{-6}$, which is considered to be data service criterion, when convolution coding scheme are adopted in Rician fading.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.3
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• pp.1031-1046
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• 2018

Vehicular ad hoc network (VANET) is a dedicated network to connect vehicles without any centralized administration or infrastructure. The wireless access in vehicular environments (WAVE) protocol leveraging IEEE 1609/802.11p is widely implemented for VANETs. However, in congested traffic situation, the performance of the WAVE system degrades significantly due to serious collision, especially for safety related broadcast services on the control channel (CCH) interval due to the inherent drawback of its collision avoidance mechanisms called carrier sense multiple access with collision avoidance (CSMA/CA). In this paper, we propose a method that can decrease the number of frame collisions in CCH with a few modifications to the IEEE 802.11p protocol. In the paper, vehicles still employ CSMA/CA to compete for the channel access opportunity. However, by taking advantage of periodicity of synchronization interval, a two-state switching scheme introducing two new inter frame space (IFS) is proposed to reduce the number of competing vehicles substantially and as a result, the collision probability is significantly decreased. The simulation results demonstrate the superiority of the proposed method in packet collision rate.

• Journal of Korea Multimedia Society
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• v.17 no.10
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• pp.1220-1228
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• 2014

Emergency Warning Service will be the most important service of VANET. Transmission delay is the most important performance criteria of the warning service. Most legacy research takes a way to minimize the packet collision. However those approach has a critical weak point on urban environment where there is a blind area of electric wave. So another issue is required in order to provide enhanced warning message propagation technique to overcome the urban environment problem. In this paper, I proposed an enhanced warning message propagation scheme in the poor electric wave environment as the intersection area. Proposed scheme forwards the warning message to the blind area by enhanced forwarding node selection technique. For efficiency of warning message propagation, I suggest forwarding priority for decision of forwarding node. And the node has a direct mode or redirect mode depending on neighbor nodes. The simulation was carried out to evaluate the performance. The simulation results show that proposed scheme has the superior performance compared to legacy warning message technique.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.45.3-46
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• 2018

Oscillations in a sunspot are easily detected through the Doppler velocity observation. Although the sunspot oscillations look erratic, the wavelet analysis show that they consist of successive wave packets which have strong power near three or five minutes. Previous studies found that 3-min oscillation at the chromosphere is a visual pattern of upward propagating acoustic waves along the magnetic field lines. Resent multi-height observations help this like vertical study, however, we also focus on horizontal facet to extend three dimensional understand of sunspot waves. So, we investigate a fragmented sunspot expected to have complex wave profiles according to the positions in the sunspot observed by the Fast Imaging Solar Spectrograph. We choose 4 points at different umbral cores as sampling positions to determine coherence of oscillations. The sets of cross-correlation with three and five minutes bandpass filters during a single wave packet reveal interesting results. Na I line show weak correlations with some lags, but Fe I and Ni I have strong correlations with no phase difference over the sunspots. It is more remarkable at Ni I line with 3-min bandpass that all sets of cross-correlation look like the autocorrelation. We can interpret this as sunspot oscillations occur spontaneously over a sunspot at photosphere but not at chromosphere. It implies a larger or deeper origin of 3-min sunspot oscillation.

• Journal of the Korean Vacuum Society
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• v.19 no.6
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• pp.467-474
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• 2010

Packet propagation and absorption for the 28 GHz superconducting ECRIS under developing by KBSI Pusan center is analyzed with limited parameter range. The microwave power generated by 28 GHz gyrotron is axially injected to the plasma cavity through waveguide system. According to the analytical ray tracing calculation, the wave packet launched quasi-longitudinally at a high magnetic field side changes its direction from outward to inward as it is approaching resonance layer. Therefore, initially diverging wave does not likely hit a conducting surface before absorbing by electron cyclotron resonance. Also, absorption by plasma with moderate electron density is so strong that reflection by an extraction plate may not be expected.

• Journal of Advanced Navigation Technology
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• v.15 no.6
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• pp.1059-1067
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• 2011

Next-Generation ITS environment requires high-speed data packet transmission, security, authentication, and hand-over supportable for driving vehicle on road by installing RSEs and OBUs. Therefore, wireless communication technology for next-generation ITS services are advancing to 200km/h maximum speed supportable, 1km communication radius, minimum 10Mbps hish-speed datarate for multimedia data(such as text, images, movie clips and so on) supportable, high reliability. In this paper, we implemented WAVE communication system which based on IEEE 802.11p PHY/MAC and evaluated that the system meets next-generation ITS environments.

• Smart Structures and Systems
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• v.6 no.7
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• pp.835-849
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• 2010

This study investigated propagation characteristics of piezo-activated guided waves in an aluminium rectangular-section tube for the purpose of damage identification. Changes in propagating velocity and amplitude of the first wave packet in acquired signals were observed in the frequency range from 50 to 250 kHz. The difference in guided wave propagation between rectangular- and circular-section tubes was examined using finite element simulation, demonstrating a great challenge in interpretation of guided wave signals in rectangular-section tubes. An active sensor network, consisting of nine PZT elements bonded on different surfaces of the tube, was configured to collect the wave signals scattered from through-thickness holes of different diameters. It was found that guided waves were capable of propagating across the sharp tube curvatures while retaining sensitivity to damage, even that not located on the surfaces where actuators/sensors were attached. Signal correlation between the intact and damaged structures was evaluated with the assistance of a concept of digital damage fingerprints (DDFs). The probability of the presence of damage on the unfolded tube surface was thus obtained, by which means the position of damage was identified with good accuracy.