• ETRI Journal
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• v.45 no.5
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• pp.768-780
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• 2023

The application of unmanned aerial vehicles (UAVs) has recently attracted considerable interest in various areas. A three-dimensional multiple-input multiple-output concentric two-hemisphere model is proposed to characterize the scattering environment around a vehicle in an urban UAV-to-vehicle communication scenario. Multipath components of the model consisted of lineof-sight and single-bounced components. This study focused on the key parameters that determine the scatterer distribution. A time-variant process was used to analyze the nonstationarity of the proposed model. Vital statistical properties, such as the space-time-frequency correlation function, Doppler power spectral density, level-crossing rate, average fade duration, and channel capacity, were derived and analyzed. The results indicated that with an increase in the maximum scatter radius, the time correlation and level-crossing rate decreased, the frequency correlation function had a faster downward trend, and average fade duration increased. In addition, with the increase of concentration parameter, the time correlation, space correlation, and level-crossing rate increased, average fade duration decreased, and Doppler power spectral density became flatter. The proposed model was compared with current geometry-based stochastic models (GBSMs) and showed good consistency. In addition, we verified the nonstationarity in the temporal and spatial domains of the proposed model. These conclusions can be used as references in the design of more reasonable communication systems.

• East Asian mathematical journal
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• v.30 no.1
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• pp.23-29
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• 2014

To solve inefficient spectrum usage problem under current static spectrum management policy, various kinds of dynamic spectrum access strategies have appeared. Myopic policy, which maximizes immediate throughput, is a simple and robust strategy with reduced complexity. In this paper, we present a simple mathematical model to evaluate the saturation throughput and medium access delay of a myopic policy in the presence of multiple channels.

• Journal of the Korean Institute of Intelligent Systems
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• v.2 no.2
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• pp.42-60
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• 1992

An adaptive fuzzy system can efficiently classify subimages into four categories according to image activity level for image data compression. The system estimates fuzzy rules by clustering input-output data generated from a given adaptive transform image coding process. The system encodes different images without modification and reduces side information when encoding multiple images. In the second part, a fuzzy system estimates optimal bit maps for the four subimage classes in noisy channels assuming a Gauss-Markov image model. The fuzzy systems respectively estimate the sampled subimage classification and the bit-allocation processes without a mathematical model of how outputs depend on inputs and without rules articulated by experts.

• Journal of information and communication convergence engineering
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• v.3 no.3
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• pp.119-121
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• 2005

This paper aims to estimate the delay time of multiple signals in a multi-path environment. It also seeks to carry out a comparative analysis with the existing delay time under the proposed algorithm to develop a new algorithm that applies the space average method in a MUSIC algorithm. Unlike the existing delay time estimation algorithm, the developed algorithm was able to estimate the delay time in 5ns low. Therefore, the algorithm proposed in this paper improved the existing delay time estimated algorithm.

• MALSORI
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• no.48
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• pp.81-91
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• 2003

In this paper, we propose a speech recognition method based on independent component analysis (ICA) and spectral enhancement techniques. While ICA tris to separate speech signal from noisy speech using multiple channels, some noise remains by its algorithmic limitations. Spectral enhancement techniques can compensate for lack of ICA's signal separation ability. From the speech recognition experiments with instantaneous and convolved mixing environments, we show that the proposed approach gives much improved recognition accuracies than conventional methods.

• Proceedings of the Korea Society of Environmental Toocicology Conference
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• 2001.05a
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• pp.140-140
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• 2001

Porins are major outer membrane proteins which produce non-specific aqueous channels across the membrane that permit the diffusion into the bacterial cells of hydrophilic compounds including sugars, amino acids, and antibiotics. In some gram-negative organisms, antibiotic resistance can be induced by mutational loss of channel that causes a decrease in outer membrane permeability. (omitted)

• Proceedings of the Korean Information Science Society Conference
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• 2012.06d
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• pp.187-189
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• 2012

The medium access control (MAC) protocol is designed only for single channel in the IEEE 802.11 standard. That means the throughput of the network is limited by the bandwidth of the single channel. The multiple channels can be exploited to get more concurrent transmission. In this paper, we propose a novel Multi-channel MAC that utilizes the channel more efficiently than other Multi-channel MAC protocols.

• Journal of Communications and Networks
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• v.7 no.3
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• pp.278-283
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• 2005

This paper proposes a blind channel estimation scheme for long code direct sequence code division multiple access (DS­CDMA) systems with multipath fading channels. This scheme combines the advantages of Toeplitz displacement and correlation matching methods to achieve improved performance. The basic idea is to remove the effects of noise and interferences with Toeplitz displacement operation and then estimate the multi path channel parameters with the correlation matching method. Simulation results are presented to show that the proposed scheme provides better MSE performance and robustness against the near-far problem.

• Proceedings of the IEEK Conference
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• 2001.06a
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• pp.121-124
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• 2001

In this paper, we propose a robust trellis coded OFDM(orthogonal frequency division multiplexing) system for wireless communications over frequency selective fading channels. Computer simulations show that the proposed system achieves the better frame error rate(FER) performance as compared with the conventional Space time coded OFDM system in the correlated channel with multiple transmitter antennas.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2003.07a
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• pp.11-16
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• 2003

본 논문에서는 새로운 공개키 다중채널 broadcast encryption scheme(이하 PK-MCBE라 부른다)을 제안한다. 일반적인 broadcast encryption은 하나의 채널스트림을 전송하는 반면 PK-MCBE는 다수채널의 컨텐츠 스트림을 전송한다. 본 논문에서 제안하는 방식에서 수신자는 단지 하나의 비밀키만을 필요로 하며 한번 받은 비밀키는 변경되지 않는다. 제안하는 방식에서는 각 채널당 송신자가 전송하는 메세지의 공통부분을 한번만 전송하여 전체 전송 메세지의 길이를 줄일 수 있다. 또한 배신자(traitors)를 추적하여 효과적으로 강제 탈퇴시킬 수 있다.