• Proceedings of the Korea Contents Association Conference
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• 2008.05a
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• pp.69-73
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• 2008

In this paper, analytical methods for calculating the average probability of bit error of time hopping pulse position modulation ultra wideband (TH-PPM UWB) system are given. For the multi-user DS-PAM UWB system, the bipolar pulse amplitude modulation is used in order to achieve better performance. As we know, more attention is paid to the TH-PPM UWB systems recently. In this paper, we first introduce the accurate BER calculation methods of the multi-user TH-PPM UWB systems and then give the performance analysis over the ideal AWGN channel and a correlation receiver. Furthermore, we also introduce their applications in image transmission and data transmission and give the simulation results. The analytical method yields simple and exact formulas relating the performance to the system parameters.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.934-937
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• 2003

Glasses in the system $CuO-P_2O_5-V_2O_5$ were prepared by a press-quenching method on the copper plate. The glass-ceramics from these glasses were obtained by post-heat treatment, and the crystallization behavior and DC conductivities were determined. The conductivities of the glasses were range from $10^{-6}s.Cm^{-1}$ at room temperature, but the conductivities of the glass-ceramics were $10^{-3}s.Cm^{-1}$ increased by $10^3$ order. The crystalline product in the glass-ceramics was $CuV_2O_6$. Heat-treatment conditions influenced the crystal growth of $CuV_2O_6$ and conductivity. The linear relationship between in (${\sigma}T$) and $T^{-1}$ suggested that the electrical conduction in the present glass-ceramics would be due to a small polaron hopping(SPH) mechanism.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.5
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• pp.527-536
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• 2021

In wireless environments, wideband receivers are used in a communication intelligent system to detect unknown signals and obtain azimuth information. To design a wideband receiver that performs multiple signal detection and direction finding simultaneously, it is necessary to consider a reception structure composed of multiple channels. In this paper, we propose a wideband multi-channel receiver for direction finding of unknown wideband communication signals including frequency hopping signals. A signal processing method for detecting received signals and estimating azimuth information is presented, and components of the manufactured wideband receiver are described. In addition, test results of the signal detection performance by mounting the proposed wideband multi-channel receiver on the flight system are included.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.10
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• pp.914-924
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• 1991

It has been generally used for PLL(Phase Locked Loop) to be synthesized randomly chosen frequency state, but the PLL locking time was inevitable element. A direct digital synthesizer. Which makes output frequency directly in sine wave by a phase accumulating method, could be leiminate the defect, although a phase distortion in frequency spectrum. In order to improve this disadvantage, the phase accumulating method is reconsidered in the side of he output wave formula expression. A new mechanism is proposed, and it is constructed by a most suitable logic elements. The spectrum of synthesized sine waveform is simulated and compared with a measured value, and it’s the coherence frequency hoppong state with the PN(Pseudo Noise) code sequence is confirmed. In this results, the power levels of phase distortion harmonics are decreased to 10~25dB and bandwidths are increased to 420kHz.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.1
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• pp.225-234
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• 2019

Bitcoin is a cryptocurrency with characteristics such as de-centralization and distributed ledger, and these features are maintained through a mining system called "proof of work". In the mining system, mining difficulty is adjusted to keep the block generation time constant. However, Bitcoin's current method to update mining difficulty does not reflect the future hash power, so the block generation time can not be kept constant and the error occurs between designed time and real time. This increases the inconsistency between block generation and real world and causes problems such as not meeting deadlines of transaction and exposing the vulnerability to coin-hopping attack. Previous studies to keep the block generation time constant still have the error. In this paper, we propose a machine-learning based method to reduce the error. By training with the previous hash power, we predict the future hash power and adjust the mining difficulty. Our experimental result shows that the error rate can be reduced by about 36% compared with the current method.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4D
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• pp.547-553
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• 2011

This study has redefined the concepts of mobility indexes and potential demand, standards to evaluate areas with the worst public transportation system and applied the relevant indexes to select the areas with the worst public transportation mobility and present a method to set direct public transportation lines between these regions. The mobility indexes and indexes to evaluate potential demand were applied to select the regions with the worst public transportation systems in four metropolitan cities and case studies were carried out on direct lines provided between these regions. The analysis results showed that in public transportation mobility blind spots, public transportation takes much longer than driving an automobile or public transportation services are not provided. In addition, the analysis showed that a direct lines system to solve such worst off regions should be built to have public transportation take as much time as driving an automobile by establishing lines for automobiles only, minimize time lost from hopping up and down a bus and maximize connections.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.11
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• pp.2178-2187
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• 2015

Bluetooth Low Energy (Bluetooth LE) is a representative break-through communication technology for wireless personal area networks on nowaday. In this environment, most of significant performance should be aiming to energy efficiency due to the policy for manufacturing light-weighted communication devices derived from requirement of world IoT market, and many researches have been developed to satisfy this requirement. While Bluetooth LE has been leading the low power communication technology required from the current market by employing duty cycle and frequency hopping approaches, it couldn't address the problem of reliability on broadcast transmissions. The main goal of this paper is aiming to addressing this problem by suggesting a new method. Furthermore analytic evaluations would also be proceeded to find objective results in the view point of broadcast transmission efficiency from Master device.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.2
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• pp.271-279
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• 2008

In this paper, we investigate interference between short-range radiocommunication devices(SRDs) with frequency hopping spread spectrum(FHSS) and direct sequence spread spectrum(DSSS) methods when they are in the same frequency bands. In order to analyze interference from unwanted emission of SRD with DSSS to that of FHSS, Monte-carlo(MC) simulation method is employed and interference probabilities are calculated. We simulate interference scenarios in accordance with several duty cycles and bandwidths. It is also assumed that the propagation model is free space. The effect of distance between interfering transmitter and victim receiver is analyzed and bit error rate(BER) is simulated. From the interference analysis results, it is shown that duty cycle affects compatibility more than band-width does. Also, we can make sure of the separation distance which satisfies BER criterion when there are only one interfering transmitter and multiple interfering transmitters.

• The Journal of the Korea Contents Association
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• v.8 no.4
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• pp.273-284
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• 2008

Movements are a critical ability to young children's whole development, including physical, social/emotional, and cognitive development. This paper proposes the method to estimate movements suitable for young children's body conditions. The proposed method extracts a silhouette in each frame of videos that are obtained by deploying two video cameras by compensating illuminations, removing background and conducting morphology operations. And we extract silhouette feature values: an area, the ratio of length to width, the lowest foot position, and 7 Hu moments. Also, the area and movements of sub-area are used as local features. For motion estimation, we used probability propagation of the features extracted from the front and side frames. The proposed estimation algorithm is demonstrated for seven movements, walking, jumping, hopping, bending, stretching, balancing, and turning.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.12
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• pp.1315-1320
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• 2015

In this paper Communication data link equipment on a high speed-hopping method to use the frequency resources efficiently for the frequency environment is introduced such as sensing techniques, using the same frequency band by using the received two-channel technique and the receive filter bank unit applied to be shared with other equipment such as radar and so on. The real-time measurement and analysis were operated for measurement the frequency environment of the operating band in advance. and primarily equipment to develop is analyzed how the interference effect to the radar minimize the operation of radar equipment. In reverse, to use the same frequency band the methods such as frequency sharing techniques are presented in this paper. Finally, by design of the main items of the RF transceiver NF, transmission output, and a simulation of the IMD, such as whether the key is verified prior to meet specifications.