• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4A
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• pp.377-384
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• 2006

According to fast VoIP technology development, more and more companies change voice network into IP based network among branch offices. IP PBX, which is deployed up to now, composed of IP phone and VoIP Gateway. Every telphone has replaced with If phone which support VoIP and VoIP gateway is installed in PBTN connection point to relay voice data. It can reduce the communication expense of International call, long distance call and call between a headquater and a trance because it uses internet line. In this paper, IP PBX is implemented that can distribute call using PBX network only usig personal terminal without Proxy Server. Depending on Role, terminal can be registered Master, Server and Client and it is verified in terms of performance and validation.

• Journal of Communications and Networks
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• v.15 no.5
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• pp.457-463
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• 2013

In recent days, cooperative diversity and communication security become important research issues for wireless communications. In this paper, to achieve low probability of interception (LPI) and high throughput in the cooperative single-carrier frequency division multiple access (SC-FDMA) system, a new physical layer transmission scheme is proposed, where a new encryption algorithm is applied and adaptive modulation is further considered based on channel state information (CSI). By doing so, neither relay node nor eavesdropper can intercept the information signals transmitted from user terminal (UT). Simulation results show above new physical layer transmission scheme brings in high transmission safety and secrecy rate. Furthermore, by applying adaptive modulation and coding (AMC) technique according to CSI, transmission throughput can be increased significantly. Additionally, low peak-to-average power ratio (PAPR) characteristic can still be remained due to the uniform distribution of random coefficients used for encryption algorithm.

• Journal of Korea Society of Digital Industry and Information Management
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• v.11 no.1
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• pp.97-109
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• 2015

In this paper, we design and implement a two-way automatic communication system using a mobile instant messenger that can provide a customized service through a real-time two-way communication using a mobile instant messaging service. Two-way automatic communication system using a mobile instant messenger can improve the quality and quantity of information in real-time update of the information through the feedback. In addition, since it is communicated by using a mobile Instant Messanger in 1:1 there is no concerns that is recognized as spam, as well as it is possible to provide customized information for each user. Two-way automatic communication system using a mobile instant messanger shows the difference of the speed according to the data input time in typing by hands in result of comparing the time to input a date and the processing speed to search a data. Therefore in category treatment, command processing and natural language processing, Category treatment way is the most excellent in aspect of data processing speed, otherwise in aspect of the total speed to combine the data input time and the processing time, the command processing way is the best method.

• Journal of Communications and Networks
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• v.18 no.3
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• pp.351-363
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• 2016

This paper investigates the performance of interference-limited two-way transmission protocols in the Rayleigh fading channels. New lower bound of outage probability and approximate expression of bit error rate (BER) for three-phase two-way relaying (3P-TWR) protocol are derived in closed-form. These expressions are valid for arbitrary signal-to-noise ratio values, numbers of co-channel interferers and amajority of modulation formats employed in the practical system. Then a comparative study is developed for the performance of three two-way transmission protocols, i.e., direct transmission (DT) protocol, two-phase two-way relaying (2P-TWR) protocol and 3P-TWR protocol based on the asymptotic expressions of outage probability and BER. On the basis of the theoretical results, the thresholds on the strength (variance) of direct channel and target rate for the relative performance of different protocols are obtained and the effect of interferences at the terminal and relay on the relative performance is analyzed. The results present key insights on how to choose proper two-way transmission protocol with the knowledge of fading channels, required date rate and modulation format to optimize the system performance in the practical interference-limited scenarios. Simulation results are presented to validate the theoretical analysis.

• Journal of Korea Society of Digital Industry and Information Management
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• v.15 no.3
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• pp.45-53
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• 2019

Moving image sharing technology has developed various servers and programs for personal broadcasting. In this paper, we propose the method of transmitting the multiple moving image, including the output channel of external streaming server. It also implements and tests multiple real-time broadcast channel automatic transmission systems that assign multiple output channels to automatic output channels. As a result of the experiment, it is easy to allocate moving image to broadcast channels that are output through the external streaming server's output channels regardless of the size of the streaming server, enabling the management of efficient output channels at the time of transmission of multiple moving image. The moving image can be provided through streaming method regardless of the type of moving image from the moving image provider terminal, and the moving image transmission can be controlled in various ways, including adding and changing channels for which the moving image is sent, and sending delayed to the moving image.

• Journal of the Society of Disaster Information
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• v.16 no.2
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• pp.402-410
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• 2020

Purpose: The purpose of this research is to eliminate communication shadowing loss of the 'smart safety management system'. The 'smart safety management system' can monitor and relay real time data of workers working in high risk workplace (i.e: industrial scene, disaster scene). The data will provide the rescue team the 'golden hour' in their rescue operations. Method: In this research, safety tag was designed and implemented so that it acts as a repeater for the user. Result: In other words, when communication in-between the safety tag and headquarters' communication terminal is jeopardized, the safety tag will act as a repeater-terminal for other safety tags in the area. Conclusion: The research tested if a specific building with communication shadowing loss problem was resolved when safety tags were implemented. Communication shadowing was first identified in-between the safety tag and headquarters' communication terminal. When extra safety tags were deployed in the same situation, the results showed that the communication shadowing loss was resolved. The repeater safety tags could resolve communication shadowing loss of up to three basement levels in this test building.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.5
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• pp.11-16
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• 2012

Opportunistic transmit cooperative relaying (OTR) system has been interested for its ability to mitigate the fading in wireless channel without multiple antennas in a small terminal. In OTR system, only the relays that the received Signal-to-noise ratio (SNR) from a source is greater than the threshold transmit to the destination. However, the receiving branches of a destination in a realistic system is fixed, the excess number of signals from the transmit relays does not improve the system performance and consequently increases power consumption. In this paper, we adopt Double Opportunistic Transmit (DOT) cooperative diversity system which controls the average number of transmit relays. Although the average number of the transmit relays can be controlled by adjusting the two thresholds in DOT system, the instantaneous number of transmit relays is varying in fading channel. Thus we propose Maximal Ratio Combining (MRC) or Generalized Selection Combining (GSC) according to the number of the signals from relays at the destination. The outage probability of the proposed system is derived in closed form. The analytical results show that the system performance is improved with the number of the branches. Also it is noticed that when the number of the branches is fixed, the outage probability decreases with the increase of the average SNR of S-R path and R-D path.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.10
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• pp.724-739
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• 2009

This paper suggests the energy-efficient message delivery scheme and the software platform which exploits the multiple network interfaces of the mobile terminals and GPS in the current mobile devices. The mobile terminals determine the delivery method among 'direct', 'indirect', and 'WAN' based on the position information of itself and other terminals. 'Direct' method sends a message directly to the target terminal using local RAT. 'Indirect' method extends the service area by exploiting intermediate terminals as relay node. If the target terminal is too far to reach through 'direct' or 'indirect' method, the message is sent using wireless WAN technology. Our proposed scheme exploits the position information and, thus, power consumption is drastically reduced in determining handover time and direction. Network simulation results show that our proposed delivery scheme improves the message transfer efficiency and the handover detection latency. We implemented a message platform in a smart phone realizing the proposed delivery scheme. We compared our platform with other typical message platforms from energy efficiency aspect by observing the real power consumption and applying the mathematical modeling. The comparison results show that our platform requires significantly less power.

• Journal of Internet of Things and Convergence
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• v.6 no.1
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• pp.97-102
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• 2020

Multi-Channel Switch ICs for IoT have integrated several solid state structure low ON-resistance bi-directional relay MOS switches with level shifter to drive high voltage and they should be independently controlled by external serialized logic control. These devices are designed for using in applications requiring high-voltage switching control by low-voltage control signals, such as medical ultra-sound imaging, ink-jet printer control, bare board open/short and leakage test system using Kelvin 4-terminal measurement method. This paper describes implementation of analog switch control block and its verification using Field programmable Gate Array (FPGA) test pattern generation. Each block has been implemented using Verilog hardware description language then simulated by Modelsim and prototyped in a FPGA board. Compare to conventional IC, The proposed architecture can be applied to fields where multiple entities need to be controlled simultaneously in the IoT environment and the proposed pattern generation method can be applied to test similar types of ICs.

• The Journal of the Korea Contents Association
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• v.6 no.1
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• pp.8-13
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• 2006

In this thesis, an automatic door lock system using a dual tone multiple frequency(DTMF) signal generated as pushing the key button of mobile phone is proposed and implemented. This system consists of a transmitter module and a receiver module for processing the DTMF signal of mobile phone. The DTMF signal of mobile phone connected with ear-phone jack enter into the input terminal of DTMF receiver and those are encoded by a code-converter with 4-bits binary format in the DTMF receiver. The encoded output signals are transmitted to the amplitude shift keying(ASK) modulator of transmitter module and the modulated ASK signals which are converted into radio frequency(RF) signals propagate in a free space. The RF signals passed through a free space are demodulated by the ASK demodulator of receiver module and the demodulated ASK signals are sent to a micro-controller unit(MCU). The output signals processed by the MCU are compared with the secreted identification number which is prerecorded in a microprocessor and are transferred to a power relay. If the result is the same, the automatic door lock system opens a door. In the opposite case, it maintains closing the door. The implemented automatic door lock system operates well in mobile environments.