• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.8
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• pp.33-41
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• 2007

The IEEE 802.11 DCF channel access function allows single transmission inside two-hop network in order to avoid collisions and eliminate the hidden and exposed terminal problems. Singular transmission capability causes data frames waiting for the entire roundtrip time in the transmitter neighborhood, and results in increased frame latency and lower network throughput. Real-time and pervasive applications are severely affected for the lower medium utilization; especially with high network traffic. This work proposes a new scheme with the help of Frame Aggregation technique in IEEE802.11n and overcomes the single transmission barrier maintaining the basic DCF functionality. Proposed scheme allows parallel transmissions in non-interfering synchronized slots. Parallel transmissions bypass the conventional physical carrier sense and random Backoff time for several cases and reduce the frame latency and increase the medium utilization and network capacity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9A
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• pp.991-997
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• 2004

In this paper, we propose the architecture of modem receiver to fabricate HomePNA 2.0 chip. HomePNA suffers from inferior channel because of bridge tap, the effect of amateur HAM band and so on. To transfer data over such channel, HomePNA 2.0 uses training sequence to equalize channel and uses FD-QAM optionally as modulation method. So modem receiver demodulate QAM based signal and needs optimum architecture that fully uses these transmission feature. As a result of research, we define 2 mode function of modem receiver depending on TX/RX state. In this paper, particularly, we show the algorithm of equalizer, carrier phase recovery and frame synchromzationblock and propose architecture that improve the performance of channel equalization and is stable in operation. In the end, we estimate the performance of proposed HomePNA2.0 modem receiver over HomePNA TEST LOOP using SPW program.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.1 no.1
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• pp.55-64
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• 2003

In this study, the maintenance process by the servo manipulator has been developed for the parts of the equipment, which we unable to reach out by the Master-Slave Manipulator(MSM) in a hot cell. To do this, a virtual mock-up is implemented using the iか prototyping technology. Using this mock-up, the workspace of the manipulators in the hot cell and the operator's view through the wall-mounted lead glass have been analyzed. In addition, the path planning of the servo manipulator using the collision detection function of the virtual mock-up has been established. From these, the maintenance process for the parts of the equipment, which are located at the outside of the MSM's workspace using the servo manipulator has been proposed and verified through the graphic simulation. It is revealed that the proposed remote maintenance process of the equipment can effectively be used in the real hot cell operation. It is also believed that the implemented virtual mock-up of the hot cell can effectively be applied in analyzing the various hot cell operation and enhancing the reliability and safety in a hot cell remote handling for the spent fuel management.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.337-344
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• 2003

In this study, the maintenance process by the servo manipulator for the parts of the equipment that cannot be reached by MSM in the hot cell was developed. To do this, the virtual mock up is implemented using virtual prototyping technology. And, Using this mock-up, the workspace of the manipulators In the hot cell and the operator's view through the wall-mounted lead glass are analyzed. And the path planning of the servo manipulator using the collision detection of the virtual mockup is established. Also, the maintenance process for the parts of the equipment that are located out area of the MSM's workspace by the servo manipulator is proposed and verified through the graphic simulation. The proposed remote maintenance process of the equipment can be effectively used in the real hot cell operation. Also, the implemented virtual mock-up of the hot cell can be effectively used in analyzing the various hot cell operation and in enhancing the reliability and safety of the spent fuel management.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.6
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• pp.1115-1120
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• 2004

In this paper, a CSSMA/AI MAC protocol for data services in packet CDMA network is presented. The main features of this protocol are the code status sensing and code reservation for reducing the packet collision. The base station broadcasts the code status on a frame-by-frame basis just before the beginning of each preamble transmission, and the mobile station transmits a preamble for reserving a randomly selected code based on the received code status. After having transmitted the preamble, the mobile station listens to the downlink of the selected code and waits for the base station reply. If this reply indicates that the code has been correctly acquired, it continues the packet transmission for the rest of the frame. If there are other packets waiting for transmission, the base station broadcasts the status of the code as reserved, and the mobile station transmits a packet on a reserved code for the successive frames.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.12
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• pp.2839-2846
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• 2014

New VHF band for use in VDE is determined by WRC-12 due to the overload of AIS VDL, and the system characteristics of the VDE is recommended as ITU-R M. 1842-1. CS-TDMA, a multiple access method of AIS class B, is recommended as that of the VDE. It is inefficient for CS-TDMA just applying the report interval used in AIS class B to transmit high speed data with higher payload in the aspect of efficiency. In this paper, a simulation is executed in order to determine adequate report interval according to the number of active ships that affects directly network traffic. To this end, the performance of CS-TDMA, which includes the number of received packets, reception success rate, channel utilization, and collision rate, is investigated via a simulation.

• The Journal of Information Technology
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• v.7 no.3
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• pp.37-45
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• 2004

The representative communication method which is applied in the low-speed power line communication modem with 60bps is single carrier method. It has been used mainly for the control. The single carrier method is very sensitive to a power line communication channel environment. Specially, the severe attenuation of the transmission signal according to the notch characteristics of channel becomes the main cause of communication error. Domestic power line channel environment has this notable feature. In this paper, we implemented the low-speed power line communication system which used the chirp signal method to be strong in notch and noise characteristics. In this research, we proposed the method which transmits 1- '1 Unit symbol Chirp signal' with a 100${\mu}s$ time within 1ms for 1 bit. Also it applied for the Convolution code for an error correction and the Manchester code for a collision perception and an error detection. It used the method which uses the bit correlator for signal detection in the receiver parts. We confirmed that the communication method of the chirp method has a excellent performance compared to single carrier methods with a result of experiment of the low-speed power line communication system with the 60bps.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.2
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• pp.99-113
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• 1992

In general, TDMA and FDMA have been used for multiple access communication methods. Recently. However, ALOHA and CSMA protocols came to exist as new schemes for VSAT data networks and LANs, respectively. These schemes are proven to be effective for packet switched communication systems that has bursty traffic but packet collisions. In this paper we analyze capture statistics arising from fading channels in packet radio communication systems in the context of ALOHA protocol. We derive general results of the exact form of capture probabilities and present numerical data for wide range of fading parameters. Since the capture probabilities are found to approach zero when the number of transmitted signals become larger, we are able to determine the achievable channel throughput by a least squares fitting of an exponential-type function to the probabilities.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.7B
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• pp.686-693
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• 2009

In this paper, we propose an efficient tag sleep method utilizing empty time slots for improving the tag collection performance in active RFID systems. In the proposed tag sleep method, the reader detects the occurrence of empty time slots by carrier sensing and utilizes the wasted empty time slots to transmit sleep commands to the collected tags throughout the framed slotted aloha-based tag collection process, resulting in reducing the time required for tag collection. Via the simulation experiments, we evaluated the performance of the tag collection applied with the proposed tag sleep method, compared with that of the basic tag collection. The simulation results showed that the tag collection applied with the proposed tag sleep method could reduce the average tag collection time by 12.28%, 12.30%, and 13.31 %, for the framed slotted aloha with the fixed 128 time slots and 256 time slots, and the dynamic framed slotted aloha anticollision protocols, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.4B
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• pp.391-398
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• 2011

In this paper, we propose a MAC protocol for visible light wireless LAN using LED light. The proposed MAC protocol has a function of automatic direction optimization for LED transceiver. There is periodical time slot for broadcasting and registration in the proposed MAC protocol. We used polling method for data transfer in the protocol since visible light is hard to detect carrier and collision by other mobile stations; thus we cannot use CSMA/CD method in visible light LAN. We also amended the MAC frame of IEEE 802.11 to propose a revised version for visible light wireless LAN using LED light. We investigate the performance of the proposed MAC protocol. When the bit rate of physical layer is 100 Mb/s, the net data throughput using the proposed MAC protocol is estimated to 94.386 Mb/s.