• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.3
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• pp.524-531
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• 1997

A novel optical cell compressor for optical time division multiplexing system is presented. The compressor is capable of generating optically compressed very high bit-rate (possibly several tens of Gb/s) signals with minimum hardware. Contrast to the previously reported optical compressor, the compressor is mainly composed of passive optical devices and requires no synchronization among control signals in the process of compression, which results in simple implementation. We demonstrate a generation of optically compressed 6 Gb/s optical cells to confirm the fundamental operation of the compressor.

• Journal of Navigation and Port Research
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• v.36 no.6
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• pp.475-480
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• 2012

In order to establish eLoran (enhanced Long Range Navigation) system, it needs the advancement of receiver, transmitter, data channel addition for Loran information, differential Loran sites for compensating Loran-c signal and ASFs (Additional Secondary Factors) database, etc. In addition, the precise synchronization of transmitting station to the UTC (Coordinated Universal Time) is essential if Loran delivers the high absolute accuracy of navigation demanded for maritime harbor entrance. For better timing synchronization to the UTC among transmitting stations, it is necessary to measure and monitor the transmission delay of the station, and the correction information of the transmitting station should be provided to the user's receivers. In this paper we presented the measurement method of absolute delay of Pohang Loran transmitting station and developed a time delay measurement system and a phase monitoring system for Loran station. We achieved -2.23 us as a result of the absolute phase delay of Pohang station and the drift of Loran pulse of the station was measured about 0.3 us for a month period. Therefore it is necessary to measure the delay offset of transmitting station and to compensate the drift of the Loran signal for the high accuracy application of PNT (Positioning, Navigation and Timing).

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.5
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• pp.95-103
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• 2009

An efficient symbol time synchronization scheme for IEEE 802.11n MIMO-OFDM based WLAN systems using cyclic shift diversity (CSD) preamble is proposed. CSD is used to prevent unintentional beamforming when the same preamble signal is transmitted through transmit antennas. However, it is difficult to find a proper starting-point of the OFDM symbol with the conventional algorithms because of time offset by multi-peaks which are result from cross-correlation of received CSD preamble with a known short training symbol. In addition, the performance of symbol time sync. is affected by AGC and packet detection position. In this paper, an optimal symbol time synch. algorithm which is composed of the boundary detection scheme between LTS and OFDM symbols, the verification scheme for enhancement of boundary detection accuracy, and the SNR-varying threshold estimation scheme is proposed. Simulation result show that the proposed algorithm has performance gains of 4.3dB in SNR compared to the conventional algorithms at the rate of 1% sync. failure probability for $2{\times}2$ MIMO-OFDM system and 18dB at 0.1% when maximum frequency offset exists. It also can be applied to $4{\times}4$ MIMO-OFDM system without any modification. Hence, it is very suitable for MIMO-OFDM WLAN systems using CSD preamble.

• Journal of IKEEE
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• v.24 no.1
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• pp.178-185
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• 2020

This paper proposes precise time synchronization-based synchronized sampling structure applied HW/SW platform for LAN-based protection of future digital substations. The integrated software of the proposed platform includes IEC 61850 protocol, IEEE 1588 precision time protocol and synchronized sampling structure. The proposed platform expected to provide a basis of an application of future distributed sensing data-based protection and control methods by providing synchronized measurement among IEDs. The implementation of the proposed HW/SW platform technique was performed using TMDXIDK572 multi-core/multi-processor evaluation module and its time synchronization performance and synchronized sampling function were confirmed through the performance tests.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.7
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• pp.669-676
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• 2015

In this paper, we described the simulation results of the phase offset performance of a clock in holdover mode which was normally operated in GPS Disciplined Oscillator (GPSDO). In the TIE model, we included the time error term caused by environmental temperature variation because one of the most important parameters of clock phase error is the frequency offset and drift caused by the variation of temperature. For the simulation, we employed Maximum Time Interval Error (MTIE) for the performance evaluation when the frequency offset and drift are estimated by using an Unbiased Finite Impulse Response (UFIR) filter with ladder algorithm. We assumed that the noise in the GPS measurement is white Gaussian with zero mean and 1 ns standard deviation, and temperature linearly varies with a slope of $1{^{\circ}C}$ per hour. From the simulation results, the followings were observed. First, with the estimation error of temperature of less than 3 % and the temperature compensation period of less than 900 seconds, the requirement of CDMA2000 phase synchronization under 10 us could be achieved for more than 40,000 seconds holdover time if we employ an OCXO (Oven Controlled Crystal Oscillator) clock. Second, in order to achieve the requirement of LTE-TDD under 1.5 us for more than 10,000 seconds holdover time, below 3 % estimation error and 500 seconds should be retained if a Rubidium clock is adopted.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.3
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• pp.622-629
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• 2004

Recently, as digital broadcasting and internet are spreaded out of the world, we can easily use informations with less restrictions of time and space. According to the current trends, concerns for the ways of representing multimedia data has been rapidly increased, and users demand the services with integrated document that takes not only simple text and image but also time varying audio-visual data. Therefore, in 1998, W3C presented an international standard, SMIL in order to solve multimedia object representation and synchronization problems. By using SMIL, various multimedia elements can be integrated as a multimedia document with proper view in a space and time. Using this SMIL document, we can create new internet radio broadcasting service that delivers not only audio data but also various text, image and video. In this paper, we describe on a SMIL document editor for the common users to be able to represent time varying multimedia data with special layout and synchronization of time and space.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.6
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• pp.1365-1376
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• 1997

In this paper, we designed real time mechanism control language and proposed execution time analysis technique. It was impossible to handle real-time mechanism control programs like programmable controller, numerical controller, distributed control system and robot controller with general purpose programming languages and operating systems because they have to process electric signals generated by thousands of sensors at the same at the same time and in real time. So we made it possible to predict plausibility of time constraint constructs of tiem constraint construct of a real time application program at compilation time by adding time constraint constructs and mechanism synchronization structure to conditional statement and iteration statement of a programming language and developing execution time analysis technique.

• Journal of KIISE:Computing Practices and Letters
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• v.9 no.4
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• pp.369-380
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• 2003

With the proliferation of a wireless support and the advances of mobile devices, there is a growing need of making it available for a wireless network as well. Low bandwidth of a wireless network is one of the major issues that should be considered for extending a synchronous collaboration system developed for a wired network to supuort a wireless network. We propose a priority-based view synchronization scheme, exploiting the relaxed synchronization. The proposed scheme leverages the fact that mobile users need not have the exactly same view as the users in a wired network since they usually have a limited screen size and thus focus only on part of a whole document. We evaluate the performance of a simple group editor with the propose scheme using ns -2. The performance results show that the proposed scheme keeps the message transmission delay low so that mobile users can have synchronous colloboration with wired users without signification delay. The proposed scheme is designed and implemented as a framework to support various kinds of realtime groupware applications, exploiting the existing groupware framework, Habanero. As a client program, we implemented a simple group text editor.

• Korean Journal of Animal Reproduction
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• v.11 no.3
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• pp.223-229
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• 1987

This study was carried out to investigate effects of superovulation and time of embryo recovery on ovarian response, recovery rate and developmental stage of embryo in donor and effects of methods of synchronization, number of corpus luteum (CL), stage of embryo and time of embryo transfer on ovarian response, conception rate and number of newborn in recipients which were transferred on 2.5, 3.5 and 4.5 days after synchronization. The results obtained are as follows; 1. The ovulation point of superovulated donor on 2.5, 3.5 and 4.5 days after copulation was 23.3, 35.3 and 23.3, respectively. The number of embryos recovered from the donors on 2.5, 3.5 and 4.5 days after copulation was 23.3, 25.8 and 19.8, respectively. The ovulation point and number of embryos recovered on 3.5 days were greater than those of 2.5 and 4.5 days. Among 232 embryos recovered on 3.5 days after copulation, 84 were blastocyst and 62 were hatching blastocyst. 2. The number of CL in recipients on 2.5, 3.5 and 4.5 days after synchronization was 3.2, 2.9 and 3.8 and showed no difference among the days. 3. When the number of CL was 0, 2-3, 4-6 and more than 7 the pregnancy raet of recipients was 0, 37.5, 66.7 and 75%, respectively. The pregnancy rate of recipients increased as the number of CL increased. 4. The pregnancy rate of transferred morula, blastocyst and hatching blastocyst was 32.0, 37.2 and 24.7%, respectively. The blastocyst nhowed highest pregnancy rate. 5. When the recipients were synchronized by HCG, the number of CL, unruptured follicle, hemorrhage, pregnancy rate and number of young were 5.5, 6.4, 3.3, 72.7% and 3.3, whereas that of GnRH were 2.3, 4.4, 2.8, 25.0% and 1.2, respectively. Recipients synchronized by HCG showed better results than GnRH. 6. When the embryos were collected on 2.5 days after copulation and transferred to the synchromized recipients, the pregnancy rate and the number of young born was 62.58% and 3.1, respectively. Those of 3.5 and 4.5 days after copulation was 57.1% and 1.3, and 37.5% and 1.6. The 2.5 days showed higher pregnancy rate and number of young born than 3.5 and 4.5 days.

• Journal of Embryo Transfer
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• v.27 no.4
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• pp.223-228
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• 2012

This study was designed to adopt two estrus synchronization protocols in zebu and crossbred heifers and their effects on pregnancy rate after timed artificial insemination (TAI). A number of 120 cyclic heifers were allotted for two different treatment groups and one control group. Heifers under protocol A were injected with GnRH at first day followed by a single dose of $PGF_{2{\alpha}}$ at Day 11 and injection of GnRH at the day of AI; and heifers belonged to protocol B were treated with GnRH, two $PGF_{2{\alpha}}$ injections at 11 days apart and injection of GnRH at AI. AI was done at fixed time (within 72~96 hours after $PGF_{2{\alpha}}$ injection) in both protocols and pregnancy was confirmed by rectal palpation on 80~120 days of post AI. In control group; local heifers were conceived higher (30%) proportion than that of crossbred heifers (25%; p<0.05). In protocol A, the local breed were conceived higher (38.9%) proportion compared with crossbred (25%; p<0.05). In protocol B, local breed heifers were conceived higher (38.9%) proportion compared with crossbred heifers (33.3%; p<0.05). The overall pregnancy rate in protocol A and protocol B was 33.3% and 36.6%, respectively. The proportion of pregnancy rate of local heifers (38.9%; Protocol A) was significant (p<0.05) in comparison with local heifers (30%) in control group (p<0.05). The overall pregnancy rate between pooled control group (28.3%) and treatment group (35%) was significantly (p<0.05) differ from each other's. Results of present study concluded that estrus synchronization followed by fixed time AI could be applied for higher pregnancy rate in zebu and crossbred heifers.