• Journal of The Korean Astronomical Society
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• v.55 no.6
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• pp.207-213
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• 2022

The Seoul Radio Astronomy Observatory (SRAO) operates a 6.1-meter radio telescope on the Gwanak campus of Seoul National University. We present the efforts to reform SRAO to a Very Long Baseline Interferometry (VLBI) station, motivated by recent achievements by millimeter interferometer networks such as Event Horizon Telescope, East Asia VLBI Network, and Korean VLBI Network (KVN). For this goal, we installed a receiver that had been used in the Combined Array for Research in Millimeter-wave Astronomy and a digital backend, including an H-maser clock. The existing hardware and software were also revised, which had been dedicated only to single-dish operations. After several years of preparations and test observations in 1 and 3-millimeter bands, a fringe was successfully detected toward 3C 84 in 86 GHz in June 2022 for a baseline between SRAO and KVN Ulsan station separated by 300 km. Thanks to the dual frequency operation of the receiver, the VLBI observations will soon be extended to the 1 mm band and verify the frequency phase referencing technique between 1 and 3-millimeter bands.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.4 no.2
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• pp.29-36
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• 2005

All-optical fiber-type $2{\times}32$ splitters for an Ethernet PON (passive optical network) were fabricated by using a FBT (fiber biconical tapered) process and the performance of the splitters was tested in upstream transmission of the EPON system. The $2{\times}32$ splitters was obtained by cascading $1{\times}4$ splitters fabricated by a conventional FBT process and showed -18 dB of insertion loss with 1.5 dB uniformity of output power at each channel and -0.1 dB of polarization dependent loss. The insertion loss variation was below 0.1 dB at the temperature range of $-40^{\circ}C\;to\;80^{\circ}C$. For upstream channel transmission test in the EPON system were a Zig board and a burst mode receiver. Zenko-made optical module was used for the burst mode receiver by adding functions of serializer/deserializer and clock data recovery, a Virtex II pro20 chipset and Vitesse VSC7123 were used in the Zig board for characterizing the burst mode and in the clock data recovery chipset, respectively. Startup acquisition lock time and data acquisition lock time were measured to be 670ns and 400ns, respectively, in the upstream channel transmission of the EPON system adapting the $2{\times}32$ splitter fabricated in this work.

• Smart Structures and Systems
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• v.18 no.5
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• pp.885-909
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• 2016

Advances in low-cost wireless sensing have made instrumentation of large civil infrastructure systems with dense arrays of wireless sensors possible. A critical issue with regard to effective use of the information harvested from these sensors is synchronized sensing. Although a number of synchronization methods have been developed, most provide only clock synchronization. Synchronized sensing requires not only clock synchronization among wireless nodes, but also synchronization of the data. Existing synchronization protocols are generally limited to networks of modest size in which all sensor nodes are within a limited distance from a central base station. The scale of civil infrastructure is often too large to be covered by a single wireless sensor network. Multiple independent networks have been installed, and post-facto synchronization schemes have been developed and applied with some success. In this paper, we present a new approach to achieving synchronized sensing among multiple networks using the Pulse-Per-Second signals from low-cost GPS receivers. The method is implemented and verified on the Imote2 sensor platform using TinyOS to achieve $50{\mu}s$ synchronization accuracy of the measured data for multiple networks. These results demonstrate that the proposed approach is highly-scalable, realizing precise synchronized sensing that is necessary for effective structural health monitoring.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1B
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• pp.86-97
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• 2009

RTLS is a system for automatically locating and tracking people and objects. The TDOA-based RTLS determines the location of the tag by calculating the time differences of a signal received from the tag. In TDOA-based RTLS, time synchronization is essential to calculate the time difference between readers. This paper presents a precision time synchronization method for TDOA-based RTLS over IEEE 802.15.4. In order to achieve precision time synchronization in IEEE 802.15.4 radio, we analyzed the error factors of delay and jitter. We also deal with the implementation of hardware assisted time stamping and the Kalman filtering method to minimize the error factors. In addition, this paper described the experiments and performance evaluation of the proposed precision time synchronization method in IEEE 802.15.4 radio. The results show that the nodes in a network can maintain their clocks to within 10 nanoseconds offset from the reference clock.

• Journal of Broadcast Engineering
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• v.16 no.5
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• pp.722-737
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• 2011

In this paper, we propose an estimation of network jitter that occurs when transmitting TCP packets containing MPEG-2 TS in progressive streaming service over wired or wireless Internet networks. Based on the estimated network jitter size, we can calculate required de-jitter buffering time to absorb the network jitter at the receiver side. For this purpose, by exploiting the PCR timestamp existing in the TS packet header, we create a new timestamp information that is marked in the optional field of TCP packet header to estimate the network jitter. By using the proposed de-jitter buffering scheme, it is possible to employ the conventional T-STD buffer model without any modification in the progressive streaming service over IP networks. The proposed method can be applicable to the recently developed international standard, MPEG DASH (dynamic adaptive streaming over HTTP) technology.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.1 no.2
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• pp.145-158
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• 1997

Method for synchronizing multimedia data is needed to support continuous transmission of multimedia data through a network in a bounded time and it also required for supporting continuous presentation of multimedia data with the required norminal playout rate in distributed network environments. This paper describes a new synchronization method for supporting delay-sensitive multimedia Presentation without degration of Quality of services of multimedia application. It mainly aims to support both intermedia and intermedia synchronization by absorbing network variations which may cause skew or jitter. In order to remove asynchonization problems, we make use of logical time system, dynamic buffer control method, and adjusting synchronization intervals based on the quality of services of a multimedia. It might be more suitable for working on distribute[1 multimedia systems where the network delay variation is changed from time to time and no global clock is supported. And it also can effectively reduce the amount of buffer requirements needed for transfering multimedia data between source and destination system by adjusting synchronization intervals with acceptable packet delay limits and packet loss rates.

• ETRI Journal
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• v.30 no.1
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• pp.129-140
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• 2008

In this paper, we propose a novel ant colony optimization (ACO)-based test scheduling method for testing network-on-chip (NoC)-based systems-on-chip (SoCs), on the assumption that the test platform, including specific methods and configurations such as test packet routing, generation, and absorption, is installed. The ACO metaheuristic model, inspired by the ant's foraging behavior, can autonomously find better results by exploring more solution space. The proposed method efficiently combines the rectangle packing method with ACO and improves the scheduling results by dynamically choosing the test-access-mechanism widths for cores and changing the testing orders. The power dissipation and variable test clock mode are also considered. Experimental results using ITC'02 benchmark circuits show that the proposed algorithm can efficiently reduce overall test time. Moreover, the computation time of the algorithm is less than a few seconds in most cases.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.279-282
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• 2000

As digital systems continue to use components with faster edge rates and clock speeds, transmission of the digital information in these systems approaches the microwave realm. At these speeds digital signal fidelity becomes both a critical success factor and design challenge. The noise sources in digital systems include the noise in power supply, ground and packaging media due to simultaneous switching of drivers, signal reflections and distortions on single and multiple transmission lines. This paper presents theory, case studies and design considerations of gigabit interconnection for network and communication systems. The case studies show HSPICE and Ampredictor simulations of alternate approaches. Various subjects including skin effect and dielectric losses, interconnect simulations and crosstalks of connector, affected signal discontinuity, are addressed.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2006.06a
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• pp.390-393
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• 2006

IEEE 802.11e 과 IEEE 802.11n에서 data의 높은 전송률을 구현하기 위해 Block Ack와 frame agegation 과 같은 새로운 mechanism이 논의 되고 있다. 이러한 mechanism은 각각의 MPDU processing 마다 짧은 응답시간을 요구한다. 본 논문에서는 위의 새로운 MAC을 지원하는 IEEE 802.11i를 위한 효율적인 CCMP 설계를 제안한다. 제안된 설계에서는 한 AES-CCM core에서 MIC calculation 과 정보 암호화가 128bit씩 순차적으로 수행되어지는 mode toggling 접근을 채택했다. 본 설계에서는 응답시간이 44 clock cycle의 짧은 짧은 시간으로 줄었다. 또한 하나의 AES-CCM core를 사용하고 낮은 주파수에서 수용할만한 data throughput과 응답시간을 얻었기 때문에 하드웨어적인 복잡성과 전력 소모를 줄일수 있었다.

• The Transactions of the Korea Information Processing Society
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• v.7 no.6
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• pp.1941-1948
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• 2000

Multistage interconnection networks (MINs) have been recognized as an efficient interconnection network for high-performance computer systems and also have been recently identified to be effective for a switching fabric of new communication structures - gigabit ethernet switch, terabit router, and ATM (asynchronous transfer mode). While lots of models analyzing the performance of MINs have been proposed, they are either inaccurate or, even if accurate, very complex for the analysis. In this paper, we propose an extremely simple mode for evaluating the multibuffered MIN with small clock cycles based on the approximation approach. Comprehensive computer simulation shows that the proposed model is very accurate in terms of the throughput and mean delay. Furthermore, it significantly reduces the computing overhead due to its simplicity.