Hyuntae Cho

Bio: Hyuntae Cho is an academic researcher from KAIST. The author has contributed to research in topics: Synchronization & Clock synchronization. The author has an hindex of 12, co-authored 50 publications receiving 469 citations. Previous affiliations of Hyuntae Cho include Pusan National University.

Precision Time Synchronization Using IEEE 1588 for Wireless Sensor Networks

Abstract: Wireless sensor networks are evolving from relatively undemanding applications to applications which have stronger requirements. The coordination of distributed entities and events requires time synchronization. Although a number of methods have been studied for WSNs, some applications require high precision time synchronization. Precision time synchronization enables a variety of extensions of applications. The IEEE 1588 precision time protocol (PTP) provides a standard method to synchronize devices in a network with sub-microsecond precision. This paper deals with precision time synchronization using IEEE 1588 over wireless sensor networks. Precision time synchronization using IEEE 1588 provides compatibility between heterogeneous systems in WSNs. This paper also presents experiments and performance evaluation of precision time synchronization in WSNs. Our result established a method for nodes in a network to maintain their clocks to within a 200 nanosecond offset from the reference clock of a master node.

Implementation of a precision time protocol over low rate wireless personal area networks

Abstract: Time synchronization is essential for a number of network applications. As the era of ubiquitous computing is ushered in, high precision time synchronization of nodes in wireless networks is required. High precision time synchronization can enable a variety of extensions of applications. This paper includes the design and implementation of the precision time protocol over low rate wireless personal area networks (LR-WPANpsilas). To achieve high precision in LR-WPANpsilas, we analyze the factors of latency and jitter in wireless environments, and we aim to minimize these factors. In addition, this paper presents experiments and the performance evaluation of the precision time protocol in LR-WPANpsilas. The result is that we established for nodes in a network to maintain their clocks to within a 50 nanosecond offset from the reference clock.

Large scale active RFID system utilizing ZigBee networks

Abstract: As the era of the ubiquitous computing is ushered in, consumers have been primed for a variety of automation applications. Active RFIDs can be used for a number of automation applications because it may also have other sensors to extend its applications. An active RFID instinctively focuses on a long communication range. Nevertheless, active RFIDs cannot be applied to a large-scale area due to their limited radio communication and obstacles. This paper introduces a large-scale active RFID system based on multi-hop deployment utilizing dual radio frequency to overcome radio shadow areas that do not reach signals from the RFID reader. The proposed system consists of multiple RFID readers deployed in an ad hoc pattern. It uses a multihop collection scheme utilizing ZigBee networks to extend the coverage of the RFID reader and collect RFID tags outside its communication range. This paper also includes an experiment evaluating performance of the proposed method, using an implemented RFID system that complies with the standard for 433 MHz active RFIDs based on ISO/IEC 18000-7.

Design and implementation of an active RFID system platform

Abstract: An active RFID system has the active tag that incorporates an internal battery providing a robust, long-range transmission signal. Typical application using the active RFID is the identification and the position tracking of warehouse inventory-item and freight container. This paper presents the design and implementation of an active RFID system platform which complies with the ISO/TEC 18000-7 standard. Our system design focus on three parts: 1) the standard compliance with the ISO/TEC 18000-7, 2) the energy saving mechanism to maintain the longevity of tags as long as possible, and 3) the high identification rate in the presence of multiple tags. We describe the detailed design of the system and the commercial off-the-shelf (COTS) implementation. The performance evaluation of the system is also included.

Practical localization system for consumer devices using zigbee networks

Abstract: As the era of ubiquitous computing dawns, there is a growing need for a reliable, efficient positioning and tracking system. A localization system involves ongoing tracking of the location of assets and personnel. This paper presents a practical localization system for consumer devices on Zigbee networks. The proposed system is based on time-difference-of-arrival (TDOA). Localization based on TDOA involves estimating the location of the device by calculating the time-difference-of-arrival of the signal received from a device. In order to calculate the time difference of the signal, TDOA-based methods require precision time measurements of the signal, and reader time synchronization accurate to within a few nanoseconds. We also propose a precise time stamping unit, which enables the system to determine the arrival time of the radio signal, and a precision time synchronization protocol, which enables readers to have a reference clock. In addition, this paper includes an experimental performance evaluation of the localization system. The performance shows that the localization system has a DRMS of approximately two meters in a harsh environment.

[서평]「Applied Cryptography」

Abstract: The objective of this paper is to give a comprehensive introduction to applied cryptography with an engineer or computer scientist in mind. The emphasis is on the knowledge needed to create practical systems which supports integrity, confidentiality, or authenticity. Topics covered includes an introduction to the concepts in cryptography, attacks against cryptographic systems, key use and handling, random bit generation, encryption modes, and message authentication codes. Recommendations on algorithms and further reading is given in the end of the paper. This paper should make the reader able to build, understand and evaluate system descriptions and designs based on the cryptographic components described in the paper.

Population and Housing Census

Abstract: The questionnaires from the field were received, checked and stored by the data processing personnel. They checked: 1. The completeness of the questionnaires 2. The correct bubbling 3. The correct number of questionnaires per household, if total males + total females > 8 as the questionnaire ONLY accommodated maximum of 8 household members. 4. The reference number appears in all the 10 pages of the questionnaires.

Color-wave : An anticollision algorithm for the reader collision problem

Abstract: We present the Colorwave algorithm, a simple, distributed, on-line algorithm for the reader collision problem in radio frequency identification (RFID) systems. RFID systems are increasingly being used in applications, such as those experienced in supply chain management, which require RFID readers to operate in close proximity to one another. Readers physically located near one another may interfere with one another's operation. Such reader collisions must be minimized to ensure the correct operation of the RFID system. The Colorwave algorithm yields on-line solutions that are near the optimal static solutions. The dynamic nature of the algorithm enables the RFID system to automatically adapt to changes in the system and in the operating environment of the system.

Device for optically scanning and measuring an environment

Abstract: A device for optically scanning and measuring an environment is provided. The device includes a movable scanner having at least one first projector for producing at least one uncoded first pattern on an object in the environment. The scanner includes at least one camera for recording images of the object provided with the pattern and a controller coupled to the first projector and the camera. The device further includes at least one second projector which projects a stationary uncoded second pattern on the object while the scanner is moved. Wherein the controller has a processor configured to determine a set of three-dimensional coordinates of points on a surface of the object from a set of images acquired by the camera based at least in part on the first pattern. The controller is further configured to register the set of images relative based in part on the stationary second pattern.

Advances in Smart Environment Monitoring Systems Using IoT and Sensors

Abstract: Air quality, water pollution, and radiation pollution are major factors that pose genuine challenges in the environment. Suitable monitoring is necessary so that the world can achieve sustainable growth, by maintaining a healthy society. In recent years, the environment monitoring has turned into a smart environment monitoring (SEM) system, with the advances in the internet of things (IoT) and the development of modern sensors. Under this scenario, the present manuscript aims to accomplish a critical review of noteworthy contributions and research studies on SEM, that involve monitoring of air quality, water quality, radiation pollution, and agriculture systems. The review is divided on the basis of the purposes where SEM methods are applied, and then each purpose is further analyzed in terms of the sensors used, machine learning techniques involved, and classification methods used. The detailed analysis follows the extensive review which has suggested major recommendations and impacts of SEM research on the basis of discussion results and research trends analyzed. The authors have critically studied how the advances in sensor technology, IoT and machine learning methods make environment monitoring a truly smart monitoring system. Finally, the framework of robust methods of machine learning; denoising methods and development of suitable standards for wireless sensor networks (WSNs), has been suggested.