Yunju Baek

Bio: Yunju Baek is an academic researcher from Pusan National University. The author has contributed to research in topics: Real-time locating system & Synchronization. The author has an hindex of 15, co-authored 84 publications receiving 825 citations. Previous affiliations of Yunju Baek include KAIST.

RFID-Based Real-Time Locating System for Construction Safety Management

Abstract: This paper presents the development of a radiofrequency identification (RFID)–based real-time locating system (RTLS) for safety management. The particular focus of this paper is the creation of the RTLS, which provides accurate and robust localization performance in construction sites where it is otherwise very difficult to maintain signal availability because of many (moving) obstacles. Adopted were the Time of arrival method as a localization method, the Chirp spread spectrum as a wireless networking technology, and the Assistant Tag as a way to maintain enough signal availability for effective communication. In addition, the developed RTLS uses RFID to retain the latter’s benefits (e.g., data storage, transfer capability, relatively inexpensive installation cost). To demonstrate the RTLS’s localization performance, two case studies have been conducted; the results show great potential for use in improving construction site safety management.

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.

Re-ranking algorithm using post-retrieval clustering for content-based image retrieval

Abstract: In this paper, we propose a re-ranking algorithm using post-retrieval clustering for content-based image retrieval (CBIR). In conventional CBIR systems, it is often observed that images visually dissimilar to a query image are ranked high in retrieval results. To remedy this problem, we utilize the similarity relationship of the retrieved results via post-retrieval clustering. In the first step of our method, images are retrieved using visual features such as color histogram. Next, the retrieved images are analyzed using hierarchical agglomerative clustering methods (HACM) and the rank of the results is adjusted according to the distance of a cluster from a query. In addition, we analyze the effects of clustering methods, querycluster similarity functions, and weighting factors in the proposed method. We conducted a number of experiments using several clustering methods and cluster parameters. Experimental results show that the proposed method achieves an improvement of retrieval effectiveness of over 10% on average in the average normalized modified retrieval rank (ANMRR) measure.

An efficient block-matching criterion for motion estimation and its VLSI implementation

Abstract: The block-matching motion estimation is the most popular technique for motion compensated coding of image sequence. Due to the intensive computational requirement to perform motion estimation (ME) in real-time, application specific VLSI implementation of the ME is indispensable. We present a novel block-matching criterion for motion estimation called reduced bits mean absolute difference (RBMAD). By comparison with conventional schemes, our scheme reduces hardware requirement and increases the speed of computation in VLSI chip with acceptable video performance. We describe in detail the video performances of proposed criterion and conventional ones. We also show our VLSI implementation using the proposed scheme to compare the hardware requirement and operating speed with conventional ones. It is found that RBMAD using 4 bits has reasonable video performance with 57% less VLSI area and 34% faster, thus it is suitable for low cost applications of video coding.

Digital Watermarking

Abstract: Digital watermarking is a key ingredient to copyright protection. It provides a solution to illegal copying of digital material and has many other useful applications such as broadcast monitoring and the recording of electronic transactions. Now, for the first time, there is a book that focuses exclusively on this exciting technology. Digital Watermarking covers the crucial research findings in the field: it explains the principles underlying digital watermarking technologies, describes the requirements that have given rise to them, and discusses the diverse ends to which these technologies are being applied. As a result, additional groundwork is laid for future developments in this field, helping the reader understand and anticipate new approaches and applications.

[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.

Computer and Robot Vision

Abstract: Computer and Robot Vision Vol. 1, by R.M. Haralick and Linda G. Shapiro, Addison-Wesley, 1992, ISBN 0-201-10887-1.

VisualRank: Applying PageRank to Large-Scale Image Search

Abstract: Because of the relative ease in understanding and processing text, commercial image-search systems often rely on techniques that are largely indistinguishable from text search. Recently, academic studies have demonstrated the effectiveness of employing image-based features to provide either alternative or additional signals to use in this process. However, it remains uncertain whether such techniques will generalize to a large number of popular Web queries and whether the potential improvement to search quality warrants the additional computational cost. In this work, we cast the image-ranking problem into the task of identifying "authority" nodes on an inferred visual similarity graph and propose VisualRank to analyze the visual link structures among images. The images found to be "authorities" are chosen as those that answer the image-queries well. To understand the performance of such an approach in a real system, we conducted a series of large-scale experiments based on the task of retrieving images for 2,000 of the most popular products queries. Our experimental results show significant improvement, in terms of user satisfaction and relevancy, in comparison to the most recent Google image search results. Maintaining modest computational cost is vital to ensuring that this procedure can be used in practice; we describe the techniques required to make this system practical for large-scale deployment in commercial search engines.