• Proceedings of the Korea Information Processing Society Conference
• /
• 2007.11a
• /
• pp.917-920
• /
• 2007

무선 Ad-hoc 네트워크에서는 주로 IEEE 802.11 MAC 프로토콜을 이용한다. IEEE 802.11 MAC 프로토콜은 제어 메시지인 RTS-CTS를 통해서 채널 예약을 하고 데이터를 전송하는 방식으로 모든 통신에 Omni-directional 안테나를 이용하여 전송한다. 본 논문에서는 기존 IEEE 802.11 MAC 프로토콜보다 성능을 향상시키기 위해서 directional 안테나를 이용한 MAC 프로토콜을 사용한다. Directional 안테나를 사용한 MAC 프로토콜은 IEEE 802.11 MAC 프로토콜에 비해서 Spatial Reuse를 증가함으로서 채널 자원을 더욱 효율적으로 사용하는 것이 가능하다. 또한 Directional 안테나의 사용은 안테나의 지향성에 따른 안테나 이득 및 전송 범위의 증가 그리고 전송 범위를 Omni-directional 안테나와 동일하게 적용할 경우에는 저 전력 통신이 가능하다는 장점을 가지고 있다. 그러나 Directional 안테나의 사용은 IEEE 802.11 MAC보다 좋은 성능을 갖기는 하지만 새로운 문제들이 발생한다. 이러한 문제들로는 New Hidden Terminal, Deafness, Capture, 그리고 위치 인식에 관련된 문제들이 발생한다. 본 논문에서서 위에서 언급한 Directional 안테나의 이점과 그리고 문제점에 대해서 설명하고, 이러한 문제들 중에 Deafness 문제를 완화시킬 수 있는 방법을 제안한다. 그리고 QualNet 4.0을 이용한 시뮬레이션을 통해서 제안된 프로토콜의 성능을 평가한다.

• Korean Journal of Child Education & Care
• /
• v.17 no.4
• /
• pp.1-30
• /
• 2017

The purpose of this study is to investigate the awareness of daycare teachers by the nursery school operation performance of the National Competency Standards(NCS). For this purpose, 35 public and private daycare center, home daycare centers and corporation daycare center teachers were randomly sampled in Busan Metropolitan City. We conducted a questionnaire consisting of 230 sub-elements based on 45 sub-competency unit elements extracted from 12 areas of job ability of the national competence standards. Final questionnaires were collected from 117 questionnaires of 28 national daycare teachers, 30 private daycare teachers, 30 home daycare teachers, and 29 corporation daycare teachers. As a result, there was a difference in the awareness of importance among the four groups in all 12 performance capability units. For the 12 job performance units, the importance was recognized in the order of corporate daycare center, national daycare center, home daycare center, and private daycare center. Among them, "Establishment of Child Care Center Management Policy", "Construction of Child Care Service", "Child Care Activity Management", "Infant and Child Playing Guide", "Body and Art Activity Guidance", "Language, Nutritional guidance" there were no differences in the awareness of the importance of corporate daycare teachers and national daycare teachers, and there was no difference between national daycare teachers and home daycare teachers. However, there was a difference between corporate daycare teachers and home daycare teachers.. There is also a difference in the awareness of importance between home daycare teachers and private daycare teachers. In the remaining five job competence units, "Child Care Assessment", "Support for Infant and Toddler Development", "Cooperation with the Home and Community", "Child Care Management", and "Child Care Research", corporation daycare centers, national daycare centers. There was no statistically significant difference in the awareness of importance, but there was a significant difference from the private daycare teachers. Also this tendency was consistently observed in 45 sub-capacity unit elements.

• The KIPS Transactions:PartC
• /
• v.9C no.2
• /
• pp.293-296
• /
• 2002

UP Link is One of the commercial product which converts HTML to HDML convertor in order to show the internet www contents in the mobile environments. When UP browser accesses HTML pages, the agent in the UP Link controls the converter to change the HTML to the HDML, I-Mode, which is developed by NTT-Docomo of Japan, has many contents through the long and stable commercial service. Micro Explorer, which is developed by Stinger project, also has many additional function. In this paper, we designed and implemented WAP convertor which can accept C-HTML contents and mHTML contents. C-HTML format by I-Mode is a subset of HTML format, mHTML format by ME is similar to C-HTML, So the content provides can easily develop C-HTML contents compared with WAP and the other case. Since C-HTML, mHTML and WML are used under the mobile environment, the limited transmission capacity of one page is also similar. In order to make a match table. After that, we apply conversion algorithm on it. If we can not find matched element, we arrange some tags which only can be supported by WML to display in the best shape. By the result, we can convert over 90% contents.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.11 no.4
• /
• pp.1294-1300
• /
• 2010

In an environment where all nodes move, the sensor node receives anchor node's position information within communication radius and modifies the received anchor node's position information by one's traveled distance and direction in saving in one's memory, where if there at least 3, one's position is determined by performing localization through trilateration. The proposed localization mechanisms have been simulated in the Matlab. In an environment where certain distance is maintained and nodes move towards the same direction, the probability for the sensor node to meet at least 3 anchor nodes with absolute coordinates within 1 hub range is remote. Even if the sensor node has estimated its position with at least 3 beacon information, the angle ${\theta}$ error of accelerator and digital compass will continuously apply by the passage of time in enlarging the error tolerance and its estimated position not being relied. Dead reckoning technology is used as a supplementary position tracking navigation technology in places where GPS doesn't operate, where one's position can be estimated by knowing the distance and direction the node has traveled with acceleration sensor and digital compass. The localization algorithm to be explained is a localization technique that uses Dead reckoning where all nodes are loaded with omnidirectional antenna, and assumes that one's traveling distance and direction can be known with accelerator and digital compass. The simulation results show that our scheme performed better than other mechanisms (e.g. MCL, DV-distance).

• Journal of The Korean Association For Science Education
• /
• v.19 no.3
• /
• pp.400-408
• /
• 1999

This study investigated the effect of the grouping method in cooperative learning applied to chemistry concept learning. Two grouping methods used were the HML (High-Medium-Low) and the HL/MM (High-Low/Medium-Medium) ability grouping. Three classes (N = 136) at a high school in Seoul were randomly assigned to the control and the treatment groups. Before instruction. the test of attitude toward science instruction, the perception questionnaire of learning environment consisting of three subtests (participation, conflict, and competition), and the questionnaire of self-esteem were administered, and a mid-term examination score was obtained. These scores were used as covariates. After instruction, the three tests administered before instruction and the conceptions test were administered. Two-way ANCOVA results revealed that there was a significant interaction between the treatment and the level of previous achievement. The low-level students in the HL/MM cooperative group performed better than those in the other groups. The cooperative groups, regardless of the grouping methods, exhibited more positive perception than the control group at participation subtest of the perception questionnaire of learning environment.

• Journal of The Korean Association For Science Education
• /
• v.36 no.4
• /
• pp.519-526
• /
• 2016

The purpose of this study is to investigate the influences of small group learning using smart devices in science classes on students' achievement, learning motivation, attitude toward science lessons, and perception of small group learning using smart devices. Four 11th-grade classes (N=133) at a coed high school in Seoul were randomly assigned to a control group and a treatment group. The intervention of small group learning using smart devices emphasized collaborative writing on activity sheet. The students were taught about acid, base, and neutralization reaction for six class periods. After the instructions, an achievement test, the learning motivation test, the attitude toward science lessons test, and a questionnaire on the perception of small group learning using smart devices were administered. Two-way ANCOVA results revealed that there was a statistically significant interaction effect by their previous chemistry achievement in the achievement test scores. Only low-level students in small group learning using smart devices significantly improved their achievement probably by having the opportunities to get help from high-level students. The adjusted means of the treatment group were significantly higher than those of the control group in learning motivation and attitude toward science lessons. Students' perceptions of small group learning using smart devices tended to be positive. Educational implications of this study are discussed.

• KIPS Transactions on Computer and Communication Systems
• /
• v.2 no.10
• /
• pp.427-436
• /
• 2013

In this paper, a method of moving path control of an automatic guided vehicle in an indoor environment through recognition of marker images using vision sensors is presented. The existing AGV moving control system using infrared-ray sensors and landmarks have faced at two critical problems. Since there are many windows in a crematorium, they are going to let in too much sunlight in the main hall which is the moving area of AGVs. Sunlight affects the correct recognition of landmarks due to refraction and/or reflection of sunlight. The second one is that a crematorium has a narrow indoor environment compared to typical industrial fields. Particularly when an AVG changes its direction to enter the designated furnace the information provided by guided sensors cannot be utilized to estimate its location because the rotating space is too narrow to get them. To resolve the occurrences of such circumstances that cannot access sensing data in a WSN environment, a relative distance from marker to an AGV will be used as fingerprinting used for location estimation. Compared to the existing fingerprinting method which uses RSS, our proposed method may result in a higher reliable estimation of location. Our experimental results show that the proposed method proves the correctness and applicability. In addition, our proposed approach will be applied to the AGV system in the crematorium so that it can transport a dead body safely from the loading place to its rightful destination.

• Journal of Internet Computing and Services
• /
• v.10 no.6
• /
• pp.51-79
• /
• 2009

Today the service industry is growing, and differentiated services for marketing and service quality is emerging as a serious problem. Until now, the WebCam is used for observation, and the negative aspects, such as from a human rights issue has become. Discipline and Punish is not to use a webcam to customer satisfaction research is needed. Therefore, wireless monitoring in WebCam service quality of the service reconfiguration and service quality factors for the configuration of the customer's preference regarding how research was recognized. Configuration of the service quality factors WebCam service customer satisfaction and customer loyalty was to identify factors that affect. These services to study the correlation between the quality variables WebCam provides wireless monitoring services for the preschool and children, a survey of the house. Configuring a wireless monitoring service quality in order to research the factors WebCam video quality and transmission speed, mobility and portability, convenience, visibility, reliability, and the interaction of the castle set. Severely and video quality and transmission speed, visibility, reliability, customer satisfaction, the interaction factors are said. Inclination to participate in social issues, innovation, digital devices that use a skilled, depending on the difference in the service quality has been confirmed. However, the age and quality of service awareness and job types showed a low correlation, and the marketing of these results will be discussed and how that can be used.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.21 no.5
• /
• pp.71-82
• /
• 2011

The RFID system provides undeniable advantages so that it is used for various application. However recent RFID system is vulnerable to some attacks as eavesdropping, replay attack, message hijacking, and tag tampering, because the messages are transmitted through the wireless channel and the tags are cheap. Above attacks cause the tag and reader impersonation, denial of service by invalidating tag, and the location tracking concerning bearer of tags, A lot of RFID authentication protocol bas been proposed to solve the vulnerability. Since Weis, Sanna, Rivest, and Engel, proposed the bash-based RFID authentication protocol, many researchers have improved hash-based authentication protocol and recent bash-based authentication protocols provide security and desirable privacy. However, it remains open problem to reduce the tag identification time as long as privacy and security are still guaranteed. Here we propose a new protocol in which the tags generate the message depending on the state of previous communitions between tag and reader. In consequence, our protocol allows a server to identify a tag in a reasonable amount of time while ensuring security and privacy, To be specific, we reduced the time for the server to identify a tag when the last session finished abnormally by at least 50% compared with other bash-based schemes that ensure levels of security and privacy similar to ours.

• Journal of the Korean Chemical Society
• /
• v.62 no.2
• /
• pp.124-136
• /
• 2018

In this study, we applied the flipped-classroom to the general chemistry experiment lecture of the domestic university with strong teacher-led, and explored the effects and possibilities of the course. For this purpose, 30 students who were enrolled in the Science Education Department of the College of Education in the metropolitan area were randomly assigned to two groups, namely, the flipped-classroom group and the traditional class group. Then, we developed a general chemistry experiment lessons based on the flipped-classroom along with visual materials and we applied the lessons for 15 weeks. After all the classes, we conducted a survey to see the students' perception of the general chemistry experiment lecture by flipped classroom. As a result of analysis, the students of the flipped-classroom group were more positive than the students of the traditional class group in terms of the usefulness of the class activity, the importance of each activity element for the successful learning, the learning level, and the intention for another lesson. As a result of analyzing students' perceptions in terms of general chemical experiment activities such as conducting experiments or writing reports and understanding the contents of experiments, the average score of the flippedclassroom group was higher than the traditional class group, and the main cause of this result was the video material provided by prior learning activities. In addition, as a result of analyzing students' perceptions in terms of interactions and self-directed learning in class, the average score of the flipped-classroom group was generally higher than the traditional class group. In particular, students' interactions and self-directed learning were statistically significant differences between the two groups. And the students' perception of video material was very positive, and it was analyzed that the video that the instructor directly explained experiment theory and method was the most favorite videos of students. We discussed educational implications of these findings.