• ETRI Journal
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• v.31 no.4
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• pp.466-468
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• 2009

In this letter, we propose a one-way ranging algorithm that is based on wireless synchronization with measured timestamps and clock frequency offsets. In our proposed algorithm, an active mobile node initiates a ranging procedure by transmitting a ranging frame, and the anchor nodes report their timestamps for the received ranging frame to a reference anchor node. The synchronization of a pair of nodes is provided with instantaneous time information, and the corresponding difference of distances can be calculated.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.2
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• pp.125-130
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• 2013

Compared to OWR (One-Way Ranging) method that requires precise network time synchronization, TWR (Two-Way Ranging) method has advantages in building an indoor WPAN (Wireless Personal Area Network) location system with lower cost. However, clock offsets of nodes in WPAN system should be eliminated or compensated to improve location accuracy of the TWR method. Because conventional clock offset elimination methods requires multiple TWR transactions to reduce clock offset, they produce network traffic burden instead. This paper presents a clock offset estimation method that can reduce clock offset error with a single TWR transaction. After relative clock offsets of sensor nodes are estimated, clock offsets of mobile tags are estimated using a single TWR communication. Simulation results show that location accuracy of the proposed method is almost similar to the conventional clock offset elimination method, while its network traffic is about a half of the conventional method.

• Korean Journal of Child Studies
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• v.8 no.1
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• pp.65-82
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• 1987

The purpose of the present research was to study mothers' perceptions about their children' cognitive abilities and the relations between such perceptions and the children's cognitive level. The subjects of this study were 60 children (mean age: 6 years 1 month: age range = 5;8 to 6;7) and their mothers. Each child responded to 18 tasks drawn from the Kodae-Binet IQ test. Subsequently, the mothers were asked 4 questions: an estimate of her child's success or failure on the tasks, a rating of the certainty of her judgment, an estimate of the age of mastery on each task both for her owr child and children in general. The data of the present study were analyzed with the 3-way ANOVA (sex x birth order x mother's education level), t-test, and Pearson correlation coefficient. Significant differences were found in (1) mothers' accuracy of their children's cognitive abilities according to children's birth order, (2) mothers' accuracy, overestimation, and certainty according to the level of difficulty of each task, and (3) mothers' estimate of age at mastery according to the level of each task. Furthermore, there were positive correlations between accurate predictions by the mother and correct answers by the child and between overestimations by the mother and correct answers by the child.

• IEMEK Journal of Embedded Systems and Applications
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• v.5 no.4
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• pp.234-242
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• 2010

Two-way ranging methods such as TWR and SDS-TWR have been considered for many ranging systems because these methods are useful in the absence of synchronization. To estimate the location of a mobile node, complicated ranging procedures consisting of ranging frames between an anchor node and the mobile node are performed. Supporting multiple mobile nodes such as a few hundreds or thousands and several anchor nodes, the ranging procedures have the fatal disadvantage of processing delay and inefficient traffic bandwidth. On the other hand, the one-way ranging method is simple and fast, but susceptible to network synchronization. In this paper, we propose a method to modify asynchronous ranging equations to establish exact frequency or frequency offset, a method to estimate frequencies or frequency offsets, and a method to establish post-facto synchronization with anchor nodes. The synchronization for a node pair is adapted using instantaneous time information and corresponding difference of distances can be determined. We evaluate the performance of TWR, SDS-TWR and proposed ranging algorithms.

• The Journal of Korea Robotics Society
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• v.12 no.3
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• pp.350-355
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• 2017

UWB (Ultra Wide Band) refers to a system with a bandwidth of over 500 MHz or a bandwidth of 20% of the center frequency. It is robust against channel fading and has a wide signal bandwidth. Using the IR-UWB based ranging system, it is possible to obtain decimeter-level ranging accuracy. Furthermore, IR-UWB system enables acquisition over glass or cement with high resolution. In recent years, IR-UWB-based ranging chipsets have become cheap and popular, and it has become possible to implement positioning systems of several tens of centimeters. The system can be configured as one-way ranging (OWR) positioning system for fast ranging and TWR (two-way ranging) positioning system for cheap and robust ranging. On the other hand, the ranging based positioning system has a limitation on the number of terminals for localization because it takes time to perform a communication procedure to perform ranging. To overcome this problem, code multiplexing and channel multiplexing are performed. However, errors occur in measurement due to interference between channels and code, multipath, and so on. The measurement filtering is used to reduce the measurement error, but more fundamentally, techniques for removing these measurements should be studied. First, the TWR based positioning was analyzed from a stochastic point of view and the effects of outlier measurements were summarized. The positioning algorithm for analytically identifying and removing single outlier is summarized and extended to three dimensions. Through the simulation, we have verified the algorithm to detect and remove single outliers.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.609-613
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• 2003

The confinement of a storage system to accommodate spent fuel and radioactive material must be designed and estimated so that the storage system is safe during a storage period. The confinement can be estimated by calculation of the allowable leakage rate in compliance with ANSI Nl4.5 or ISO 12807. Accordingly, the allowable leakage rate was estimated in compliance with ISO 12807 in the case of storage of 24 PWR spent fuels and 24-conditioned spent fuels. In the case of the 24 PWR spent fuel assemblies, the allowable leakage rate was estimated as $7.43{\times}10_{-11}m_3/s$, in the case of the 24 conditioned spent fuel assemblies, the allowable leakage rate was estimated as $1.80{\times}10_{-10}m_3/s$. Therefore, the confinement condition in the storage of the conditioned spent fuel is easier than that for the storage of the PWR spent fuel.

• Journal of Gastric Cancer
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• v.8 no.4
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• pp.225-231
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• 2008

Purpose: Laparoscopic gastric resection (LGR) is increasingly being used instead of open gastric resection (OGR) as the standard surgical treatment for gastric submucosal tumors. Yet there are few reports on which technique shows better postoperative outcomes. This study was performed to compare these two treatment modalities for gastric submucosal tumors by evaluating the postoperative outcomes. We also provide an analysis of the learning curve for LGR. Materials and Methods: Between 2003.4 and 2008.8, 103 patients with a gastric submucosal tumor underwent either LGR (N=78) or OGR (n=25). A retrospective review was performed on a prospectively obtained database of 103 patients. We reviewed the data with regard to the operative time, the blood loss during the operation, the time to the first soft diet, the postoperative hospital stay, the tumor size and the tumor location. Results: The clinicopatholgic and tumor characteristics of the patients were similar for both groups. There was no open conversion in the LGR group. The mean operation time and the bleeding loss were not different between the LGR group and the OWR group. The time to first soft diet (3.27 vs. 6.16 days, P<0.001) and the length of the postoperative hospital stay (7.37 vs. 8.88 days, P=0.002) were shorter in the LGR group compared to the OGR group. The tumor size was bigger in the OGR group than that in the LGR group (6.44 vs. 3.65 cm, P<0.001). When performing laparoscopic gastric resection of gastric SMT, the surgeon was able to decrease the operation time and bleeding loss with gaining more experience. We separated the total cases into 3 periods to compare the operation time, the bleeding losses and the complications. The third period showed the shortest operation time, the least bleeding loss and the fewest complications. Conclusion: LGR for treating a gastric submucosal tumor was superior to OGR in terms of the postoperative outcomes. An operator needs some experience to perform a complete laparoscopic gastric resection. Laparoscopic resection could be considered the first-line treatment for gastric submucosal tumors.