• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.8 no.6
• /
• pp.1881-1900
• /
• 2014

Since 802.11 wireless LANs are so widely used, it has become common for numerous access points (APs) to overlap in a region, where most of those APs are managed individually without any coordinated control. This pattern of wireless LAN usage is called the private OBSS (Overlapping Basic Service Set) environment in this paper. Due to frame collisions across BSSs, each BSS in the private OBSS environment suffers severe performance degradation. This study approaches the problem from the perspective of congestion control rather than noise or collision resolution. The retry limit, one of the 802.11 attributes, could be used for traffic control in conjunction with TCP. Reducing the retry limit causes early discard of a frame, and it has a similar effect of random early drops at a router, well known in the research area of congestion control. It makes the shared link less crowded with frames, and then the benefit of fewer collisions surpasses the penalty of less strict error recovery. As a result, the network-wide performance improves and so does the performance of each BSS eventually. Reducing the retry limit also has positive effects of merging TCP ACKs and reducing HOL-like blocking time at the AP. Extensive experiments have validated the idea that in the OBSS environment, reducing the retry limit provides better performance, which is contrary to the common wisdom. Since our strategy is basically to sacrifice error recovery for congestion control, it could yield side-effects in an environment where the cost of error recovery is high. Therefore, to be useful in general network and traffic environments, adaptability is required. To prove the feasibility of the adaptive scheme, a simple method to dynamically adjust the value of the retry limit has been proposed. Experiments have shown that this approach could provide comparable performance in unfriendly environments.

• Journal of the Korean Society of Radiology
• /
• v.17 no.1
• /
• pp.47-52
• /
• 2023

In whole spine radiography using the stitching technique, overlapping parts occur in the process of synthesizing the three segmented images, so some anatomical structures may be repeatedly exposed, and it has been thought that the dose increases as the scan range increases. However, in the whole spine radiography using the stitching technique in this study, under the condition that the stitching range is taken in the same three splits, the overlapping area decreases as the stitching range increases, so in the case of breasts included in the overlapping range, the dose value decreased by almost half as the stitching range increased from 90 cm to 105 cm. During spinal full-length radiological examination using the stitching method, an appropriately long stitching range could be set to reduce the exposure dose of the breast.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.18 no.5
• /
• pp.685-691
• /
• 2008

The selection of classification boundaries in fuzzy rule- based classification systems is an important and difficult problem. So various methods based on learning processes such as neural network, genetic algorithm, and so on have been proposed for it. In a previous study, we pointed out the limitation of the methods and discussed a method for fuzzy partitioning in the overlapped region on feature space in order to overcome the time-consuming when the additional parameters for tuning fuzzy membership functions are necessary. In this paper, we propose a method to determine three types of classification boundaries(i.e., non-overlapping, overlapping, and a boundary point) on the basis of statistical information of the given dataset without learning by extending the method described in the study. Finally, we show the effectiveness of the proposed method through experimental results applied to pattern classification problems using the modified IRIS and standard IRIS datasets.

• Journal of KIISE:Software and Applications
• /
• v.36 no.10
• /
• pp.861-873
• /
• 2009

There are many reasons that fail to get appropriate information in information retrieval. Allomorph is one of the reasons for search failure due to keyword mismatch. This research proposes a method to construct alternative word candidates automatically in order to minimize search failure due to keyword mismatch. Assuming that two words have similar meaning if they have similar co-occurrence words, the proposed method uses the concept of concentration, association word set, cosine similarity between association word sets and a filtering technique using confidence. Performance of the proposed method is evaluated using a manually extracted alternative list. Evaluation results show that the proposed method outperforms the context window overlapping in precision and recall.

• Journal of the Korean Geotechnical Society
• /
• v.20 no.3
• /
• pp.97-106
• /
• 2004

In case of tunnel construction with a shallow soil cover in cohesionless soils or highly weathered rocks, reinforcement measures are required for a tunnel stability during the tunnel construction. Recent developments show that the use of Umbrella Arch Method(UAM) as tunnel reinforcement and water cut-off in domestic projects has increased. Unfortunately, guidelines for the design and construction of UAM have not been established, only empirical designs and applications in tunnel construction have been performed so far. In this study, behaviour of the steel pipes installed on the tunnel roof was analyzed through the monitoring of bending and axial stresses of the pipes with the advance of the tunnel face. The monitoring results were used in the establishment of the loading mechanism around the pipe. This paper suggests, the guidelines used in the determination of the total length, overlapping length and lateral spacing of the reinforcing pipes obtained from the established loading mechanism.

• Journal of the Korea Fashion and Costume Design Association
• /
• v.25 no.1
• /
• pp.133-152
• /
• 2023

The purpose of this study is to provide basic data to assist students and designers in the fashion industry by examining the trend of designing women's wear using the SCAMPER method. In the research, five SCAMPER methods for fashion design were classified based on the previous studies. From 2018 S/S to 2022 F/W, data from 3,512 photographs were collected and checked for overlapping and were then classified by SCAMPER method. Data analysis was performed using SPSS 26 for frequency analysis. As a result, the most common application of the SCAMPER method was in 2022. First, the most used SCAMPER method for design was the "modify" method, changing details into various forms. The second method was the "adapt" method in which parts of the design or details were added and connected. The third mehtod was the "magnify" method of enlarging the length of the jacket. The fourth method was the "eliminate" method, removing parts of the jacket bodice, collar, or sleeves.

• The Transactions of the Korean Institute of Electrical Engineers D
• /
• v.50 no.12
• /
• pp.590-596
• /
• 2001

The pre-emphasis is an essential process for speech signal processing. Widely used two methods are the typical method using a fixed value near unity and te optimal method using the autocorrelation ratio of the signal. This study proposes a new pre-emphasis method using the short-term energy difference of speech signal, which can effectively compensate the glottal source characteristics and lip radiation characteristics. Using the proposed pre-emphasis, speech analysis, such as spectrum estimation, formant detection, is performed and the results are compared with those of the conventional two pre-emphasis methods. The speech analysis with 5 single vowels showed that the proposed method enhanced the spectral shapes and gave nearly constant formant frequencies and could escape the overlapping of adjacent two formants. comparison with FFT spectra had verified the above results and showed the accuracy of the proposed method. The computational complexity of the proposed method reduced to about 50% of the optimal method.

• International conference on construction engineering and project management
• /
• 2011.02a
• /
• pp.445-452
• /
• 2011

The schedule hierarchy in construction project is generally composed of three levels. The highest level is a milestone schedule and represented by Bar Chart format. The middle level is an integrated project schedule (IPS) and represented by CPM (Critical Path Method) format. The lowest level is a detail working schedule and usually represented by Bar Chart. The traditional scheduling techniques such as ADM (Arrow Diagramming Method) or PDM (Precedence Diagramming Method) cannot represent all kinds of schedule within schedule hierarchy as identical schedule format. However, the BDM (Beeline Diagramming Method) technique can represent all kinds of schedule within schedule hierarchy as identical CPM format. This paper describes the basic concept, principle, interpretation methods, and schedule computation methods of the BDM as a new networking technique that can represent all kinds of overlapping relationships between activities, and then presents an example of representing three level's schedules within schedule hierarchy by the BDM technique.

• Journal of the Korean Institute of Educational Facilities
• /
• v.19 no.2
• /
• pp.41-50
• /
• 2012

This study aims to analyze chlidcare philosophy and the architectural characteristics of communal childcare cooperative nurseries(parent cooperative childcare facilities), and also to examine their mutual relationship. The communal childcare cooperative is an ideal childcare method to break away from employee-supported childcare system and cooperatively solve childcare problems in the family community system. The child-rearing philosophy of the communal childcare can bring spontaneous and creative development amidst 'daily life' and 'play' by switching from knowledge and skill-oriented education and puts an emphasis on physical environments in child's growth. The features of architecture related the childcare philosophy derived from this study are as follows: the way of participation and self-help, the extension of spatial scope and focuses on outside space, architecture of house-like residence rather than educational facility, spatial 'overlapping' focusing on transitional space and multi-purpose space rather than spatial partitions, the pursuit of creativity through play is realized in the incompletion and unspecification of space evolving over time.

• 제어로봇시스템학회:학술대회논문집
• /
• 2003.10a
• /
• pp.2519-2523
• /
• 2003

Ultrasonic sensors are widely used in mobile robot applications to recognize external environments, because they are cheap, easy to use, and robust under varying lighting conditions. In most cases, a single ultrasonic sensor is used to measure the distance to an object based on time-of-flight (TOF) information, whereas multiple sensors are used to recognize the shape of an object, such as a corner, plane, or edge. However, the conventional sequential driving technique involves a long measurement time. This problem can be resolved by pulse coding ultrasonic signals, which allows multi-sensors to be fired simultaneously and adjacent objects to be distinguished. Accordingly, the current presents a new simultaneous coded driving system for an ultrasonic sensor array for object recognition in autonomous mobile robots. The proposed system is designed and implemented using a DSP and FPGA. A micro-controller board is made using a DSP, Polaroid 6500 ranging modules are modified for firing the coded signals, and a 5-channel coded signal generating board is made using a FPGA. To verify the proposed method, experiments were conducted in an environment with overlapping signals, and the flight distances for each sensor were obtained from the received overlapping signals using correlations and conversion to a bipolar PCM-NRZ signal.