• Journal of Information Processing Systems
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• 제8권1호
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• pp.1-20
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• 2012

The most important criterion for achieving the maximum performance in a wireless mesh network (WMN) is to limit the interference within the network. For this purpose, especially in a multi-radio network, the best option is to use non-overlapping channels among different radios within the same interference range. Previous works that have considered non-overlapping channels in IEEE 802.11a as the basis for performance optimization, have considered the link quality across all channels to be uniform. In this paper, we present a measurement-based study of link quality across all channels in an IEEE 802.11a-based indoor WMN test bed. Our results show that the generalized assumption of uniform performance across all channels does not hold good in practice for an indoor environment and signal quality depends on the geometry around the mesh routers.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권3호
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• pp.243-257
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• 2010

Rapid developments in wireless sensor networks have extended many applications, hence, many studies have developed wireless sensor network positioning systems for indoor environments. Among those systems, the Global Position System (GPS) is unsuitable for indoor environments due to Line-Of-Sight (LOS) limitations, while the wireless sensor network is more suitable, given its advantages of low cost, easy installation, and low energy consumption. Due to the complex settings of indoor environments and the high demands for precision, the implementation of an indoor positioning system is difficult to construct. This study adopts a low-cost positioning method that does not require additional hardware, and uses the received signal strength (RSS) values from the receiver node to estimate the distance between the test objects. Since many objects in indoor environments would attenuate the radio signals and cause errors in estimation distances, knowing the path loss exponent (PLE) in an environment is crucial. However, most studies preset a fixed PLE, and then substitute it into a radio propagation loss model to estimate the distance between the test points; such method would lead to serious errors. To address this problem, this study proposes a Path Loss Exponent Estimation Algorithm, which uses only four beacon nodes to construct a radio propagation loss model for an indoor environment, and is able to provide enhanced positioning precision, accurate positioning services, low cost, and high efficiency.

• 설비공학논문집
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• 제19권2호
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• pp.202-211
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• 2007

Ventilation system is being recommended as an effective tool to improve indoor air quality (IAQ) in apartment houses. Recently, in Korea, apartment house suppliers must establish ventilation system in apartment houses in law. In this study, improvement of IAQ by establishing mechanical ventilation system at apartment house was investigated by mockup test. Seven apartment houses were arranged for the test and improvement of IAQ was examined under the various conditions of ventilation rates, ventilator type and duct works. The results of this study show that IAQ in the test houses which were established mechanical ventilation system was improved about from 30% to 40% compared with IAQ in the apartment house which was not established ventilation system. However, there were no apparent concentration differences between the cases of changing ventilation rates, ventilator types and ductworks.

• 제어로봇시스템학회논문지
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• 제14권9호
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• pp.963-968
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• 2008

A new method to deal with GPS indoor positioning by means of time synchronized switching GPS repeater has been developed by authors[1]. But the developed indoor positioning system has problems. Therefore, we proposed a method for indoor positioning using GNSS Repeater-Assisted. To solve the 3-dimensional user's position, the 4 or more retransmission antennas are needed in the previously proposed methods. If a GPS repeater periodically transmits the signal like as pseudollite, the information for assisting an acquisition and tracking can be informed to receiver. Then, the user position can be calculated using the induced weak signal. The advantage of the proposed algorithm is use of only 1 re-transmission antenna because the re-transmitted signal are not used for positioning but used for assisting an acquisition and tracking weak signals induced indoor. We analyze the propose algorithms through the experiment and performed the test of feasibility.

• Journal of Positioning, Navigation, and Timing
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• 제12권2호
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• pp.91-100
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• 2023

The existing indoor localization method using Wi-Fi fingerprinting has a high collection cost and relatively low accuracy, thus requiring integrated correction of convergence with other technologies. This paper proposes a new method that significantly reduces collection costs compared to existing methods using Wi-Fi fingerprinting. Furthermore, it does not require labeling of data at collection and can estimate pedestrian travel paths even in large indoor spaces. The proposed pedestrian movement path estimation process is as follows. Data collection is accomplished by setting up a feature area near an indoor space intersection, moving through the set feature areas, and then collecting data without labels. The collected data are processed using Kernel Linear Discriminant Analysis (KLDA) and the valley point of the Euclidean distance value between two data is obtained within the feature space of the data. We build learning data by labeling data corresponding to valley points and some nearby data by feature area numbers, and labeling data between valley points and other valley points as path data between each corresponding feature area. Finally, for testing, data are collected randomly through indoor space, KLDA is applied as previous data to build test data, the K-Nearest Neighbor (K-NN) algorithm is applied, and the path of movement of test data is estimated by applying a correction algorithm to estimate only routes that can be reached from the most recently estimated location. The estimation results verified the accuracy by comparing the true paths in indoor space with those estimated by the proposed method and achieved approximately 90.8% and 81.4% accuracy in two experimental spaces, respectively.

• 한국전문물리치료학회지
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• 제24권3호
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• pp.1-9
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• 2017

Background: The method of measuring the walking function of patients with chronic stroke differs depending on patients walking capability and environmental conditions. Objects: This study aimed to demonstrate the influences of walking capacity and environmental conditions on the results of short- and long-distance walk tests in patients with chronic stroke. Methods: Forty patients with chronic stroke volunteered for this study, and allocated to group-1 (<.4m/s, household walking, $n_1=13$), group-2 (.4~.8m/s, limited community ambulation, $n_2=16$), and group-3 (>.8m/s, community ambulation, $n_3=11$) according to their walking capacity. The 10-meter walk test (10MWT) and 6-min walk tests, (6MWT) were used to compare the short- and long-distance walk tests results, which were randomly performed under indoor and outdoor environmental conditions. Results: The comparison of the results obtained under the indoor and outdoor conditions revealed statistically significant differences between the groups in the 6MWT and 10MWT (p<.05). Post-hoc tests' results showed significant differences between groups-1 and -2 and between groups-1 and -3 in the 10MWT, and between group-1 and -3 in the 6MWT. Furthermore, in group-2 the 10MWT and 6MWT results significantly differed between the indoor and outdoor conditions, and the values measured under the indoor and outdoor conditions significantly differed between 10MWT and 6MWT (p<.05). Group-3 showed a significant difference in 10MWT results between the indoor and outdoor conditions (p<.05). Conclusion: These findings suggest that the results of the short- and long-distance walk tests may differ depending on the walking capacity of patients with chronic stroke and the environmental condition under which the measurement is made, and these effects were greatest for the patients with the limited community ambulation capacity.

• Journal of Mechanical Science and Technology
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• 제19권4호
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• pp.1001-1005
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• 2005

This paper evaluates the performance of ventilation for the removal of indoor pollutants as a function of ventilation rate and the number of occupants in a test room and school classroom. An experimental apparatus consists of a test room, a tracer gas supply system, a gas detector, and a fan for ventilation air supply with a controller. The ventilation performance is evaluated in a step-down method based on ASTM Standard E741-83 using $CO_{2}$ gas as a tracer gas in the test room of 35 $m^{3}.$ For the ventilation air flow rate of 1.0 ACH, a recommended ventilation flow rate of Korea school standard for acceptable indoor air quality in the case of one person, CO_{2}$ gas concentration decreases up to $55{\%}$ within 50 minutes without occupancy and increases up to $75{\%}$ in the case of one occupant. Also indoor air quality at the school classroom is investigated experimentally.

• 한국안전학회지
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• 제30권4호
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• pp.142-150
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• 2015

A portable recoilless guided missile generates a strong back blast and impulsive noise at the nozzle when it launches. In the case of indoor operations, the hazard of the blast noise from a recoilless weapon increases due to limited indoor spaces. Also, the noise levels determine the operational feasibility of a weapon; therefore, it is important to predict the blast noise levels distribution in the indoor space in advance. In addition, computational fluid dynamics (CFD) method generally used for fluid related simulations, requires high computing cost and time to simulate the whole domains. The domain includes both blast wave region and large and various indoor space region. Therefore, an efficient method for predicting the far-field noise level within a short time should be developed. This paper describes an analysis model for predicting the indoor noise distributions by considering the shape effect of the building within a short time. A new developed blast wave model was implemented using the noise source. Additionally, noise reflections at the closed surfaces such as walls and noise transmissions at the opened surfaces such as windows and doors were considered in calculating the noise levels. The predicted noise levels were compared with the experimental data obtained from the indoor launch test to validate the reliability of program.

• 한국지역사회생활과학회지
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• 제26권1호
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• pp.115-126
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• 2015

The study investigates the clothes-wearing behaviors of female college students based on differences in indoor heating systems and cold sensitivity. The respondents included a total of 281 female college students living in South Korea and China. Data were analyzed through an ANOVA and, a paired t-test based on SPSS 21.0. Korean students were less dependent on winter clothing than Chinese students for the whole body parts except for the trunk. Korean students were more likely to feel coldness more but wore less clothing. Korean students' clothes-wearing behaviors with respect to coldness depended on the indoor heating system. Korean students tended to buy warmer clothing, although they preferred not to wear undergarments and tended to wear and to wear less winter clothing. Chinese students showed more active clothes-wearing behaviors to keep their feet warm. Finally, groups divided by indoor heating systems and cold sensitivity showed different clothes-wearing behaviors in comparison to those groups based only on indoor heating systems. Even in similar weather conditions, clothes-wearing behaviors for cold adaptation depended on the indoor heating systems and cold sensitivity. The results suggest that this perspective should be taken into consideration when evaluating clothes-wearing behaviors of certain groups or individuals.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.330-333
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• 2003

In this thesis. the application of the synchronizing control of the intelligent indoor lift system is showed. The separate axes of the indoor lift system are driven independently. PID controller, synchronous flexible logic compensating method and tilt sensor are applied to enhance the performance of the intelligent indoor lift system. the tilt sensor senses the horizontal error of the whole system. PID controller and synchronous flexible logic are used to compensate the synchronous errors of both the separate axes and whole system to be zero. Namely, using not the hardware coupling but the software algorithm. the indoor life system is operated without the error. Before applying the real system, the simulation using matlab testifies the possibility of the lift system. And the realization of the system is demonstrated with two DC servo motors. In the experiment test, flexible logic to compensate the synchronous error is chosen by the comparative method. the indoor lift system has to be considered the loading factor as the disturbance. Because the intelligent indoor lift system is developed to support the patients who don't change for themselves to move. finally, the system which considers the weight of the patient as the disturbance can carry the patients safely without synchronous and position error.