• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.12A
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• pp.1303-1310
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• 2007

In IEEE 802.11b wireless network, stations synchronize themselves to the beacons periodically sent by the access point (AP) when they are running in low power mode. Stations stay awake for enough time to receive beacon because it is delayed in AP if the wireless channel has been being used by other traffic at each scheduled instant. In this paper, we propose a method that measures the delay of received beacons and calculates wake-up interval of station to receive the next one. Beacon transmission delay at the AP is analyzed. The proposed method is simulated and its characteristics are described in the analysis. The result measured in terms of station's wake-up interval shows some enhancement in energy consumption.

• Journal of Institute of Control, Robotics and Systems
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• v.16 no.3
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• pp.293-299
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• 2010

The multiple block localization method in a wide area for multiple robots using iGS is proposed in this paper. The iGS is developed for the indoor global localization using ultrasonic and RF sensors. To measure the distance between a mobile robot and a beacon, the tag on the mobile robot wakes up one beacon to send out the ultrasonic signal and measures the traveling time from the beacon to the mobile robot. As the number of robots is increased, the sampling time of localization also becomes longer. Note that only one robot can localize its own position calling beacons one by one during each of the sampling interval. This is a severe constraint for the localization of multiple robots in a wide area. This paper proposes an efficient localization algorithm for the multiple robots in a wide area which can be divided into multiple blocks. For a given block, a master beacon is designated to synchronize robots. By the access of the synchronization signal, each beacon in the selected group sends out an ultrasonic signal. When the robots in the block receive the ultrasonic signal, they can calculate their own locations based on the distances to the beacons, which are obtained by the multiplication of flight time and velocity of the ultrasonic signal. The efficiency of the algorithm is verified through the real experiments.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.6
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• pp.608-614
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• 2008

This paper describes a location tracking system to guide landing process of an Unmanned Helicopter(UMH) exploiting MIT Cricket nodes. For automatic landing of a UMH, a precise positioning system is indispensable. However, GPS(Global Positioning System) is inadequate for tracking the three dimensional position of a UMH because of large positioning errors. The Cricket systems use Time-Difference-of-Arrival(TDoA) method with ultrasonic and RF(Radio Frequency) signals to measure distances. They operate in passive mode in that a listener attached to a moving device receives distance signals from several beacons located at fixed points on ground. Inevitably, this passive type of implementation causes large disturbances in measuring distances between beacons and the listener due to wind blow from propeller and turbulence of UMH body. To cope with this problem, we proposed active type of implementation for positioning a UMH. In this implementation, a beacon is set up at UMH body and four listeners are located at ground area at least where the UMH will land. A pair of Ultrasonic and RF signals from the beacon arrives at several listeners to calculate the position of the UMH. The distance signals among listeners are synchronized with a counter value appended to each distance signals from the beacon.

• Journal of Integrative Natural Science
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• v.11 no.1
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• pp.44-50
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• 2018

In this paper, we propose a context-aware power management (CPM) scheme using beacons to reduce the power consumption of personal computers (PCs). In the proposed CPM scheme, the PC, smartphone, control server, and Internet of Things (IoT) device are necessary. PC users first log in the control server using their smartphones and select PCs to turn on. Then, the selected PCs automatically go into three different modes, i.e., sleep, shutdown, and standby power off modes, in order when the PC users leave the PCs without turning off them. Further, we develop a testbed with the proposed CPM scheme using the Arduino with Bluetooth low energy (BLE) and relay modules. Finally, it is shown that the proposed CPM scheme outperforms the conventional scheme in terms of the power consumption.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.10
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• pp.894-900
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• 2012

Indoor wireless positioning system uses ranging information of beacons in order to precisely estimate a tag location. To estimate distance between each beacons and tag, the system calculates arrival time of a tag pulse with clock of each beacon including independent clock offset. This clock offset seriously affects the performance of ranging and positioning. We propose in this paper a clock offset compensation method to solve this problem. To verify the performance of the proposed method, we simulated location estimation with random clock offset between -1,000ppm and 1,000ppm, and the result shows that the proposed scheme effectively solves the clock offset problem.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1A
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• pp.101-108
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• 2007

There nay be collisions among beacons from several full function devices in IEEE 802.15.4 sensor networks. These collision of beacons may cause devices to lose time synchronization, and thus be unable to association. To solve this problem, the IEEE 802.15.4b defines a new Post Beacon Period(PBP), but it does not still alleviate the beacon collision problem. In this paper, we propose two automatic beacon alignment schemes that a node itself can decide its beacon start time using its short address that has been assigned during association. We also simulate and investigate our proposed automatic beacon collision avoidance schemes using NS-2 simulator.

• Journal of KIISE:Information Networking
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• v.37 no.6
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• pp.431-443
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• 2010

In this paper, we propose a range-free localization method that can improve the estimation accuracy of Approximate Point in Triangle(APIT), which is the representative localization method for low cost wireless sensor networks. Specifically, we propose extended-APIT(e-APIT) method, which minimizes the error in deciding whether an object is in an area formed by three beacons. We also propose a way to improve the localization by narrowing down the potential localization area using the signals from neighboring beacons. According to the simulation performed, the proposed e-APIT method demonstrated noticeable accuracy improvement over the conventional APIT method.

• Proceedings of the Korea Information Processing Society Conference
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• 2013.05a
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• pp.610-613
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• 2013

Vehicular Ad Hoc NETwork (VANET), a subclass of Mobile Ah Hoc NETwork (MANET) has been a tech-buzz for the last couple of decades. VANET, yet not deployed, promises the ease, comfort, and safety to both drivers and passengers once deployed. The by far most important factor in successful VANET application is the data dissemination scheme. Such data includes scheduled beacons that contain whereabouts information of vehicles. In this paper, we aim at regularly broadcasted beacons and devise an algorithm to disseminate the beacon information up to a maximum distance and alleviate the broadcast storm problem at the same time. According to the proposed scheme, a vehicle before re-broadcasting a beacon, takes into account the current vehicular density in its neighborhood. The re-broadcasters are chosen away from the source of the beacon and among the candidate re-broadcasters, if the density in the neighborhood is high, then the candidate rebroadcaster re-broadcasts the beacon with high probability and with low probability, otherwise. We also performed thorough simulations of our algorithms and the results are sound according to the expectations.

• Journal of the Semiconductor & Display Technology
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• v.22 no.2
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• pp.50-55
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• 2023

Due to the unavailability of global positioning system (GPS) indoors, various indoor pedestrian positioning methods have been designed to estimate the position of the user using received signal strength (RSS) measurements from radio beacons, such as wireless fidelity (WiFi) access points and Bluetooth low energy (BLE) beacons. In indoor environments, radio-frequency (RF) signals are unpredictable and change over space and time because of multipath associated with reflection and refraction, shadow fading caused by obstacles, and interference among different devices using the same frequencies. Therefore, the outliers in the positional information obtained from the indoor positioning method based on RSS measurements occur often. For this reason, the performance of the positioning method can be degraded by the characteristics of the RF signal. To resolve this issue, a map-matching (MM) algorithm based on maximum probability (MP) estimation is applied to the indoor positioning method in this study. The MM algorithm locates the aberrant position of the user estimated by the positioning method within the limits of the adjacent pedestrian passages. Empirical experiments show that the positioning method can achieve higher positioning accuracy by leveraging the MM algorithm.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.10a
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• pp.180-182
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• 2021

This paper proposes a method for estimating the location of a user using a beacon to provide a service in an indoor environment. To estimate the location using the beacon, a Gaussian filter was applied to the RSSI value of the beacon, and the distance conversion function was obtained through the filtered RSSI value to estimate the tag location by trilateration. Then, in the indoor space where the beacons are installed, the location estimation accuracy of 8 places where 3 beacons are at a certain distance was confirmed. As a result, it was possible to confirm the position estimation accuracy of ±0.097 standard deviation and 0.242 distance error.