• Journal of the Korea Society of Computer and Information
• /
• v.17 no.12
• /
• pp.131-136
• /
• 2012

In these days, with the diffusion of mobile equipments, the number of WiFi Access Point (AP) is increasing, and the growth of WiFi AP causes the throughput degradation due to interferences between APs. This recent phenomenon demands the method able to be utilized with current WiFi network to improve the throughput of Wireless LANs. This paper studied the channel assignment method and several throughput enhancement methods to optimize Radio Resource Management (RRM) for distributed infrastructure WLANs. As a result, it was able to put AP independently, improve older allocation error, and improve execution speed.

• The Journal of the Korea Contents Association
• /
• v.11 no.12
• /
• pp.578-585
• /
• 2011

Nowadays, wireless local area networks are widely deployed so that stations can potentially associate with an access point. The AP selection strategy is one of the significant research areas for wireless local area networks. The selection strategy solves the relevant problem is which AP can be selected and associated with a station so that the efficient resource utilization can be obtained. Rather than merely choosing the AP with the strongest received signal strength, however, we calculate effective throughput for each neighboring AP and use it as a basis for AP selection. Referencing the throughput is better than referencing the signal strength only because the network may contain a severe load imbalance. We have performed computer simulations using OPNET modeler in order to verify the performance of the proposed scheme. The results show us that the proposed selection method outperforms that of the conventional one in terms of throughput and delay.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.24 no.1
• /
• pp.87-95
• /
• 2014

Under only authorized AP is allowable environment, rogue AP which is generated by a smartphone tethering can be a serious security breach. To solve rogue AP problem, this paper proposes classifying algorithm of Kernel Support Vector Machine using features of RTT data. Through our experiment, we can detect rogue AP from LTE mobile network.

• Korean Journal of Digital Imaging in Medicine
• /
• v.15 no.2
• /
• pp.7-11
• /
• 2013

Purpose: This study was to evaluate effectiveness of the modified position in scapular AP (anteriopo-sterior) projection. Materials and Methods: From June 2012 to July 2013, scapular AP projection was examined in 108 patients by use of conventional method and in 40 patients by use of modified method. We compared between conventional method and modified method following variables including sex, age, height, weight, and BMI. We measured and compared distance between lateral border of the scapular and the rib to confirm the separation of the scapular from the lung fields including the ribs. Results: The scapular AP projection was technically successful in all patients. There was no significant difference in patient characteristics including sex, age, height, weight, and BMI between conventional method and modified method. The mean distance between lateral border of the scapular and rib in conventional method and modified method was 15.09 mm and 26.33 mm, respectively. Modified method was significantly increased the distance between lateral border of the scapular and rib compared with conventional method (P < .01). Conclusion: The modified position in scapular AP projection was effective method to separate between the scapular and lung fields including the ribs compared with conventional position of scapular AP projection.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2010.10a
• /
• pp.507-509
• /
• 2010

To manage a sensing information such as temperature, humidity efficiently, it's highly recommended suitable application protocol. In this reasons, IETF WG proposed a CoAP protocol, and it's on Internet draft. If it is possible to work on a specific protocol, sensor end nodes and network devices will be managed efficiently. However, end nodes have constrained resources, it is hard to apply a CoAP protocol. In this paper, we analyse a CoAP protocol for USN, and propose a applying method for CoAP over USN nodes.

• Journal of the Korean Society of Radiology
• /
• v.5 no.6
• /
• pp.377-381
• /
• 2011

The purpose of this study is an assessment between the measured value of the nanoDot dosimeter and the calculated value of Non Dosimeter Dosimetry-Method(NDD-M) for entrance surface dose in general radiography. Measurement and calculation of the entrance surface doses were performed for head(AP), abdomen(AP), pelvis(AP), thoracic spine(AP) and lumbar spine(AP). As a result, the relative ratios of the measured value to the calculated value were acquired 1.5-2.1 for each region. Reproducibility acquired 0.035 as a coefficient of variation.

• Journal of the Korea Society of Computer and Information
• /
• v.15 no.3
• /
• pp.55-63
• /
• 2010

On Handoff, existing AP search has chosen one of various APs according to signal strength. However IEEE 802.11 uses Medium Access method with CSMA/CA(Carrier Sensing Multiple Access /Collision Avoidance) that competes to obtain a channel by sharing common medium. For that reason, network performance is heavily affected by the number of nodes and network congestion aside from signal strength. Consequently, in this paper we propose the method that choose one AP which ensures more improved network performance and set up a link, reflecting AP network information in Handoff area, on Handoff in the process of AP selection. We also demonstrate through simulation that it gets maximum performance even in the wireless network which many users concurrently access to, and it has considerable effects on aspects of resources and network management by distribution of users.

• KIPS Transactions on Computer and Communication Systems
• /
• v.6 no.9
• /
• pp.369-376
• /
• 2017

Recently, an RSSI-based fingerprinting localization technology has been widely used in indoor location-based services. In the conventional fingerprinting method, as many APs as possible are used to increase the accuracy of location estimation. In another study, a part of APs having the strongest RSSI signal intensity are selected and used to reduce the time spent for positioning. However, it does not reflect the influence of RSSI occurred from the changes of the surrounding environments such as human movement or moving obstacles in a real environment. The environmental changes may cause the difference between the predicted RSSI signal strength value and the measured value, and thus occur an unpredictable error in the position estimation. Therefore, in order to mitigate the error caused by environmental factors, it is necessary to select APs suitable for indoor positioning estimation considering the changes in the surrounding environments. In this paper, we propose a method to select stable APs considering the influence of surrounding environments and derive a suitable positioning algorithm. In addition, we compare and analyze the performance of the proposed method with that of the existing AP selection methods through experiments.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.39 no.9
• /
• pp.1-11
• /
• 2002

The optimal AP placement for wireless LAN is important factor for improving service quality and reducing cost. Decision of AP placement is depend on radio signal strength, environment factor and logical area property, which is user's frequently posed place. This paper proposes optimal multiple AP placement method based on radio prediction tool. The proposed method can get flexibility in multiple AP placement using user defined parameter and the optimization design uses Hopfield network algorithm. And path-loss model is used for one of radion prediction model. The result of simulation shows that it is efficiently reduces the process to find optimal AP placement. And the proposed optimization design of multiple AP placement can improve service quality for wireless LAN.

• Journal of Institute of Control, Robotics and Systems
• /
• v.20 no.12
• /
• pp.1204-1208
• /
• 2014

As required performance of UAV (Unmanned Aerial Vehicle) becomes more complex and complicated, required positioning accuracy is becoming more and more higher. GPS is a reliable world wide positioning providing system. Therefore, UAV generally acquires position information from GPS. But when GPS is not available such as too weak signal or too less GPS satellites environments, UAV needs alternative positioning system such as network positioning system. RSSI (Received Signal Strength Indicator) based positioning, which is one method of network positioning technologies, determines its position using RSSI measurements containing distance information from AP (Access Point)s. In that method, a selected AP's configuration has strong and tight relationship with its positioning errors. In this paper, for, we additionally account AP's configuration information by adopting DOP (Dilution of Precision) into AP selection procedures and provide more accurate RSSI based positioning results.