• Journal of Computing Science and Engineering
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• v.4 no.2
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• pp.173-187
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• 2010

Recent technological advances in mobile communication systems have made explosive growth in the number of mobile device users worldwide. One of the most important issues in designing a mobile computing system is location management of users. The hierarchical systems had been proposed to solve the scalability problem in location management. The scalability problem occurs when there are too many users for a mobile system to handle, as the system is likely to react slow or even get down due to late updates of the location databases. In this paper, we propose a top-down clustering algorithm for hierarchical location database systems in a wireless network. A hierarchical location database system employs a tree structure. The proposed algorithm uses a top-down approach and utilizes the number of visits to each cell made by the users along with the movement information between a pair of adjacent cells. We then present a modified algorithm by incorporating the exhaustive method when there remain a few levels of the tree to be processed. We also propose a capacity constraint top-down clustering algorithm for more realistic environments where a database has a capacity limit. By the capacity of a database we mean the maximum number of mobile device users in the cells that can be handled by the database. This algorithm reduces a number of databases used for the system and improves the update performance. The experimental results show that the proposed, top-down, modified top-down, and capacity constraint top-down clustering algorithms reduce the update cost by 17.0%, 18.0%, 24.1%, the update time by about 43.0%, 39.0%, 42.3%, respectively. The capacity constraint algorithm reduces the average number of databases used for the system by 23.9% over other algorithms.

• The Journal of Information Technology
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• v.12 no.2
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• pp.1-12
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• 2009

China first started its mobile phone services in 1987, and the number of users has exponentially increased so that it reached 700 millions in January 2009. Currently China's 2G(GSM) users is 650 millions. These 2G (GSM) services have an advantage of the capability to use the mobile phone with a SIM (Subscriber Identity Modul) card, one kind of smart cards, inserted into it. However, due to the security vulnerability of SIM cards being used within China's 2G (GSM) services, SIM cards cloning. Problems concerning mobile phone surveillance towards a designated person by illegal cloning ESN and IMSI have recently risen to be a massive social issue within Korea as well. These studies have experimented the possibility of SIM cards clone in various mobile communication corporations using 2G (GSM) in China, and hence discovered the security vulnerability such as the incoming outgoing, SMS service and additional services on mobile phones using clone SIM cards.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.5 s.182
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• pp.119-127
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• 2006

Design structure of a mobile phone has been changed to a converged style, which has so many functions. However, the converged mobile phone could not satisfy the users who want to use only specific functions, so with Axiomatic Design, we have studied for making a proposal to set up the new concept. The goal of this study is to derive a general solution with Axiomatic Design to verify the Independence. By enhancing the existing design model and differentiating the function of mobile phone, user will be able to choose desirable products, which have only specific functions and/or specific parts. First of all, we checked the Independence about the existing design model. Then, we developed the new design model with the idea that base mobile phone should have basic functions and additional functions can be separated, surely be connected when users want.

• Journal of Industrial Technology
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• v.27 no.A
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• pp.131-139
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• 2007

The recent advance in wireless network technologies has enabled the streaming media service on the mobile devices such as PDAs and cellular phones. Since the wireless network has low bandwidth channels and mobile devices are actually composed of limited hardware specifications, the transcoding technology is needed to adapt streaming media to given mobile devices. Futhermore owing to the diversity of bandwidth in the wireless network by reason of mobile users' movements and environments, it is difficult to provide stable QoS. In this paper, the autonomic multimedia transcoding system is proposed in order for users to provide network adaptive QoS. Our proposed system is based on the estimation of available bandwidth in wireless network for seamless multimedia streaming service. The proposed system is designed and implemented for various mobile clients. In experiments, we evaluate its seamless multimedia streaming and the adaptation transcoding bit rate according to the changes of bandwidth in wireless network.

• Journal of Information Technology Applications and Management
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• v.12 no.3
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• pp.97-109
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• 2005

The internet and wireless communication technologies are creating ubiquitous environments in which various services are expected anytime and anywhere. Many hardware facilities have been developed and system structures are suggested for mobile services to realize a ubiquitous computing environment with appropriate quality. But these applications are not designed in the consideration of the general capabilities to perform user's wireless and mobile communication/transaction. Consequently, different needs from users are not sufficiently satisfied yet. In this study, we suggest structure of the emerging network system for mobile commerce that provides users with seamless and ubiquitous environments using location information which exploit context-aware technology.

• Journal of Information Technology Services
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• v.9 no.2
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• pp.163-177
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• 2010

In this paper, we consider a channel ordering problem that seeks to maximize the service quality in mobile radio communication systems. If a base station receives a connection request from a mobile user, one of the empty channels belonging to the base station is assigned to the mobile user. In case multiple empty channels are available, we can choose one that incurs least interference with other channels assigned to adjacent base stations. However, note that a pair of channels that are not separated enough generates interference only if both channels are assigned to mobile users. That is, interference between channels may vary depending on the channel assignment sequence for each base station and on the distribution of mobile users. To find a channel assignment sequence that seems to generate minimum interference, we develop an optimization model considering various scenarios of mobile user distribution. Simulation results show that channel assignment sequence determined by the scenario based optimization model significantly reduces the interference provided that scenarios and interference cost are properly generated.

• Journal of the Korean Society of Systems Engineering
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• v.17 no.2
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• pp.98-105
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• 2021

As the average life expectancy is rising, the population is aging and the number of chronic diseases is increasing. This has increased the importance of healthy life and health management, and interest in mobile health services is on the rise thanks to the development of ICT(Information and communication technologies) and the smartphone use expansion. In order to meet these interests, many mobile services related to daily health are being launched in the market. Therefore, in this study, the characteristics of users who actually use mobile health services were analyzed and a predictive model applied with machine learning modeling was developed. As a result of the study, we developed a prediction model to which the decision tree and ensemble methods were applied. And it was found that the mobile health service users' continued use can be induced by providing features that require frequent visit, suggesting achievable activity missions, and guiding the sensor connection for user's activity measurement.

• Proceedings of the Korea Information Processing Society Conference
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• 2023.05a
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• pp.104-106
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• 2023

The mobile crowdsensing platform obtains sensing data from mobile users, and the involvement of the public increases the untrustworthy of collected data. In order to distinguish factual data from inaccurate data provided by untrustworthy users, the truth discovery method has been introduced for accurate data aggregation in mobile crowdsensing (MCS). To explore the application of truth discovery in mobile crowdsensing, we overview the general concepts of truth discovery algorithms. Finally, we summarize the main existing application prospects of truth discovery in mobile crowdsensing.

• Journal of Information Processing Systems
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• v.12 no.4
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• pp.612-630
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• 2016

As mobile augmented reality technologies are spreading these days, many users want to produce augmented reality (AR) contents what they need by themselves. To keep pace with such needs, we have developed a mobile AR contents builder (hereafter referred to as MARB) that enables the user to easily connect a natural marker and a virtual object with various interaction events that are used to manipulate the virtual object in a mobile environment so that users can simply produce an AR content using natural photos and virtual objects that they select. MARB consists of five major modules-target manger, virtual object manager, AR accessory manager, AR content manager, and AR viewer. The target manager, virtual object manager and AR accessory manager register and manage natural target markers, various virtual objects and content accessories (such as various decorating images), respectively. The AR content manger defines a connection between a target and a virtual object with enabling various interactions for the desired functions such as translation/rotation/scaling of the virtual object, playing of a music, etc. AR viewer augments various virtual objects (such as 2D images, 3D models and video clips) on the pertinent target. MARB has been developed in a mobile application (app) format in order to create AR contents simply using mobile smart devices without switching to a PC environment for authoring the content. In this paper, we present the detail organizations and applications of MARB. It is expected that MARB will enable ordinary users to produce diverse mobile AR contents for various purposes with ease and contribute to expanding the mobile AR market based on spread of a variety of AR contents.

• Journal of Korea Multimedia Society
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• v.7 no.5
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• pp.689-697
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• 2004

Rapid advances in mobile computing and the availability of wireless communications will soon provide mobile users with the ability to access data regardless of the location of the user or of the data. SRA(Static Replica Allocation) that is traditional scheme has been used for the replication method on the server. This replicates the data on the replica server after a moving host has been transferred to the cell. This strategy is simple and can easily relocate data. However, if a mobile user does not exist in the cell, the replicated data can be deleted in order to maintain data consistency. In addition to, if the mobile host leaves from replicated cell, it is difficult to access data in terms of replication route. Therefore, this paper proposes a new method of relocation based on data consistency strategy called USRAC(User Selection Replica Allocation based on Consistency) and also analyzes access cost according to the moving rate of mobile users, according to the access rate of mobile hosts, and according to the number of cells of mobile users and mobile hosts.