Minkyu Lee

Building a Practical Wi-Fi-Based Indoor Navigation System

This article presents the seven-step process involved in building a practical Wi-Fi-based indoor navigation system, which was implemented at the COEX complex in Seoul, Korea, in October 2010. The article describes the primary activities in each step using the COEX example. More than 200,000 users have downloaded the system since its first release. The successful launch of the COEX indoor navigation system suggests that indoor navigation is becoming a reality.

Voronoi Tessellation Based Interpolation Method for Wi-Fi Radio Map Construction

The fingerprint-based approach for positioning in WLAN has been drawing great attention these days. However, the approach usually requires tremendous time and efforts to collect location fingerprints for the target area. In this paper, we propose an interpolation method based on Voronoi tessellation to significantly reduce such calibration efforts and to improve accuracy. Unlike other interpolation methods, our method refines the propagation model for each cell of the target area tessellated by a higher-order Voronoi diagram. Consequently, our method can take into account the signal fading caused by walls and obstacles more accurately. The proposed method significantly outperformed other interpolation methods in accuracy.

Crowdsourced radiomap for room-level place recognition in urban environment

The proliferation of WLAN infrastructures has facilitated numerous indoor localization techniques using WLAN fingerprints. In particular, identifying a room or a place in urban environments could be usefully utilized in many application domains such as ubiquitous health. However, it is not straightforward how to bootstrap such a localization system because WLAN fingerprints of all places must be available in advance. In this paper, we propose a crowdsourcing approach for indoor place recognition. The key idea is to build an open participatory system through which users can contribute fingerprints. As the database size increases, it can provide place recognition service. We conducted an extensive experimental study at a university campus to demonstrate the performance of the proposed method in terms of recognition accuracy. We also studied key factors that could undermine the crowdsourcing approach such as fingerprint density, incorrect contribution, uneven contribution, and device heterogeneity.

THE-MUSS: Mobile u-health service system

In this paper, we introduce a mobile u-health service system called THE-MUSS. THE-MUSS supports the development and running of u-health services with functions, modules, and facilities that are commonly required for various mobile u-health services. Aiming to achieve reusability and evolvability design goals, basic modules to support bio-signal capturing, processing, analysis, diagnosis, and feedback are developed and stacked in the layered architecture of THE-MUSS. A U-health service platform, design tool, portal, and matrix-based disease group identification method are the major components constituting the THE-MUSS architecture. We confirmed that THE-MUSS is practically useful for mobile u-health services by developing mobile stress and weight management services on THE-MUSS. The more u-health services are developed in THE-MUSS, the better services it can provide in the future.

Energy-Efficient Location Logging for Mobile Device

Location logging is a technique that continuously records user’s location using various location sensing and positioning technologies. Location logs and information derived from those logs can be useful contexts for various applications. However, previous research related to recording and handling location logs failed to seriously consider heavy battery consumption. Heavy battery consumption is a serious problem in location logging research and applications, and it has obstructed location logging applications to be widely used. In this paper, we present Variable Rate Logging (VRL) mechanism to maximize battery life of continuous logging for user’s location with minimum loss of logging quality. Our mechanism can optimize any application which requires continuous recording of user’s location and dramatically extend its battery life. Evaluation results show that Variable Rate Logging mechanism has 143% longer battery life than fixed rate logging.

THE-MUSS: Mobile U-Health Service System

In this paper, we introduce a mobile u-health service system, named THE-MUSS, which supports u-health service development and running, with functions, modules, and facilities that are commonly required for various mobile u-health services. Basic modules to support bio-signal capturing, processing, analysis, diagnosis, feedbacks are prepared and stacked in the system. Reusability and evolvability are elicited as the primary design goals to achieve in developing THE-MUSS after the understanding of u-health service characteristics. U-health service platform, u-health ontology incorporated u-health service design tool, Matrix based disease group identification framework, and u-health portal are the major components constructing the layered architecture of THE-MUSS. Mobile stress and weigh management services are developed on THE-MUSS to confirm and evaluate the usefulness of THE-MUSS in developing mobile u-health services. According to the evaluation, it turned out that THE-MUSS has strength in reusability and evolvability, but also in system flexibility, adaptability, interoperability, and guideline provision for developing u-health services.

Elekspot: A Platform for Urban Place Recognition via Crowdsourcing

The proliferation of Wi-Fi infrastructures has facilitated numerous indoor localization techniques using Wi-Fi location fingerprints. They make it possible to identify a room or a place in urban environment, which is especially important in enabling many interesting location-based services. As there are too many rooms and places such as cafes and restaurants to be recognized in urban environment, the crowdsourcing approach has been proposed to collect Wi-Fi location fingerprints based on user participation. However, its actual deployment in a large-scale urban environment presents numerous design and implementation challenges due to urban characteristics such as a large crowd, dense region, and device diversity. This paper presents Elekspot system, whose design goal is to support system scalability, device heterogeneity, robustness against lack of contributions, and localization accuracy. Through several experiments and implementation of actual applications targeting urban places we confirmed that the architecture and methods of Elekspot can effectively meet the design goals.

A framework for personalized Healthcare Service Recommendation

Development of the Internet enables numerous healthcare services to be available to many service consumers. As a result, many brokering web sites such as healthcare service portals and search engines are deployed to support userspsila choice. However, to provide better healthcare to the novice users, systems need more sophisticated mechanism for healthcare recommendation. In this paper, we propose healthcare service recommendation framework (HSRF) that considers health status and various contexts of each user. HSRF arranges healthcare services based on medical similarities between user and services. We successfully implemented the framework and confirmed its functionality and feasibility.

Open radio map based indoor navigation system

In this presentation, we introduce an open radio map based indoor navigation system. The system is implemented on a Google android phone and tested on 3rd floor, Main-building, KAIST Munji Campus, Korea. The open radio map for the system is constructed by partly participatory approach. That is, the radio map data for rooms and laboratories are collected by ordinary users of smart phones, and for corridors by trained experts. We confirmed that the open radio map based indoor navigation service has a high potential to be used in real fields if the open radio map accumulates sufficient amount of Wi-Fi fingerprints.

Ubiscript: A Script Language for Ubiquitous Environment

Many distributed and heterogeneous services and devices are accessible in ubiquitous computing environment, so interoperating those services and devices is one of the key tasks in implementing ubiquitous applications. We used to use script languages in integrating such interoperating components and services. However currently available most script languages are not suitable for ubiquitous environment because there are so diverse forms of interoperation targets such as service objects, web, legacy objects and programmable devices. So it is worthwhile designing a new script language well-suited to ubiquitous environment. In this paper, we propose a new script language, called Ubiscript, for the ubiquitous environment. We develop and adopt several unique language features such as remote scope, multiple contexts, web and legacy objects, remote exception handling, etc. in Ubiscript to overcome the limitations of conventional script languages. In this paper, we also describe the implementation of Ubiscript and its runtime system. A couple of ubiquitous applications were developed in Ubiscript, and the applications are tested on the runtime system. According to our experiences and evaluation, Ubiscript turned out to have a high potential in its expression power and contribution to improving ubiquitous application developers’ productivity.