Surgwon Sohn

Optimization of base stations positioning in mobile networks

Cell planning is a very complex task because many aspects should be taken into account including the traffic distribution, geography, antenna height of base stations, frequency, and so forth. This becomes more complicated when several constraints are considered such as the quality of service, maximum output power of transmitters, types of power control, and other network requirements. The problems are assignment of mobile stations to the appropriate base station and finding good locations of the base stations. This paper presents a constraint satisfaction problem model for base station location in 3G W-CDMA uplink environments. This is similar to a warehouse location problem, so it is NP-hard and consequently cannot be practically solved by exact methods for real size networks. Thus we apply constraint satisfaction techniques such as variable ordering and value ordering to get good approximate solutions. The algorithm has been implemented by using both integer programming and constraint programming.

Graph Coloring Algorithms and Applications to the Channel Assignment Problems

This paper presents graph coloring algorithms and their applications to the channel assignment problems. Two application problems of frequency assignment of low power FM broadcasting and reader collision problem of RFID system are modeled as graph coloring problems. Instead of performing an exhaustive search for the optimal result, we provide both search space reduction and variable ordering heuristics to obtain good approximate solutions. Constraint optimization modeling and variable ordering enforce the backtracking process in graph coloring algorithms, so the search space is greatly reduced and the approximate solution is found quickly. A great deal of outstanding work on graph coloring algorithms is described and applied to the simulation results.

Implementation of Ubiquitous Health Care System for Active Measure of Emergencies

The present study discusses the construction of a ubiquitous health care system that can cope actively with urgent situations of chronic disease patients who can lead everyday life despite their chronic diseases. If a patients emergency is detected by personal health care host (PHCH), which is composed of USN, electronic stethoscope, GPS, CDMA and RFID, a text message containing position information is sent immediately to the hospital and the guardians mobile terminal so that they can take an action immediately. In particular, data from accelerometers and vibration sensors, which are composed of ubiquitous sensors, are learned using the back-propagation network algorithm, therefore emergencies such as syncope and convulsion are determined actively. The experiments show that this system is very effective to find emergencies promptly for chronic disease patients who cannot take care of themselves and it is expected to save many lives.

Feasibility study on the use of wireless accelerometers in the experimental modal testing

This paper presents a modal parameter estimation of a cantilevered steel beam using low-cost wireless accelerometers for structural health monitoring. To demonstrate the feasibility of using wireless accelerometers, the frequency response functions (FRFs) for the beam are measured. A curve-fitting algorithm is then applied to extract the modal parameters, such as natural frequencies, damping ratios, and mode shapes. These dynamic characteristics of the cantilever beam are acquired and interpreted through the FRFs by the commercial analyzing software. Experimental results show that wireless accelerometers can successfully determine the dynamic properties of the cantilever beam. This paper provides the analytical basis of applying wireless accelerometers to the experimental modal analysis and supports for the feasibility of cantilever beam modal testing using low-cost wireless accelerometers.

Solving a constraint satisfaction problem for frequency assignment in low power FM broadcasting

We present an algorithm to solve the frequency assignment problem for low power FM broadcasting. To get a good suboptimal solution, some heuristics such as k-coloring variable ordering and mostly-used value ordering rule are provided. They enforce the backtracking process in a constraint satisfaction problem, so both the search space and computing time are greatly reduced. A lot of outstanding work on graph coloring problems has been achieved, and the theoretical lower bound of the chromatic number of random graph is one of them. Comparison between the theoretical lower bound and our computed approximate solution has been made for evaluation of proposed algorithm.

Development of u-Health Care System for Prompt Perception of Emergencies

This study discusses the development of a u-Health care system that can detect quickly and cope actively with emergent situations of chronic disease patients who lead everyday life. If a patient`s emergent situation is detected by personal health care host(PHCH), which is composed of acceleration and vibration sensors, GPS, and CDMA communication module, a text message on the patient`s current location is transmitted to the hospital and the guardian`s mobile terminal so that they can cope with the situation immediately. Especially, the system analyzes data from sensors by using neural network and determines emergent situations such as syncope and convulsion promptly. The exact location of patients can also be found in the electronic map by using GPS information. The experiments show that this system is very effective to find emergencies promptly for chronic disease patients who cannot take care of themselves and it is expected to save many lives.

Design of Transducer Interface Agent and its Protocol for WSN Middleware

This paper presents a simple design and implementation of a transducer interface agent. The agent communicates with a middleware for wireless sensor networks, and can be installed on the PC or any small gateway devices. The agent’s chief end is to replace the network capable application processor (NCAP) and wireless transducer interface module (WTIM) with the agent itself in the IEEE 1451 family of standards. In order to support various non-standardized transducers, we propose to use a variety of configuration template files instead of modifying the agent itself. While a wrapper of the transducer interface agent manages various types of sensors, the controller deals with many actuators. In order to justify the usefulness of the proposed agent and its protocol, we carried out health monitoring experiments in a mock-up railway system and verified the efficiency.

Channel and Time Slot Allocation for Dense RFID Networks

This paper presents a constraint satisfaction approach to the reader collision problem in dense mode environments for static RFID networks. Our method assigns available channels and time slots to the RFID readers to increase the read rate while satisfying all the interference constraints. We model the problem with a hybrid frequency and time division multiplexing constraint satisfaction for reader anti-collision and assign workable channels and time slots to each reader using backtracking search algorithms. A depth-first-search based on backtracking was performed to find solutions to constraint satisfaction problems. Instead of performing an exhaustive search for the optimal result, we adopted good variable ordering heuristics as branching strategies where the search can be completed quickly. Thus, the search space is greatly reduced, and approximate solutions are found instantly. To find appropriate heuristics, we applied a problem classifying rule to determine the quality of the variable ordering heuristics. Computer simulations of the comparable performance of some variable ordering algorithms in the channel and time slot allocation for dense RFID networks are presented.

A Study on Context Aware Middleware Design and Application

This paper describes a design and application of middleware that is essential to the context-aware system. We define a transducer interface protocol in order to deal with a variety of context data. For the purpose of systematic process of data between middleware modules, a message oriented middleware is designed and implemented. Memory improves the performance of high-performance computing system compared to previous strategies. Context aware middleware adopts service oriented architecture so that functions in modules may be independent and scalability can be remarkable. Using messages across modules decreases the complexity of the application development. In order to justify the usefulness of the proposed context aware middleware, we carried out our experiments in bridge health monitoring system and verified the efficacy.

An Ontology-based Context Aware Model for the Implementation of Integrated Security Control System

Abstract In this paper, we describe an ontology-based context aware model that collects context information from USN sensor and CCTV image and reasons about context in order to development an integrated security control system in the industrial environments. The context model represents autonomous and heterogeneous data as ontologies and recognizes the context through DL(description logic) inference in the smart computing environment. We expect that the integrated security control system can automatically detects the risk in the industrial field and reduces the safety and security incidents by applying this context model to the system. Key Words : Ontology, Context aware, Security control system, Inference, Description logic 이 논문은 2009년도 산학협동재단의 학술연구비 지원을 받아 수행된 연구임 * 교신저자 : 손석원(sohn@hoseo.edu)접수일 10년 03월 24일 수정일 (1차 10년 05월 05일, 2차 10년 05월 18일, 3차 10년 06월 09일) 게재확정일 10년 06월 18일 1. 서론 산업현장에서 관제시스템은 단순히 보안측면의 관제 보다는 시설 및 설비, 소방 등 다수의 설비나 시설물을 관제대상으로 하고 있다. 예를 들어 냉난방, 조명과 같은 시설 및 설비의 실시간 감시제어, 소방 설비의 실시간 감시제어 및 CCTV를 이용한 영상 감시등 다양한 종류의 관제시스템이 설치, 운영되고 있으며 이를 조작하는 작업자는 각각의 시스템을 별도로 운영, 조작하고 있다. 이로 인한 보안관제의 효율성의 저하로 개인, 기업 및 사회적인 손실은 매우 커지고 있는 실정이다. 이에 대한 대응책으로 RFID (Radio Frequency IDentification)와 USN (Ubiquitous Sensor Network) 센서 등과 같은 IT 기술을 이용한 통합보안관제 시스템의 구축이 요구되고 있다. 특히 CCTV 기반의 영상감시는 감시 인력이 단순히 모니터를 통하여 감시해야 하기 때문에 위험이 증가하고 인력활용의 효율성이 낮다. 다수의 카메라가 있음에도 감시자들이 전부 모니터링 할 수 없기 때문이다. 미국 Sandia National Lab의 연구결과에 의하면 사람이 20분만 모니터를 보고 있어도 집중력과 판단력이 떨어진다고 한다.