C. Suh and Y.-B. Ko: Design and Implementation of Intelligent Home Control Systems based on Active Sensor Networks

Contributed Paper Manuscript received July 7, 2008 0098 3063/08/$20.00 © 2008 IEEE

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Design and Implementation of Intelligent Home Control Systems

based on Active Sensor Networks Changsu Suh and Young-Bae Ko, Member, IEEE

Abstract —The ubiquitous home network has gained wide-

spread attentions due to its seamless integration into everyday life. This innovative system transparently unifies various home appliances, smart sensors/actuators and wireless communication technologies. The ubiquitous home network gradually forms a complex system to process various tasks. Developing this trend, we suggest a new intelligent home control system based on a wireless sensor/actuator network (we call it as an “Active sensor network”). The proposed intelligent home control system divides and assigns various home network tasks to appropriate components. It can integrate diversified physical sensing information and control various consumer home devices, with the support of active sensor networks having both sensor and actuator components. We develop a new routing protocol LQIR (Link Quality Indicator based Routing) to improve the performance of our active sensor networks. This paper introduces the proposed home control system’s design that provides intelligent services for users. We demonstrate its implementation using a real testbed.1 Index Terms — Ubiquitous home networks, Intelligent home control systems, Active sensor networks

I. INTRODUCTION Recent progress in low-powered micro device designs and

wireless communication technologies enables the Ubiquitous Computing paradigm [1] to become a reality. This paradigm promises to provide adaptive information and services to users anywhere anytime using various devices. Numerous applications have been proposed in different domains of our everyday life such as in homes, offices, streets, buildings and shops. Ubiquitous computing in the home domain can be distributed in different scales throughout our daily lives. Developing killer applications and services for ubiquitous home will confer important commercial value. A number of projects and research [3]-[9] have developed

ubiquitous home network applications. Compared to traditional home networks, the in-progress ubiquitous home network collects user activity patterns, as well as physical

1 Changsu Suh was with the Graduate School of Information & Computer

Engineering, Ajou University. Now he is with the R&D department of Hanback Electronics, Daejeon, Korea (e-mail: scs@ajou.ac.kr)

Young-Bae Ko is an associate professor in the School of Information & Computer Engineering, Ajou University, Korea (e-mail: youngko@ajou.ac.kr)

sensing information on the surrounding environment, to support more intelligent and adaptive home services. It has the potential to control consumer home devices used in everyday life. Eventually, users will experience the convenience of performing ordinary activities and increased satisfaction offered by adaptive home services. Several conditions are required to reap advantages from the

ubiquitous home network. For instance, computing systems should integrate diversified sensing information to perceive the current situation in the home area. Also, they should be able to control various consumer home devices. The home system may become complex, as the number of sensors and devices offered increases. Therefore, home network systems should be designed distributing various tasks into proper computational units to reduce complexity. In this work, we design an intelligent home control system

that can assign tasks to suitable components. Using a wireless sensor network with actuator functionality [2], our system can automatically gather physical sensing information and efficiently control various consumer home devices. We call this network the Active sensor network. The system can efficiently distribute various tasks related to home network to corresponding components and implement real ubiquitous home services via smart sensors and actuators deployed in home areas. Fig. 1 gives an overview of the proposed intelligent home

control system. The system, being supported by underlying active sensor networks (i.e., wireless sensor/actuator networks) and additional wired/wireless communications technologies, can control consumer home devices such as lamps, gas valves, curtains, TVs, and air conditioners. It also interoperates with various mobile devices, such as PDA and mobile phones, using IEEE 802.11/802.3, RFID and CDMA technology. Our intelligent home control system based on active sensor

networks consists of various software components as follows. Service Components: These components represent some

ubiquitous home services provided by our system. Examples include services for home automation, home security and home management.

Decision Component: The component recognizes the current home environment via active sensor networks, and enables the service components to select the appropriate service.

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Sensing Component: The component gathers sensing data and special event information from the active sensor networking infrastructure deployed in home environments. This sensing component provides this information to the decision component. The decision component then adaptively selects the correct home services based on the current home state of affairs.

Control Component: The component instructs special control commands to the deployed actuators, such as relay switches or Infra-Reds. These provide methods to control and handle various consumer home devices such as lamps, gas valves, TVs and air conditioners.

Interaction Component: The component manages interaction between our home control system (i.e., the control component) behind a sink node and the active sensor networks deployed in a home domain.

Additional Communication Components: These components manage some other networking technologies (beyond the active sensor networks), such as WLAN, Ethernet, RFID and CDMA. These technologies leverage our provided home services to become more effective.

This paper details our proposed system and its

implementation. The contributions of our work are as follows: First, we propose a more intelligent home control system based on active sensor networks and design it to be more flexible with a software component-based approach. Second, we develop a novel sensor routing protocol to gain adaptive control of smart sensors and actuators. Third, we implement hardware and software utilized in our system. Fourth, we show how real ubiquitous home scenarios operate and are implemented successfully in our system.

II. RELATED WORK In this section, we briefly survey the existing works for

intelligent home network systems and, based on their main contributions, try to classify them into three types: Decision Support oriented, Service Provision oriented and Real Implementation oriented.

First, some work has focused on how to make the decisions for the home networks more efficiently. For example, the MavHome project [3] focused on the design of intelligent agents and the role of prediction algorithms, based on the inhabitants’ repetitive actions to automatically provide adaptive home services. The Aware Home project [4] deals with decisions about the inhabitants’ location and activity recognition within a house, utilizing multi-camera tracking, audio/video sensors and automated separation of sound sources.

Secondly, the research effort for providing more convenient and intelligent services for home environments has also been conducted. Sival et al.[5] utilized pressure-based floor sensors to achieve efficient retrieval and summarization of video and audio data. When a pressure-based floor sensor detects the person's movement, the information is analyzed to index the video and audio data. This demonstrates efficient multimedia services for the human movement patterns. Bae et al.[6] proposed TV-oriented architecture to manage data broadcasting services, based on a common application platform middleware. Stankovic et al.[7] presented challenging issues for the provision of healthcare services in the home arena.

Last, more practical research to emphasize a real implementation has been done as well. Mori et al.[8] suggested a ubiquitous sensing room equipped with cameras,

Fig. 1 Overview of the Proposed Intelligent Home Control System based on Active Sensor Networks

C. Suh and Y.-B. Ko: Design and Implementation of Intelligent Home Control Systems based on Active Sensor Networks 1179

various sensors and RFID to measure natural daily human behavior. Yamazaki[9] built the ubiquitous home as a real test-bed. It is equipped with several cameras, microphones, RFID and sensors. The author suggested a new database system and communication middleware for home management.

Compared to existing work, this paper focuses on the so-called active sensor network-based home control system to efficiently distribute home control tasks to appropriate components and automatically manage consumer home devices. It makes home network’s configuration and management more convenient and comfortable. Consumer home devices have self-configuration and self-organization features using smart sensors or actuators. We have implemented the ubiquitous home services based on our proposed system with various home appliances, smart nodes and communication technologies.

III. ACTIVE SENSOR NETWORK ARCHITECTURE In this section, we address the active sensor network

architecture utilized in the proposed home control system. Our active sensor network consists of a number of smart nodes (i.e., sensors and actuators). They may proffer several tasks, such as gathering physical home environment information and controlling various consumer home devices. Although these two types of smart nodes have different functionalities, they both have the computation and RF communication abilities to automatically establish wireless networks. We discuss these smart sensors and actuators in more detail below. We design the Interaction Component and new routing

protocol to interact with our control home system and automatically establish networks. In the following subsections, we describe how smart devices can interact with and be controlled by our home system, and how they can form multi-hop networks wirelessly.

A. Smart Sensors and Actuators We have developed the smart sensor nodes that are classified

into two different types of a generic sensor and an actuator. Generic sensor typed nodes try either to detect the general physical sensing measurements such as temperature, humidity and light or check for the special events such as gas leaks, human movement and window status detection. Whereas, actuator typed nodes can directly control consumer home devices. In our system, some actuators are deployed near the consumer home devices and connected to their electronic switch by the relay switch module (which is also developed by ourselves). The control ability of actuator is limited to turn on/off actions, because the relay switch module simply works as an electronic switch. Our actuator typed node utilizes IR (Infra-Red) communication also in order to instruct complex consumer devices such as TV, Air Conditioners and Air Cleaners. This collaboration among actuator nodes and

consumer home devices leads an extension beyond traditional wireless sensor networks. Our active sensor network can collect diversified sensing information and control various consumer home devices. The generic sensor and actuator nodes are managed by the Sensing Component and Control Component, respectively.

B. Interaction Component Each smart node should have a special computational entry,

which can understand commands transmitted from the home system and recognize its tasks according to its sensing or actuator functionality, to interact with our home system. We develop the Interaction Component on smart nodes as a part of our system for this purpose. Since each node is equipped with special capabilities such as gas detection, relay switching and IR controlling, each node may perform different actions according to its capabilities. Our Interaction Component is design to distinguish these different capabilities and perform adaptive operations. It can respond with appropriate responses to commands transmitted from the home control system.

C. LQIR – Link Quality Indicator based Routing Protocol Each node should have multi-hop routing protocol to

automatically establish the wireless network between smart nodes. We develop a new tree-based routing protocol named as “LQIR (Link Quality Indicator based Routing)”. Conventional routing protocols, such as the one in [10], are difficult to accommodate to dynamic topology variations and to interact with our home control system. We design a new routing protocol specifically for home networks. Our proposed protocol establishes the wireless network, based on the LQI value measured from the RF radio. This idea of using LQI value for the routing purpose has been presented in the ZigBee WPAN standard as well, but it is different from our LQIR protocol in that an on-demand approach is utilized there to make a routing path and hence many control packets are often required. The proposed tree-based LQIR works as follows. When forwarding the data packet to the sink, the

Fig. 2 An example of Active Sensor Network Topology Snapshot

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node selects the special node having the best LQI value among neighbors. The routing topology is adjusted dynamically, since nodes check neighbors’ LQI lists whenever transmitting data. Users can easily see the sensor network topology established in the home, since each packet contains its forwarded routing path list in the packet header. Using this routing path list our home system can discern the routing path from the system to each smart node.

We utilize the B-MAC [11] protocol for shared media access, and a special narrow-band RF device that supports the LQI value, based on the IEEE 802.15.4 standard [12]. We also develop a new topology viewer program to show the established smart nodes’ topology in our home system. Fig. 2 illustrates a snapshot of active sensor networks, captured by using our topology viewer program.

IV. THE PROPOSED HOME CONTROL SYSTEM Our proposed system initially instructs some intentional

commands to smart nodes. It then receives the physical sensing data of interest, or a special event from the corresponding sensors. These operations are managed by Sensing Component, and the gathered information is forwarded to Decision Component. Decision Component can select the adaptive home service based on these detected physical sensing data and special events. The selected services are operated with the help of Control Component and Additional Communication Components according to the predefined scenarios in Service Components. Fig. 3 shows the component architecture in our proposed home control system. In this section, we detail each component’s operations.

A. Sensing Component The Sensing Component is designed to receive and request

the physical sensing data and specific events of interest from

smart nodes. This component manages the generic sensor nodes in the active sensor network. Our home system handles three packet types: Set-Command packet, Data packet and Event packet. The Set-Command packet is generated either to request the physical sensing data of interest or to configure the special event to the generic sensor type nodes. The packet includes the specific sensor device ID and its requested attributes. The packet is transmitted from the Sensing Component to the smart node’s Interaction Component. The Data packet includes the general physical sensing information such as temperature, humidity and light. This information is the response to the Set-Command packet generated from the Sensing Component. The Event packet informs about specific events, such as detecting a person’s presence, locking the door and detecting the presence of dangerous gases. This packet is configured by the Set-Command packet that includes descriptions of the specific event as attributes. Both Data and Event packets are forwarded from the Interaction Component on the smart node to the Sensing Component based on our LQIR protocol.

B. Decision Component Appropriate home services are selected by the Decision

Component, based on the physical sensing information and events gathered by active sensor networks. The Decision Component is provided the Command Request and Data/Event Response interfaces by the Sensing Component. As shown in Fig. 3, it consists of Init Decision part and Service Decision part. The “Init Decision part” is the sum of initial process entries configured by householders. When a householder selects an initial process entry, the selected entry generates appropriate Set-Command packets to the active sensor networks though Command Request interfaces. The corresponding smart node’s Interaction Component may return the appropriate Data packet or Event packet to the home control system to respond to the commands. These response packets are forwarded to the “Service Decision part” through the Data/Event Response interface. The Service Decision part receives the physical sensing information and events detected in the current home areas without additional operations. Service Decision part recognizes the current situation, and executes the adaptive home service from Service Components. For example, if the householder selects the initial process entry for the gas monitoring service in Init Decision part, the matched entry generates the Set-Command packet to receive the current gas level from gas sensors. The command packet is forwarded to active sensor networks through the Command Request interface, and the corresponding gas sensor nodes periodically transmit the Data packet including the detected gas level in the house. The Service Decision part performs the gas monitoring service from the Service Components based on the packets forwarded by the Data/Event Response interface.

Sensing Component

Additional Communication

Components

Active Sensor Networks

Control Component

Service Components

For Services

WLAN/Ethernet/RFID/CDMA

...

Decision Component

Interaction Component

Light

Service Decision

Init Decision

...

Init process entry 1

Data/Event Response Interface

Command Request Interface

Control Request Interface

For Decision

Interaction Component

Gas

Interaction Component

Infra-Red

Interaction Component

Relay Switch

Fig. 3 A Block Diagram for The Component-based Architecture.

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C. Control Component Our system can elaborately command and control most

consumer home devices, based on the actuator nodes. The Control Component manages these actuator nodes. If a home service selected by Decision Component needs to control the special consumer home device, the corresponding service component requests an appropriate device type and its actions to Control Component through the Control Request interface. On receiving the request from the service component, Control Component searches the special smart node ID to control the corresponding home device. It inserts the searched node ID, its routing path and attributes of interest to the Control-Command packets. The Control-Command packet is a special command to control home device in actuator nodes. It includes descriptions about the consumer device type and its actions as attributes. Thus, the packet is forwarded the special actuator type node, based on our LQIR protocol, and the device is controlled according to the intentions of the service component. In our home control system, all tasks, related to controlling consumer home devices, are handled by Control Component.

D. Additional Communication Components Our system requires various communication technologies

to interact with the Internet, Mobile Phone and laptop. These additional communication technologies are managed by the Additional Communication Components.

In aspects of our implementations, current Additional Communication Components are constructed by IEEE 802.3, IEEE 802.11, 13.56MHz RFID and CDMA technologies through the corresponding network devices. IEEE 802.3 (Ethernet) acts as a bridge between Internet and the home system, so that the system can provide HTML web page browsing services. Users can check their current home environment using the web browser anywhere anytime. Since the wireless AP (802.11 WLAN) is also connected to our system, users can access with the home HTTP server through a laptop and PDA in the house. Itinerant users can receive our home services via mobile devices. We have developed a special 15.36MHz RFID reader for our home control system to support RFID applications. It can communicate with ISO 15693 and 14443A RFID tags simultaneously. Any 15.36MHz RFID tag can be identified by our system. We equip the CDMA modem to our home system to support SMS service and voice communications with mobile phones. The home control system connects with wired image cameras to continuously capture images utilized in home services.

E. Service Components One of the goals in this paper is to propose the new

ubiquitous home services that offer inhabitants more comfortable environments to perform day-to-day tasks. The

Service Components include these home services. The Decision Component selects an adaptive service, and it may be performed using Control Component and Additional Communication Components according to the predefined scenarios.

We have designed and implemented seven different kinds of intelligent home services on our proposed system. These services are classified into three types: first, home automation services controlling air conditioners, air cleaners and curtain movements, according to the weather. The second, home security services, detects potential crimes and prevents gas explosions. The last is the home management services via the Internet. More details on these service operations are discussed in the next section.

V. OUR IMPLEMENTATION DETAILS To show the feasibility of the proposed architecture, we

implement our home control system and active sensor networks with various consumer home devices in a house. We developed all the related hardware and software for our system. In this section, we present the potential ubiquitous home services provided by our system.

A. Sensor/Actuator Node Implementation We have developed a smart node that has sensing,

processing and networking abilities. It is equipped with a low power microprocessor and a narrow-band RF device that can support physical-layer functionalities of IEEE 802.15.4 [12]. It is 40mm x 70mm in size, powered by two 1.5V AA batteries. Three type sensors are included in the smart node: light, temperature and humidity sensors. Our smart node has a 50 pin connector that is directly matched to the microprocessor to add additional hardware. Various optional sensor and actuator modules can be equipped with our smart node via this 50 pin connector.

To collect diversified sensing information and control consumer home devices, we developed the several additional optional modules equipped with our smart node. They are connected to the 50 pin connector and are directly controlled by the microprocessor in our smart node. Using the additional modules, the smart node is divided to the generic sensor and actuator nodes. The advanced sensing modules are weather, bio, gas and motion detection sensors that can measure the pressure, the accelerated velocity, the pulse rates, the body heat, a gas leak and the motion, respectively. The actuator modules are Infra-Red and relay modules. The Infra-Red module supports IR communication that can control TV, DVD and air conditioners. The relay modules can switch power on/off in electronic devices and control a motor. These actuator modules enable the role of smart nodes to be changed from just a physical information detector to an electronic device controller. These options boards are managed by our OS-level libraries. Fig. 4 shows our smart node and its options modules.

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B. Sensor/Actuator Functions and Real Deployment Scenarios In this subsection, we describe the deployment of smart

nodes and their possible operation in the home. Fig. 5 shows some of the pictures of the deployment in our implementations. The following list details their functions.

Detecting gas: A gas sensor is deployed near the gas valve to prevent a gas explosion. It periodically checks the gas in the atmosphere and reports the values to the home control system.

Locking gas valves: On detecting a large amount of gas, the gas sensor should immediately issue the instruction to turn off the gas valve. Recall that, one smart actuator, with a relay switch module, is connected to the gas valve.

Detecting human movement: PRI sensors are used to detect human movement. This information can be utilized for intrusion detection. For example, while inhabitants are out of the home, if an unexpected movement occurs, motion is detected by the movement detector sensors; this event is then forwarded to the home control system.

Detecting window status: The magnetic reed switch is equipped with the window boundary to detect its status. When a window is suddenly opened by some intruder, the reed switch sensor can recognize this and inform the home control system of the event.

Curtain movements: The home control system can transmit special Control-Command packets to open or close curtains. A smart actuator is deployed near the curtain and its relay switch module is connected to the motor linked to move curtains.

Control lamp brightness: The sensor node can control illumination of the lamps via the relay switch module. The home system can control home lighting in accord with the

polices based on light sensing information and current time information.

General sensing information: All smart nodes are designed to have light, temperature and humidity sensors. The home control system can gather such information from all home areas where smart nodes are deployed.

C. Description of Intelligent Home Control Services In this subsection, we introduce several ubiquitous home

service scenarios. These scenarios are implemented based on our proposed home networks. Fig. 6 depicts our home services (in part). RFID based door-lock service: Our system utilizes a

RFID card and RFID reader located near the door, instead of a key, to confirm the person’s identification. The home control system decides whether or not to open the door based on the TAG ID in the RFID card of visitor. Upon deciding to open the door, the system transmits the corresponding Control-Command to the actuator node on the door lock device.

Crime Detection: Movement detection sensors and image cameras can be utilized to detect crimes. If an unexpected moving event is checked by the PRI sensor when inhabitants are absent from the home, the information is forwarded to the home control system. The home control system informs the inhabitants and security provider via CDMA modem. The system can also command the installed wired cameras to capture the intruders’ images.

Fig. 4 Our Smart Node and its Options Modules

Fig. 5 Selected Pictures of Sensor/Actuator Nodes in Real House

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These pictures are uploaded to the web-server, so inhabitants can see from anywhere.

IR communication service via Internet: Infra-red (IR) device can support IR communication with complex consumer home devices. TV, DVD, air conditioner and air cleaner can be controlled by our system. Our home control system provides controlling methods of the Infra-Red sensors using the HTTP server. The user can control these home devices using the web browser via Internet.

Talking service with visitors when nobody in home: In some cases, friends and family may visit the home while the resident is absent. The visitor activate the doorbell, the doorbell event is generated in the active sensor network. Our home control system automatically supports a connection between inhabitant and visitors through the CDMA modem. The user can communicate using a cellular phone, and visitors also respond using a mike and speaker in the door.

Automatic control of air conditioner and air-cleaner service: The home control system can deduce the proximate atmospheric conditions in the house using temperature, humidity and pressure information from sensor nodes. The home control server can adaptively control the air conditioner and air cleaner using the Infra-Red node.

Automatic curtain control service: If it is cold or dark, the home control system decides that closing the curtains is better for the inhabitants. Otherwise the curtains are opened or closed according to the time of day (morning or night). The system can adaptively close or open the curtain with appropriate Control-Command packets.

Gas detecting service: The gas sensor periodically checks gas in the atmosphere and reports the values to our home system to prevent gas explosion. On detecting a large amount of gas, the gas sensor immediately instructs the gas valve actuator node to turn off the valve using its relay switch module. In this situation, there is no latent time to exchange commands with the home control system. The gas sensor autonomously operates, and later informs the home control system.

V. CONCLUSION Ubiquitous home networks excite new possibilities. We address a new intelligent home control system based on active sensor networks to make home networks more intelligent and automatic. We implement the proposed system and develop related hardware and software. We suggest new ubiquitous home scenarios based on the proposed system. We expect that our work contributes towards the development of ubiquitous home networks. As a part of future work, we will apply IEEE 802.15.4a [13] standard technology in our home network systems to support location services.

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Fig.6 Pictures of our Ubiquitous Home Scenario Implementations

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Laboratory for Ubiquitous Computing Research," Lecture Notes in Computer Science, vol. 1670, pp. 191-198, 1999. [5] G. C. de Silva, B. Oh, T. Yamasaki and K. Aizawa, "Ubiquitous Home: Retrieval of Experiences in a Home Environment," IEICE Transactions on Information and Systems, vol. E91-D, no. 2, pp. 330-340, 2008. [6] Yu-S. Bae, B.-J. Oh, K.-D. Moon and S.-W. Kim, "Architecture for Interoperability of Services between an ACAP Receiver and Home Networked Devices," IEEE Transactions on Consumer Electronics, vol. 52, no. 1, pp. 123- 128. 2006 [7] J. Stankovic, Q. Cao, T. Doan, L. Fang, Z. He, R. Kiran, S. Lin, S. Son, R. Stoleru and A. Wood, "Wireless Sensor Networks for In-Home Healthcare: Potential and Challenges," Proc. of the Workshop on High Confidence Medical Devices Software and Systems, June 2005. [8] T. Mori, H. Noguchi, A. Takada and T. Sato, "Sensing Room: Distributed Sensor Environment for Measurement of Human Daily Behavior," Proc. of the International Conference on Networked Sensing Systems, June 2004. [9] T. Yamazaki, "Ubiquitous Home," International Journal of Smart Home, vol. 1, no. 1, pp. 17-22, 2007 [10] J. Hill, R. Szewczyk, A. Woo, S. Hollar, D. Culler, and K. Pister, "System architecture directions for network sensors," Proc. of the International Conference on Architectural Support for Programming Languages and Operating Systems, November 2000. [11] J. Polastre, J. Hill, and D. Culler, "Versatile Low Power Media Access for Wireless Sensor Networks," Proc. of the ACM Conference on Embedded Networked Sensor Systems, November 2004. [12] IEEE Computer Society, MAC and PHY Specifications for Low-Rate Wireless Personal Area Networks (LR-WPANs), IEEE 802.15.4 TM-2003. [13] IEEE Computer Society, Low-Rate Alternative PHY Task Group of IEEE 802.15.4 (TG4a) for the ranging and location, IEEE 802.15.4a-2007.

Changsu Suh received the B.S. and M.S. degree in Information and Communication Engineering from the Ajou University, South Korea in 2004 and 2006, respectively. He is recipient of awards for his academic achievement. His interest is in the research areas of Wireless Sensor Networks, Home networks, IEEE 802.11/802.15.4 MAC protocols, ZigBee networks and implementation of real sensor platforms. E-mail: scs@ajou.ac.kr.

Young-Bae Ko is currently an Associate Professor in the School of Information and Computer Engineering at Ajou University, Korea, leading the Ubiquitous Networked Systems (UbiNeS) Laboratory. Prior to joining Ajou University in 2002, he was with the IBM T. J. Watson Research Center, Hawthorne, New York, as a research staff member in the Department of Ubiquitous Networking and Security. He received his Ph.D. degree in computer science from Texas A&M

University, and B.S. and M.B.A. degrees from Ajou University. His research interests are in the areas of mobile computing and wireless networking. In particular, he is working on mobile ad hoc networks, wireless mesh/sensor networks, and various ubiquitous networked system issues. He was the recipient of a Best Paper award from ACM Mobicom 1998. He has served on the program committees of several conferences and workshops. He also serves on the editorial board of ACM Mobile Computing and Communications Review. See http://uns.ajou.ac.kr for further details.