Chih-Yung Chang

Obstacle-Resistant Deployment Algorithms for Wireless Sensor Networks

Node deployment is an important issue in wireless sensor networks (WSNs). Sensor nodes should be efficiently deployed in a predetermined region in a low-cost and high-coverage-quality manner. Random deployment is the simplest way to deploy sensor nodes but may cause unbalanced deployment and, therefore, increase hardware costs and create coverage holes. This paper presents the efficient obstacle-resistant robot deployment (ORRD) algorithm, which involves the design of a node placement policy, a serpentine movement policy, obstacle-handling rules, and boundary rules. By applying the proposed ORRD, the robot rapidly deploys a near-minimal number of sensor nodes to achieve full sensing coverage, even though there exist unpredicted obstacles with regular or irregular shapes. Performance results reveal that ORRD outperforms the existing robot deployment mechanism in terms of power conservation and obstacle resistance and, therefore, achieves better deployment performance.

Energy-aware node placement, topology control and MAC scheduling for wireless sensor networks

In the WSNs, the nodes closer to the sink node have heavier traffic load for packet forwarding because they do not only collect data within their sensing range but also relay data for nodes further away. The unbalanced power consumption among sensor nodes may cause network partition. This paper proposes efficient node placement, topology control, and MAC scheduling protocols to prolong the sensor network lifetime, balance the power consumption of sensor nodes, and avoid collision. Firstly, a virtual tree topology is constructed based on Grid-based WSNs. Then two node-placement techniques, namely Distance-based and Density-based deployment schemes, are proposed to balance the power consumption of sensor nodes. Finally, a collision-free MAC scheduling protocol is proposed to prevent the packet transmissions from collision. In addition, extension of the proposed protocols are made from a Grid-based WSN to a randomly deployed WSN, enabling the developed energy-balanced schemes to be generally applied to randomly deployed WSNs. Simulation results reveal that the developed protocols can efficiently balance each sensor nodes power consumption and prolong the network lifetime in both Grid-based and randomly deployed WSNs.

Design and implementation of ad hoc classroom and eSchoolbag systems for ubiquitous learning

This paper describes the design and implementation of a learning technology project. The purpose of this project is to develop advanced wireless technologies for building an ad hoc classroom in order to contrive a modern and new learning environment. A wireless platform is developed for teacher and students to establish a classroom dynamically irrespective of location and time bounds. As supported in a traditional classroom, we develop information technology to provide the teacher with teaching aids, such as blackboard, board rubber, colored chalk, microphone, voice recorder, video recorder, and so on, for course teaching and discussions in an ad hoc classroom. In addition, we provide students with an electronic schoolbag (or eSchoolbag) which packs electronic book, notebook, parents contact book, pencil case, writing materials, sheets, calculator, address book, and so on. Taking lessons in a lively, vivid, and new learning environment, students are expected to enhance their learning performance without any burden like attending classes physically. Moreover students get more flexible scope of learning at a convenient time.

An Obstacle-Free and Power-Efficient Deployment Algorithm for Wireless Sensor Networks

This paper proposes a robot-deployment algorithm that overcomes unpredicted obstacles and employs full-coverage deployment with a minimal number of sensor nodes. Without the location information, node placement and spiral movement policies are proposed for the robot to deploy sensors efficiently to achieve power conservation and full coverage, while an obstacle surrounding movement policy is proposed to reduce the impacts of an obstacle upon deployment. Simulation results reveal that the proposed robot-deployment algorithm outperforms most existing robot-deployment mechanisms in power conservation and obstacle resistance and therefore achieves a better deployment performance.

Obstacle-free geocasting protocols for single/multi-destination short message services in ad hoc networks

Mobile ad hoc networks (MANET) comprise mobile hosts in a network bereft of base stations and characterized by a highly dynamic network topology. The MANET environment contains unpredictable obstacles, such as mountains, lakes, buildings, or regions without any hosts, impeding or blocking message relay. This study proposes geocasting protocols for sending short message from a source host to single or multiple geocasting regions in ad hoc networks. The proposed protocols keep messages away from unpredictable obstacles and create a small flooding region. Experimental results show that a source host can send a short message to all hosts located in single or multiple geographical areas with a high success rate and low flooding overhead.

Distributed direction-based localization in wireless sensor networks

Location awareness is an attractive research issue in the wireless sensor network (WSN). However, precise location information may be unavailable due to the constraint in energy, computation, or terrain. Additionally, several applications can tolerate the diverse level of inaccuracy in such geographic information. Thus, this paper presents a direction-based localization scheme, DLS, whose main goal is for each sensor to determine its direction rather than its absolute position. The direction we are concerned with is the one relative to the sink. Motivated by the proposed spatial locality property, DLS considers multiple messages received for a sensor to determine its direction. Furthermore, a novel scheme, anchor deployment strategy, is also proposed for the improvement of the estimated correctness in direction of the sensor within the communication range of the sink. With the aid of the virtual dual direction coordinate (VDDC) system, DLS is able to efficiently and precisely position sensors around the axes. We evaluate DLS via simulations in terms of various numbers of sensors and communication ranges for the scenarios with different numbers of directions. The average correct rates in DLS reach approximately 94%, 86%, and 81% for the networks with 4, 8, and 16 directions, respectively. DLS achieves outstanding performance for the high density networks as well. In addition, DLS also works well regardless of the sink placement. Overall, simulation results validate the practicality of DLS, and show that DLS can effectively achieve direction estimation.

Anchor-Guiding Mechanism for Beacon-Assisted Localization in Wireless Sensor Networks

Localization is one of the most important issues in wireless sensor networks (WSNs). In the most widely proposed range-free algorithms, nodes estimate location by employing the geometric constraints imposed by the location of the mobile anchor. However, none of them addresses how the mobile anchor moves to optimize the improvement of location inaccuracies and minimize the anchors movement. This paper assumes that previous range-free algorithms have been executed for a period of time and the deployed sensors are of different location inaccuracies. According to the size of the estimative region of each static sensor, an anchor-guiding mechanism is proposed to determine the beacon locations and construct an efficient path for the mobile anchor. Experimental study reveals that the proposed anchor-guiding mechanism effectively guides the mobile anchor to move along an efficient path, thereby saving the time required for improving or balancing the location inaccuracies of all sensor nodes.

A Comparative Study on Human Activity Recognition Using Inertial Sensors in a Smartphone

Activity recognition plays an essential role in bridging the gap between the low-level sensor data and the high-level applications in ambient-assisted living systems. With the aim to obtain satisfactory recognition rate and adapt to various application scenarios, a variety of sensors have been exploited, among which, smartphone-embedded inertial sensors are widely applied due to its convenience, low cost, and intrusiveness. In this paper, we explore the power of triaxial accelerometer and gyroscope built-in a smartphone in recognizing human physical activities in situations, where they are used simultaneously or separately. A novel feature selection approach is then proposed in order to select a subset of discriminant features, construct an online activity recognizer with better generalization ability, and reduce the smartphone power consumption. Experimental results on a publicly available data set show that the fusion of both accelerometer and gyroscope data contributes to obtain better recognition performance than that of using single source data, and that the proposed feature selector outperforms three other comparative approaches in terms of four performance measures. In addition, great improvement in time performance can be achieved with an effective feature selector, indicating the way of power saving and its applicability to real-world activity recognition.

Dynamic bandwidth allocation for QoS routing on TDMA-based mobile ad hoc networks

The paper proposes several dynamic bandwidth allocation strategies for QoS routing on TDMA-based mobile ad hoc networks. Comprehensively, these strategies are called a distributed slots reservation protocol (DSRP). In DSRP, QoS routing only depends on one-hop neighboring information of each mobile host (MH). In addition, slot inhibited policies (SIPs) and slot decision policies (SDPs) are proposed to determine which slots are valid to use and which slots in the valid slots can be used actually, respectively. In SDPs, three heuristic policies, 3BDP, LCFP, and MRFP, are proposed to increase the success rate of a QoS route and alleviate the slot shortage problems. Moreover, a slot adjustment protocol (SAP) is proposed for a conflicting MH to coordinate the slot usage of its neighbors during the route reservation phase in order to accommodate more routes in the network. The slot adjustment algorithm (SAA) invoked in SAP is a branch-and-bound algorithm, which is an optimum algorithm in terms of the number of slots to be adjusted, on the premise that not to break down any existing route. QoS route maintenance and improvement are also provided. By the simulation results, the proposed protocol cannot only increase the success rate in search of a route with bandwidth requirement guaranteed but also raise the throughput and efficiency of the network.

Efficient path-based multicast in wormhole-routed mesh networks

The capability of multidestination wormhole allows a message to be propagated along any valid path in a wormhole-routed network conforming to the underlying base routing scheme. The multicast on the path-based routing model is highly dependent on the spatial locality of destinations participating in multicasting. In this paper, we propose two proximity grouping schemes for efficient multicast in wormhole-routed mesh networks with multidestination capability by exploiting the spatial locality of the destination set. The first grouping scheme, graph-based proximity grouping, is proposed to group the destinations together with locality to construct several disjoint sub-meshes. This is achieved by modeling the proximity grouping problem to graph partitioning problem. The second one, pattern-based proximity grouping, is proposed by the pattern classification schemes to achieve the goal of the proximity grouping. By simulation results, we show the routing performance gains over the traditional Hamiltonian-path routing scheme.