Gwo-Jong Yu

A Hierarchical MDS-Based Localization Algorithm for Wireless Sensor Networks

In many applications of wireless sensor networks, location is very important information. Conventional location information comes from manual setting or GPS device. However, manual location setting requires huge cost of human time, and GPS location setting requires expensive device cost and large device size. Furthermore, GPS can not operate in indoor environment. Both approaches are not applicable to localization task of wireless sensor networks. In this paper, an accurate and efficient localization algorithm based on multidimensional scaling (AIDS) is proposed in hierarchical network environment. Through localized computation of multidimensional scaling within a cluster, the computation overhead can be distributed to each cluster. On the other hand, MDS- based localization approach requires the estimation of multihop distance. Through restricting estimation of multihop distances within a cluster, the proposed localization algorithm achieves better accuracy and can operate in non-convex network environment. Experimental results reveal that the proposed HMDS localization algorithm outperforms MDSMAP algorithm in terms of accuracy.

Relay reduction and disjoint routes construction for scatternet over Bluetooth radio system

Bluetooth is a new technology for low-cost, low-power, and short-range wireless communication. By constructing a piconet, Bluetooth device establishes link and communicates with other device in a master-slave manner. Relay is a Bluetooth device that joins two or more piconets and forwards data from one piconet to another, providing multi-hop (or inter-piconet) communication services. In a Bluetooth scatternet, the number of relays and the degree of each relay are factors that significantly affect the performance of entire network. Unnecessary relays raise the difficulty of scheduling, leading to frequent packet loss. Relay switching among several piconets in turns also creates guard time overhead and increases the transmission delay. This study presents an effective protocol that can dynamically adjust the network topology by reducing the unnecessary relays. An efficient scatternet environment thus can be constructed with characteristics of connected, high bandwidth utilization and low maintenance cost. Additionally, a routing protocol is developed to reduce the path length and generate two disjoint routes for any pair of source and destination devices located in different piconets. Experimental results demonstrate that the proposed protocols perform well in terms of route length, bandwidth consumption, and transmission delay.

A framework of mobile context management for supporting context-aware environments in mobile ad hoc networks

In this paper, we propose a framework for supporting context-aware environments in mobile ad hoc networks (MANETs). A virtual overlay network and two novel approaches in this framework are addressed to significantly improve the efficiency of data delivery in MANETs. The surrounding context of mobile nodes is used to determine which scheme, push-based or pull-based approaches, is adopted. When a real-time event happened in a node, push-based approach is adopted to disseminate urgent messages to its neighboring nodes. On the contrary, pull-based approach is adopted by building a virtual backbone, namely segment-tree, for seeking for more contextual information. Finally, the simulation is conducted to illustrate the performance achievements that our methods outperform the existing publish/subscribe approach based on AODV routing protocol.

A content-based image retrieval system for outdoor ecology learning: a firefly watching system

We devote to provide teachers and students with short-range wireless learning environment. The wireless learning platform consists of wireless handheld devices (PDA, notebook, etc.) carried by the guide and learners. A content-based image retrieval system (CBIR) is constructed to provide learner with required information using image recognition and wireless transmission technologies, such that the objective of outdoor ecology learning can be achieved. A firefly database is used as an instance to illustrate the operations of CBIR system. Instead of learning from textbook, a real firefly in natural environment can be observed and learned through digital camera and image recognition system. During the learning activity, the teacher can use this CBIR system to control the learning progress, evaluate the learning effects and provide necessary assistances to students in order to have a flourish learning environment.

An efficient cluster-based multi-channel management protocol for wireless Ad Hoc networks

In Ad Hoc networking, cluster-based communication protocol can reduce large amount of flooding packets in route establishment process. However, the 802.11 medium access control (MAC) protocol is not dedicated to cluster-based network architecture. Applying 802.11 MAC protocol to cluster-based network introduces problems of inefficient channel utilization in announcement traffic indication message (ATIM) and data sub-windows for gateway nodes, heavy channel contention in some channels, large power consumption of mobile hosts, and poor utilization of multi-channel resources. In this paper, we propose a MAC layer multi-channel management protocol which takes power saving issues into consideration in a cluster-based network topology. The proposed protocol aims at effective utilization of multi-channel bandwidth for data communications among mobile hosts. Features of the proposed protocol includes: (1) preserving the property of fair channel contention in original 802.11 protocol, (2) constructing a proper contention condition for mobile hosts, (3) reducing power consumption for idle mobile hosts, (4) reducing probability of collision and unnecessary power consumption due to heavy contention, and (5) decreasing the transmission delay of gateway node through proper management of inter-cluster traffic. Experimental results reveal that the proposed protocol has good performance in network throughputs, average transmission delay time and energy consumption.

An energy-efficient hole-healing mechanism for wireless sensor networks with obstacles

In wireless sensor networks (WSNs), coverage of the monitoring area represents the surveillance quality. Since sensor nodes are battery powered and placed outdoor, there will be failures due to energy exhaustion or environmental influence, resulting in coverage-loss. In literature, a number of studies developed robot repairing algorithms that aim at maintaining full coverage. However, they did not consider the time constraint for network maintenance. Furthermore, they did not consider the existence of obstacles and the constraint of limited energy of the robot. This paper presents a novel tracking mechanism and robot repairing algorithm for maintaining the coverage quality of the given WSN. Without support of location information, the tracking mechanism leaves robot’s footmark on sensors so that they can learn better routes for sending repairing requests to the robot. Upon receiving several repairing request messages, the robot applies the proposed repairing algorithm to establish an efficient route that passes through all failure regions with low overhead in terms of the required time and the power consumption. In addition, the proposed repairing algorithm also considers the remaining energy of the robot so that the robot can move back to home for recharging energy and overcome the unpredicted obstacles. Performance results reveal that the developed protocol can efficiently maintain the coverage quality while the required time and energy consumption are significantly reduced. Copyright

Congestion control of bluetooth radio system by piconet restructuring

Bluetooth is a low-cost and short-range wireless communication technology. Two or more bluetooth devices connected form a piconet and two or more piconets connected form a scatternet through relay devices. Without the consideration of traffic flows, a scatternet may operate with serious congestion problem. Congestion problem can be resolved by either reduced traffic flows or increased bandwidth provision. In bluetooth, new piconet can be dynamically constructed to increase system bandwidth. However, as the number of piconet is increased, collision problem among piconets becomes a serious problem. The objective of this paper is to resolve the congestion problems in a scatternet through piconet restructuring which perform both flow analysis and distributed role-switching technique. Advantages of the proposed piconet restructuring mechanism includes the following: (1) the communication bottleneck can be released; (2) the communication path is shortened; (3) the transmission latency is reduced; and (4) the lifetime of piconets can be increased. Experimental results demonstrated that the proposed method could effectively increase the transmission efficient in each piconet and increase the performance of an entire scatternet.

Path Construction and Visit Scheduling for Targets by Using Data Mules

In this paper, the target patrolling problem was considered, in which a set of mobile data collectors, known as data mules (DMs), must efficiently patrol a given set of targets. Because the time interval (or visiting interval) between consecutive visits to each target reflects the degree to which that target is monitored, the goal of this paper was to balance the visiting interval of each target. This paper first presents the basic target points patrolling algorithm, which enables an efficient patrolling route to be constructed for numerous DMs, such that the visiting intervals of all target points are stable. For scenarios containing weighted target points, a weighted target points patrolling (W-TPP) algorithm is presented, which ensures that targets with higher weights have higher data collection frequencies. The energy constraint of each DM was also considered, and this paper presents a W-TPP with recharge (RW-TPP) algorithm, which treats the energy recharge station as a weighted target and arranges for DMs to visit the recharge station before running out of energy. The performance results demonstrated that the proposed algorithms outperformed existing approaches in average visiting frequency, DM movement distance, average quality of monitoring satisfaction rate, and efficiency index.

Task migration in n -dimensional wormhole-routed mesh multicomputers

In a mesh multicomputer, performing jobs needs to schedule submeshes according to some processor allocation scheme. In order to assign the incoming jobs to a free submesh, a task compaction scheme is needed to generate a larger contiguous free region. The overhead of compaction depends on the efficiency of the task migration scheme. In this paper, two simple task migration schemes are first proposed in n-dimensional mesh multicomputers with supporting dimension-ordered wormhole routing in one-port communication model. Then, a hybrid scheme which combines advantages of the two schemes is discussed. Finally, we evaluate the performance of all of these proposed approaches.

TCWTP: Time-Constrained Weighted Targets Patrolling Mechanism in Wireless Mobile Sensor Networks

Target coverage problems have received much attention in recent years. In a large monitoring environment where targets are distributed over an entire monitored region, deploying static sensors leads to high hardware costs because a high number of sensors may be required to achieve network connectivity. This paper considers the target-patrol issue where a set of mobile data mules (DMs) are dispatched to efficiently patrol the given targets under a predefined time constraint. The targets are assigned weights indicating their importance, where more important targets should be visited more frequently by the DMs. Accordingly, this paper proposes a time-constrained weighted targets patrolling (TCWTP) algorithm for locally constructing efficient patrol paths, thereby ensuring globally stable intervals between visits to all target points. A performance analysis revealed that the proposed TCWTP mechanism outperforms existing works in terms of the average interval between visits, quality of monitoring satisfaction ratio, and monitoring fairness ratio.