Hua-Wen Tsai

Mobile object tracking in wireless sensor networks

Wireless sensor network is an emerging technology that enables remote monitoring objects and environment. This paper proposes a protocol to track a mobile object in a sensor network dynamically. The previous researches almost focus on how to track object accurately and they do not consider the query for mobile sources. Additionally, they need not report the tracking information to user. The work is concentrated on mobile user how to query target tracks and obtain the target position effectively. The mobile user can obtain the tracking object position without broadcast query. The user is moving and approaching the target when he/she knows the targets position. Wireless sensor networks can assist user to detect target as well as keep the movement information of the target. Sensor nodes establish face structure to track the designated target and keep target tracks. The source follows the tracks to approaching target. To chase the object quick and maintain an accurate tracking route, the sensors cooperate together to shorten the route between target and source dynamically. A source can quickly approach a target along a shortened route. Finally, we compare the proposed scheme with three flooding-based query methods. By the simulation results, the proposed protocol has better performance than that of flooding-based query methods.

Geographic convergecast using mobile sink in wireless sensor networks

This paper presents a novel convergecast algorithm called, Virtual Circle Combined Straight Routing (VCCSR), which collects data in a wireless sensor network (WSN) using a mobile sink. Tree-based routing offers the shortest routes to deliver data, and it is a common scheme used by mobile sinks to collect data from sensors. When a mobile sink moves, the routes between the sink and the sensors must be reconstructed dynamically, which wastes a great amount of energy. VCCSR selects a set of cluster heads located near the virtual backbone, and when the sink issues a query in the WSN, a spanning tree is constructed to collect and complete data periodically. With VCCSR, the spanning tree does not need to be reconstructed when the mobile sinks location changes because the algorithm is able to update the location of the mobile sink, which then delivers this information to the cluster heads and adjusts the routing. The goal of the proposed algorithm is to decrease the reconstruction cost and increase the data delivery ratio. In comparing the VCCSR protocol with BFS tree-based protocols in simulation, this paper demonstrates that the spanning tree adjustment process executed by VCCSR does in fact decrease the reconstruction cost and increase the data delivery ratio.

Gathering-Load-Balanced Tree Protocol for Wireless Sensor Networks

Wireless communications and digital electronics have enabled the development of low-power, low-cost, multifunctional sensors. The functionality of sensor network mainly is the measurement collection. The previous proposed protocols mainly focus on broadcasting tree structure, but it may not be efficient in data gathering. In this paper, we propose novel tree architecture that is a dynamic, adjustable, load-balanced tree in sensor networks to decrease the energy utilization and to prolong the lifetime of sensors. A load-balanced tree can share the forwarding loads between non-leaf nodes. Due to the limit of tree topology, we try to adjust forming a tree that has similar amount of children between non-leaf nodes. When the energy of non-leaf node is lower than a designated threshold, the tree structure can be readjusted to prolong the lifetime of tree. In simulation, we compare our protocol with different adjustment phases and an existed protocol. From the result, our protocol can have better performance than others

Adjustable convergecast tree protocol for wireless sensor networks

For data-collection applications in sensor networks, it is important to ensure base station receives a complete picture about the monitored area. Convergecast is an important communication pattern commonly used to collect continuous data. The prior broadcast trees are not suitable for convergecast, because convergecast is a reverse broadcast process. We point out the load-balancing problem in the current design of sensor networks. A non-load-balancing tree makes some nodes consume energy faster than others. It is important to design a distributed load-balancing solution due to the lack of global knowledge about the network topology. This paper presents a novel convergecast tree protocol and a distributed adjustment algorithm to attain load balancing and to extend network lifetime. The tree protocol constructs an approximate load-balancing convergecast tree. Additionally, the adjustment algorithm dynamically adjusts tree structure to avoid breaking tree link. The tree adjustment only needs localized information and operations at the sensors. Moreover, the tree adjustment is controlled by a sensors grandparent to avoid loop problem. This study performs extensive simulations, demonstrating that the proposed protocols can effectively increase convergecast throughput.

Service Discovery in Mobile Ad Hoc Networks Based on Grid

Service discovery is a crucial operation for the usability of mobile ad hoc networks (MANETs). Traditional solutions to service discovery that were adopted on the Internet are not well suited for MANETs because of their dynamic nature. This paper presents a novel service discovery protocol based on a hierarchical grid architecture in an ad hoc network. The geographical area of a MANET is divided into a 2-D logical hierarchical grid. The proposed scheme registers the information of available services to a specific location along a predefined trajectory. To enhance resource availability and effective discovery, each grid cell selects a directory for caching available services. This paper utilizes the transmitting trajectory to improve the efficiency of registration and discovery. First, the service provider registers a service along the proposed register trajectory. The requestor then discovers the service along the discovery trajectory to acquire the service information. This paper also proposes an improved process to avoid the sparse node network topology. This paper adopts analysis and simulation to measure the protocol performance. The analytical and simulation results show that the proposed protocol can raise the discovery success ratio and reduce the discovery cost more than the existing geographical service discovery protocol.

Dynamic object tracking in wireless sensor networks

In this paper, we propose a protocol for dynamically tracking a mobile object in a sensor network. The problem we discussed here is that one source object is set to track a mobile object, called a target, in a wireless sensor network. The source is moving to approach the target. In this kind of object tracking sensor networks, the activated sensor nodes can detect an object to be tracked as well as to keep tracking of information for the source. The source follows the movement route to approach the sensor node which the object is covered in. In order to maintain the accurate route, the sensors can be worked together to dynamically adjust the route between the target and source. The source moves to reach the site of the object quickly along the adjusted route in a power saving way. Finally, we compare our scheme with others with flooding-based mechanism.

Object coverage with camera rotation in visual sensor networks

This paper is to study the object coverage problem in visual sensor networks. When sensors equipped camera with rotating capability in the monitoring environment are deployed randomly, the images of target object with circle shape may be captured by different camera nodes in different orientations at the same time. In order to achieve the full coverage of an object, there might be lots of redundant image data to consume the transmission energy in visual sensor networks. An approach is proposed to reduce the cover set of camera nodes by rotating cameras of sensors. Such a set can cover the entire object using as few sensors as possible. In addition, a mapping is proposed for find out the coverage problem for target objects with convex polygon shape. The simulation results show that our approach can reduce the number of sensors while preserving the maximum coverage range of object.

Minimal Time and Conflict-Free Schedule for Convergecast in Wireless Sensor Networks

A time division multiple access (TDMA) scheduling technique, which solves collision problem and collects a complete data efficiently, is adopted to assign communication mission into the available time slots. This paper proposes a novel conflict-free convergecast scheduling method to minimize the collecting time in a wireless sensor network. The proposed method first constructs a tree structure in the sensor network and utilizes the tree information to schedule a conflict-free convergecast. The simulated results show that the proposed method can diminish the required timeslots efficiently and achieve a conflict-free convergecast. The contributions of the work are to accelerate the speed of data collection, collect the complete data from the sensor network, reduce the energy consumption of sensors and prolong the network lifetime.

Data Aggregation for Range Query in Wireless Sensor Networks

This work proposes efficient data aggregation algorithms based on a virtual grid for range query in wireless sensor networks. A sensor node is selected to be a manager, called head, in each grid. The responsibilities of head are to detect generated event, announce to all other heads, and respond to a moving user. A user obtains the occurred event information from its grid head. If a user is interested in an event, it issues a query to acquire data from a specified regular-shape or spreading irregular-shape ranges. Users can oversee the spreading event via querying the incurred irregular-shape range. In addition, this work proposes efficient approaches to gather data from sensor networks while voids exist. Finally, experimental results show that the proposed approaches are more energy-efficiency than the existing approach.

An on-demand routing protocol with backtracking for mobile ad hoc networks

A mobile ad hoc network (MANET) is characterized by multihop wireless links in the absence of cellular infrastructure and frequent host mobility. In this paper, a new on-demand routing protocol is proposed, named on-demand routing protocol with backtracking (ORB), for multihop mobile ad hoc networks. Suppose a source host wants to deliver a message to a destination in a MANET. First, the source host issues a request to search the destination. When a node receives the request packet, it gets a hop count value which can point the way to the source. This node broadcasts the request packet to its neighbors. When a destination receives this request, it issues a reply back to the source. We proposed a scoped flooding approach which is applied to reply information to the source. This approach will find out multipath from a source to a destination Every node in the MANET maintains some information for this source-destination pair in its own route table. Each node in the forwarding route uses this information to select a group of nodes, named checkpoint nodes, which may have multipath maintained to that destination. The checkpoint node characteristic is such that a route can be recovered instantly without the need for extra control packets. When a delivering node is aware that the forwarding route is broken, it transmits an error packet back to the source along the return path. When a checkpoint receives the error packet that is backtracked to the source, it has backup paths to recover the broken route. This new route can be used immediately The main advantage of our ORB is to reduce the flooding search time and cost when a route has been broken. We show that the proposed scheme outperforms the on-demand routing protocol existing in mobile ad hoc networks.