Chih-Yu Lin

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.

Enabling Cyber Physical Systems with Wireless Sensor Networking Technologies

Over the last few years, we have witnessed a growing interest in cyber physical systems (CPSs) that rely on a strong synergy between computational and physical components. CPSs are expected to have a tremendous impact on many critical sectors (such as energy, manufacturing, healthcare, transportation, and aerospace) of the economy. CPSs have the ability to transform the way human-to-human, human-to-object, and object-to-object interactions take place in the physical and virtual worlds. The increasing pervasiveness of wireless sensor networking (WSN) technologies in many applications makes them an important component of emerging CPS designs. We present some of the most important design requirements of CPS architectures. We discuss key sensor network characteristics that can be leveraged in CPS designs. In addition, we also review a few well-known CPS application domains that depend on WSNs in their design architectures and implementations. Finally, we present some of the challenges that still need to be addressed to enable seamless integration of WSN with CPS designs.

EBDC: An Energy-Balanced Data Collection Mechanism Using a Mobile Data Collector in WSNs

The data collection problem is one of the most important issues in Wireless Sensor Networks (WSNs). Constructing a tree from all sensor nodes to the sink node is the simplest way, but this raises the problem of energy unbalance since the sensors closer to the sink node would have much higher workloads from relaying data. To cope with the energy unbalance problem, a number of mobile-sink mechanisms have been proposed in recent years. This paper proposes an Energy-Balanced Data Collection mechanism, called EBDC, which determines the trajectory of a mobile data collector (or mobile sink) such that the data-relaying workloads of all sensors can be totally balanced. Theoretical analysis and performance evaluation reveal that the proposed EBDC mechanism outperforms the existing approaches in terms of network lifetime and the degree of energy balancing.

Tone-Based Localization for Distinguishing Relative Locations in Wireless Sensor Networks

Bounding-box mechanism is a well-known low-cost localization approach for wireless sensor networks. However, the bounding-box location information cannot distinguish the relative locations of neighboring sensors, hence leading to a poor performance for some applications such as location-aware routing. This paper proposes a Differentiating Relative Locations (DRL) mechanism which uses a mobile anchor to broadcast tones and beacons aiming at distinguishing the relative locations of any two neighboring nodes. With the order of entering and leaving tone transmission range, each sensor is able to identify its relative location relation with each of its neighbors. In addition, two path planning mechanisms are proposed to guarantee that all sensors can identify their relative locations while the energy consumption of the mobile anchor can be effective. Theoretical analysis is developed to estimate the impacts of duty time of tone signals in terms of energy conservation and accuracy of relative locations. Experimental study reveals that the proposed mechanism effectively distinguishes relative locations of any two neighboring nodes and hence significantly improves the performance of location-aware routing in wireless sensor networks (WSNs).

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

Energy-balanced hole-movement mechanism for temporal full-coverage in mobile WSNs

In wireless mobile sensor networks, spatial full-coverage only can be achieved when the surplus mobile sensors contribute a larger coverage area than the hole size. The temporal full coverage problem asks to monitor every point of a given monitoring region within a specific time interval. This paper considers a mobile WSN that contains holes but exists no redundant mobile sensor to heal the hole. To achieve the temporal full-coverage purpose, a distributed hole-movement mechanism is proposed to balance the energy consumptions of mobile sensors. Simulation study reveals that the proposed hole-movement mechanism enhances the coverage ratio of WSN and balance the energy consumption of mobile sensor nodes.

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.

Patrolling Mechanisms for Disconnected Targets in Wireless Mobile Data Mules Networks

This paper considers the target patrolling problem which asks a set of mobile data mules to efficiently patrol a set of given targets. Since the time interval (also referred to visiting interval) for consecutively visiting to each target reflects the monitoring quality of this target, the goal of this research is to minimize the maximal visiting interval. This paper firstly proposes a basic algorithm, called Basic (B-TCTP), which aims at constructing an efficient patrolling route for a number of given data mules such that the visiting intervals of all target points can be minimized. For the scenario containing weighted target points, a Weighted-TCTP (W-TCTP) algorithm is further proposed to satisfy the demand that targets with higher weights have higher data collection frequencies. By considering the energy constraint of each data mule, this paper additionally proposes a RW-TCTP algorithm which treats energy recharge station as a weighted target and arranges the data mules visiting the recharge station before exhausting their energies. Performance study demonstrates that the proposed algorithms outperform existing approaches in terms of visiting intervals of the given targets and length of patrolling path.

An energy-balanced swept-coverage mechanism for mobile WSNs

Coverage is one of the most important issues in Wireless Sensor Networks (WSNs). In literature, many coverage mechanisms have been proposed and employed mobile sensors to cover (heal) the coverage holes in the monitoring region. Consider that there are no redundant mobile sensors in a monitoring region. Some studies presented hole-movement mechanisms which used a mobile sensor to move a hole from one location to another, achieving the swept coverage of the monitoring region. However, in these studies, there are only some mobile sensors that participate in the hole-movement task, leading to an energy-unbalanced WSN. This paper considers a mobile WSN that contains holes and has no redundant mobile sensors to reach the spatial full coverage of the given monitoring region. To meet the swept coverage of the given monitoring region and balance the energies of mobile sensors, a distributed energy-balanced hole-movement mechanism, called EBHMM, is proposed. Theoretical analysis and performance evaluation reveal that the proposed EBHMM has better performance than existing hole-movement mechanisms in terms of the network lifetime and energy-balanced degree of mobile sensors.

On Distinguishing Relative Locations with Busy Tones for Wireless Sensor Networks

Bounding-box mechanism is a well known low-cost localization approach for wireless sensor networks. However, the bounding-box location information can not distinguish the relative locations of neighboring sensors, hence leading to a poor performance for some applications such as location-aware routing. This paper proposes a Distinguishing Relative Locations (DRL) mechanism which uses a mobile anchor to broadcast tones and beacons aiming at distinguishing the relative locations of any two neighboring nodes. Experimental study reveals that the proposed DRL mechanism effectively distinguishes relative locations of any two neighboring nodes and hence significantly improves the performance of location-aware routing in wireless sensor networks (WSNs).