Yu-Chieh Chen

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.

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.

Active Route-Guiding Protocols for Resisting Obstacles in Wireless Sensor Networks

In wireless sensor networks, a geographic region without the functionality of sensing and communication can generally be treated as an obstacle, which significantly impacts the performance of existing location-based routing. An obstacle can dynamically be formed due to unbalanced deployment, sensor failure, or power exhaustion, animus interference, or physical obstacles such as mountains or buildings. This paper proposes novel algorithms that enable the existing location-based routing protocols that resist obstacles. Applying the proposed active route-guiding protocol for single obstacles (S-RGP), border nodes that surround the obstacles will actively establish a forbidden region for concave obstacles and make the obstacle information transparent. Then, packets will be guided to overcome the obstacle and move along the shorter path from the encountered border node to the sink node. In addition, the proposed active route-guiding protocol for multiple obstacles (M-RGP) takes multiple obstacles into consideration and integrates their information to help the packets overcome multiple obstacles. Simulation results show that the proposed S-RGP and M-RGP create low overhead and significantly reduce the average route length, and, therefore, improve the energy consumption and end-to-end delay for a wireless sensor network with obstacles.

A novel multi-channel MAC protocol with directional antenna for enhancing spatial reuse and bandwidth utilization in WLANs

This paper aims at developing an efficient MAC protocol for wireless LAN by considering multi-channel and directional antennae. Extending IEEE 802.11 to a multi-channel environment not only exploits the bandwidth utilization but also reduces the degree of contentions. Involving directional antennae in designing multi-channel MAC protocol additionally increases the spatial reuse, allowing more parallel communications. This study proposes an efficient Multi-Channel MAC protocol with a Directional Antenna (MCDA) for WLAN. Since each station is only equipped with a single antenna, communicating pairs that progress their communications on data channels cannot maintain the channel usage information which is only obtained from the control channel, raising the channel collision problem. The proposed protocol adopts the channel switch sequence (CSS) mechanism to cope with the channel collision problem and to reduce message exchange overhead for switching channels. According to the state management, MCDA then controls directional antenna transmitting data on a selected channel to exploit the opportunities of spatial reuse, and to maintain fairness among communicating pairs. Simulation results show that the proposed MCDA protocol maintains the fairness and significantly improves bandwidth utilization and throughput.

BUFE-MAC: A Protocol With Bandwidth Utilization and Fairness Enhancements for Mesh-Backbone-Based VANETs

Vehicular ad hoc network technologies can improve traffic safety for drivers and provide comfort services for passengers. Because the hardware of a roadside unit (RSU) is costly, in most previous research, vehicles might exchange data with an RSU through multihop transmissions. However, the vehicle with a larger number of hops to the RSU has fewer opportunities and longer time to exchange its data with the RSU because the contentions and collisions increase with the number of hops. This paper proposes the bandwidth utilization and fairness enhancements medium access control (BUFE MAC) protocol, which considers a vehicular ad hoc network that accesses the Internet through fixed Internet Gateways along the road. BUFE-MAC aims at increasing bandwidth utilization, maintaining fairness, and avoiding collision. The performance study reveals that the proposed MAC protocol not only avoids the collision problem but improves the performance in terms of end-to-end throughput and fairness as well.

On-supporting energy balanced k-barrier coverage in wireless sensor networks

The k-barrier coverage problem is known as the problem of detecting the intruders by at least k sensors when the intruders moving along the crossing paths from one boundary to another. This paper proposes decentralized algorithms to cope with the k-barrier coverage problem. For a given value k, the proposed algorithms find out the maximum disjoint sets of sensors such that each set of sensors meets the requirement of k-barrier coverage for users. Three mechanisms, called Basic, Backtracking, and Branch, are proposed for constructing as more as possible the disjoint sets of sensors that satisfy the requirement of k-barrier coverage. Performance study reveals that the proposed algorithms achieve near-optimal performance.

Decentralized and energy-balanced algorithms for maintaining temporal full-coverage in mobile WSNs

Coverage is one of the most important issues in Wireless Sensor Networks (WSNs). However, full coverage only can be achieved when surplus mobile sensors contribute a coverage area larger than the hole size. When there is no surplus mobile sensor to cover a big hole, previous studies have utilized mobile sensors by moving the hole from one location to another, therefore achieving temporal full-coverage, where each location on the monitoring region has been ever covered by mobile sensors during a fixed time interval. However, with only some mobile sensors participating in the hole-movement task, this results in an energy-imbalance WSN. This paper considers a mobile WSN that contains a big hole where there exists no redundant mobile sensor to heal the hole. Three distributed algorithms, called Basic, Forward-Only, and Any-Direction movement mechanisms, are proposed to achieve the purpose of temporal full-coverage in a way that the total energy consumption is minimized or that the energy consumption of all mobile sensors that participate in the hole-movement task are balanced. Simulation results reveal that the proposed hole-movement mechanisms enhance the coverage of WSNs and balance the energy consumption of mobile sensor nodes. Copyright

A dead-end free deployment algorithm for wireless sensor networks with obstacles

In wireless sensor networks (WSNs), the performance of robot deployment is highly determined by the obstacle-resistance capability which refers to how well the robot can overcome the Dead-End problem and deploy minimal number of sensors for achieving full coverage even though the environment contains multiple obstacles. This paper presents a Dead-End free robot deployment algorithm, called DFD, that efficiently deploys minimal number of sensors for achieving full coverage while the Dead-End problem raised by obstacles can be overcome. Performance results reveal that the proposed DFD outperforms existing robot deployment mechanisms in terms of coverage ratio, energy consumption as well as deployment time.

WRGP: Weight-Aware Route Guiding Protocol for Wireless Sensor Networks with Obstacles

The greedy forwarding routing protocol has been widely used for constructing a route with low control overheads in wireless sensor networks. However, its performance drops significantly when obstacles exist. This paper proposes a novel mechanism, named WRGP, which removes the impact of obstacles on the greedy forwarding routing. The proposed WRGP initially applies the previous research to specify the border nodes that surround the obstacle. Then the border nodes in the concave region of the obstacle initiate the weight assigning process and establish a forbidden region to prevent the packets from entering the concave region. Finally WRGP specifies some border nodes to act as the effective border nodes for constructing the optimal routes from themselves to the sink node. Comparing with the existing obstacles-resisting protocols, the proposed WRGP avoids the ping-pong effect and guides the packets moving along the shortest path from the encountered effective border node to the sink node. In addition, the M-WRGP is further developed to cope with the multi-obstacle problem. Simulation results show that both WRGP and M-WRGP outperform the existing protocol PAGER in terms of control overheads and average route length.

Energy-Efficient Mechanisms for Coverage Recovery in WSNs

In wireless sensor networks (WSNs), coverage of the monitoring area represents the quality of service (QoS) related to the surveillance. In literature, a number of studies developed robot deployment and patrol algorithms. However, the efficiency of existing repair algorithms can be further improved in terms of time and energy consumption. Moreover, existing repair algorithms did not consider the existence of obstacles and the constraint of limited energy of the robot. This paper presents novel tracking mechanism and robot repairing algorithm for maintaining the coverage quality for a given WSN. Without the support of location information, the tracking mechanism leaves the robots foot marks such that sensors that are nearby the failure region 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 optimal route that passes through all failure regions with minimal overhead in terms of the required time and power consumption. In addition, the proposed repairing algorithm also considers the remaining energy of the robot so that the robot can be back to home for recharging energy and overcome the unpredicted obstacles. Performance study reveals that the developed protocol can efficiently maintain the coverage quality while the required time and energy consumption are significantly reduced.