Sheng-Wen Chang

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.

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.

Novel route maintenance protocols for the Bluetooth ad hoc network with mobility

Bluetooth technology is specially designed for the wireless personal area networks to replace cable. Several challenges exist in Bluetooth scatternet formation and routing, since nodes can arrive and depart at arbitrary times. In this paper, novel route maintenance algorithms are proposed for the Bluetooth ad hoc networks, where nodes can enter or exit from the piconets time to time. Our protocols guarantee the connectivity among nodes and reconstruct the routes dynamically by considering location information of the nodes. Besides, it is proposed how to reduce the number of hops and to form the shortest route between the source and the destination due to addition of new nodes to a piconet. Performance analysis of our protocols show that they outperform in terms of end to end transmission delay, bandwidth consumption and average hop counts as compared to similar Bluetooth routing protocols that we have considered.

Location Aware Route Maintenance Protocols for the Mobile Bluetooth Radio Networks

The IEEE 802.3 energy efficient Ethernet (EEE) study group is considering rapid PHY Selection (RPS) as a mechanism to quickly switch the data rate of an Ethernet link to match link data rate with link utilization. When switching the data rate, RPS causes a momentary disruption of the link. This disruption may cause packet loss due to buffer overflow in upstream switches. We emulate RPS using PAUSE flow control and experimentally study the possible effects of RPS on TCP and UDP file transfer. We show that RPS has little or no perceivable effect on performance, but has some subtle effects on TCP throughput if PAUSE flow control is enabled in the file server.Bluetooth is a low-cost, low-power and short range communication technology, which operates in 2.4 GHz ISM band. The important research issues in Bluetooth are scatternet formation and routing, since nodes can arrive and depart at arbitrary time. In this paper, novel route maintenance algorithms are proposed for the Bluetooth scatternet that supports mobility of the nodes. Our protocols guarantee the connectivity among nodes and reconstruct the routes dynamically by taking their location information. Besides, we propose how to reduce the number of hops and to form the shortest route between the source and the destination due to addition of nodes. Performance analysis of our work shows that it outperforms in terms of end to end transmission delay, bandwidth consumption and route maintenance as compared to similar Bluetooth routing protocols.

TMCP: Two-layer multicast communication protocol for Bluetooth radio networks

Bluetooth is a low power, low cost, and short-range wireless technology developed for Personal Area Networks (PANs). A Bluetooth multicast group is a set of Bluetooth devices that desire for periodically receiving the multicast messages from the same source. For reducing the propagation delay and saving the bandwidth and energy consumptions, a multicast tree which connects all multicast members serves for the delivery of multicast messages. However, a given connected scatternet topology may not be appropriate for constructing an efficient multicast tree and hence causes power consumption and end-to-end delay. This paper develops a two-layer multicast communication protocol (TMCP) using role switching techniques for constructing an efficient multicast tree. The proposed TMCP collects as many as possible the members into the same piconet, reduces the length of multicast paths and assigns each member with a proper role. The constructed multicast tree has several features including as few as possible the non-member devices, the smallest tree level and the minimal propagation delay. Experiment results show that the TMCP offers efficient multicast service with low power consumption and small delay.

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 data-centric mechanism for Wireless Sensor Networks with weighted queries

Wireless Sensor Networks (WSNs) are characterized by their low bandwidth, limited energy, and largely distributed deployment. To reduce the flooding overhead raised by transmitting query and data information, several data-centric storage mechanisms are proposed. However, the locations of these data-centric nodes significantly impact the power consumption and efficiency for information queries and storage capabilities, especially in a multi-sink environment. This paper proposes a novel dissemination approach, which is namely the Dynamic Data-Centric Routing and Storage Mechanism (DDCRS), to dynamically determine locations of data-centric nodes according to sink nodes location and data collecting rate and automatically construct shared paths from data-centric node to multiple sinks. To save the power consumption, the data-centric node is changed when new sink nodes participate when the WSNs or some queries change their frequencies. The simulation results reveal that the proposed protocol outperforms existing protocols in terms of power conservation and power balancing.

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.

A Location Aware Mobility based Routing Protocol for the Bluetooth Scatternet

Bluetooth is a most promising technology designed for the wireless personal area networks for the cable replacement. In this paper, a location aware mobility based routing scheme for the Bluetooth scatternet is proposed that constructs the links dynamically. Our proposed routing protocol requires location information of the nodes and constructs the route between any source and destination and reduces the number of hops. Besides, the network routing problems are analyzed and role switch operations are proposed to mitigate the problems. Moreover, the roles switch and route optimization operations are also proposed to improve route performance. Rigorous simulation works are done to evaluate the performance of our protocol in terms of mobility speed and number of mobile nodes and to compare our results with similar Bluetooth routing protocols. It is observed that our protocol outperforms in terms of energy consumption and transmission packet overheads as compared to similar Bluetooth routing protocols.

A location-and-mobility aware routing protocol for Bluetooth radio networks

Bluetooth is a most promising technology designed for the wireless personal area networks for the cable replacement. In this paper, a location aware mobility based routing scheme for the Bluetooth scatternet is proposed that constructs the links dynamically. Our proposed routing protocol requires location information of the nodes and constructs the route between any source and destination and reduces the number of hops. Besides, the network routing problems are analyzed and role switch operations are proposed to mitigate the problems. Moreover, the roles switch and route optimization operations are also proposed to improve route performance. Rigorous simulation works are done to evaluate the performance of our protocol in terms of mobility speed and number of mobile nodes and to compare our results with similar Bluetooth routing protocols. It is observed that our protocol outperforms in terms of energy consumption and transmission packet overheads as compared to similar Bluetooth routing protocols.