Meng-Shiuan Pan

Wireless sensor networks for emergency navigation

In an emergency, wireless network sensors combined with a navigation algorithm could help safely guide people to a building exit while helping them avoid hazardous areas. We propose a distributed navigation algorithm for emergency situations. At normal time, sensors monitor the environment. When the sensors detect emergency events, our protocol quickly separates hazardous areas from safe areas, and the sensors establish escape paths. Simulation and implementation results show that our scheme achieves navigation safety and quick convergence of the navigation directions. We based our protocol on the temporally ordered routing algorithm for mobile ad hoc networks. TORA assigns mobile nodes temporally ordered sequence numbers to support multipath routing from a source to a specific destination node

Emergency guiding and monitoring applications in indoor 3D environments by wireless sensor networks

Recently, Wireless Sensor Networks (WSNs) have been widely discussed in many applications. In this paper, we propose a novel Three-Dimensional (3D) emergency service that aims to guide people to safe places when emergencies happen. At normal time, the network is responsible for monitoring the environment. When emergency events are detected, the network can adaptively modify its topology to ensure transportation reliability, quickly identify hazardous regions that should be avoided and find safe navigation paths that can lead people to exits. In particular, the structures of Three-Dimensional buildings are taken into account in our design. Simulation results shows that our protocols can adapt emergencies quickly at low message cost and can find safer paths to exits than existing results

The Orphan Problem in ZigBee Wireless Networks

ZigBee is a communication standard which is considered to be suitable for wireless sensor networks. In ZigBee, a device (with a permanent 64-bit MAC address) is said to join a network if it can successfully obtain a 16-bit network address from a parent device. Parent devices calculate addresses for their child devices by a distributed address assignment scheme. This assignment is easy to implement, but it restricts the number of children of a device and the depth of the network. We observe that the ZigBee address assignment policy is too conservative, thus usually making the utilization of the address pool poor. Those devices that cannot receive network addresses will be isolated from the network and become orphan nodes. In this paper, we show that the orphan problem can be divided into two subproblems: the bounded-degree-and-depth tree formation (BDDTF) problem and the end-device maximum matching (EDMM) problem. We then propose algorithms to relieve the orphan problem. Our simulation results show that the proposed schemes can effectively reduce the number of orphan devices compared to the ZigBee strategy.

Quick convergecast in ZigBee beacon-enabled tree-based wireless sensor networks

Convergecast is a fundamental operation in wireless sensor networks. Existing convergecast solutions have focused on reducing latency and energy consumption. However, a good design should be compliant to standards, in addition to considering these factors. Based on this observation, this paper defines a minimum delay beacon scheduling problem for quick convergecast in ZigBee tree-based wireless sensor networks and proves that this problem is NP-complete. Our formulation is compliant with the low-power design of IEEE 802.15.4. We then propose optimal solutions for special cases and heuristic algorithms for general cases. Simulation results show that the proposed algorithms can indeed achieve quick convergecast.

Address Assignment and Routing Schemes for ZigBee-Based Long-Thin Wireless Sensor Networks

Wireless sensor networks (WSNs) have been extensively researched recently. This paper makes two contributions to this field. First, we promote a new concept of long-thin (LT) topology for WSNs, where a network may have a number of linear paths of nodes as backbones connecting to each other. These backbones are to extend the network to the intended coverage areas. At the first glance, a LT WSN only seems to be a special case of numerous WSN topologies. However, we observe, from real deployment experiments, that such a topology is quite general in many applications and deployments. The second contribution is that we show that the address assignment and thus the tree routing scheme defined in the original ZigBee specification may work poorly, if not fail, in a LT topology. We thus propose simple, yet efficient, address assignment and routing schemes for a LT WSN. Simulation results and prototyping experiences are also reported.

The orphan problem in zigbee-based wireless sensor networks

ZigBee is a standard which is considered to be suitable for wireless sensor networks. In ZigBee, a device is said to join a network if it can obtain a network address from a parent device. Devices calculate addresses for their child devices by a distributed address assignment scheme. This assignment is easy to implement, but it restricts the number of children of a device and the depth of the network. We observe that if one uses the random formation policy specified in ZigBee, the utilization of the address pool will be very low. Those devices that can not receive network addresses will be isolated from the network and become orphan nodes. In this paper, we model the orphan problem by two subproblems: the bounded-degree-and-depth tree formation (BDDTF) problem and the end-device maximum matching (EDMM) problem. We then present solutions to these problems. The results can be applied to network formation in ZigBee networks.

An adaptive MAC protocol for wireless ad hoc networks using smart antenna system

In the wireless ad hoc networks, the channel is normally underutilized because of using the omnidirectional antennas. In this paper, we designed an adaptive MAC protocol using the smart antenna systems to improve the channel utilization of the wireless ad hoc networks. Nodes utilize the position information gathered by GPS to steer their main lobes to the desired directions, and perform the power control to further increase the channel utilization. Moreover, the neighbors adaptively adjust their antenna beam patterns to avoid interfering with the communicating nodes. The simulation results show that the network throughput can be efficiently improved when applying our adaptive MAC protocol using smart antenna system.

Quick convergecast in ZigBee/IEEE 802.15.4 tree-based wireless sensor networks

Convergecast is a fundamental operation in wireless sensor networks. Existing convergecast solutions have focused on reducing latency and energy consumption. However, a good design should be compliant to standards, in addition to considering these factors. Based on this observation, this paper defines a minimum delay beacon scheduling problem for quick convergecast in ZigBee/IEEE 802.15.4 tree-based wireless sensor networks and proves that this problem is NP-complete. Our formulation is also compliant with the low-power design of IEEE 802.15.4. We then propose optimal solutions for special cases and heuristic algorithms for general cases. Simulation results show that the proposed algorithms can indeed achieve quick convergecast.

Two-Way Beacon Scheduling in ZigBee Tree-Based Wireless Sensor Networks

Broadcast and convergecast are two fundamental operations in wireless sensor networks. Although previous works have addressed energy-efficient and low-latency scheduling, these works either consider only one-way (broadcast or convergecast) communication or are not compliant to Zig-Bee/IEEE 802.15.4 standards. Motivated by these observations, this work defines a two-way beacon scheduling problem for ZigBee tree-based networks. We propose a scheduling algorithm that can reduce indirect interference neighbors and achieve low-latency broadcast and convergecast. Simulation results are presented.

A lightweight network repair scheme for data collection applications in zigbee WSNs

Data collection is a fundamental operation in wireless sensor networks (WSNs). In, a quick convergecast solution is proposed for data collection in a ZigBee beacon-enabled tree-based WSN. However, it does not consider the network repair issue. When a ZigBee router loses its link to its parent, all its descendants have to rejoin the network. The rejoining procedure is time-consuming and may incur high communication overheads. The proposed network repair scheme consists of a regular repair and an instant repair schemes. Periodically, the network coordinator can issue regular repair to refresh the network (so as to keep the network in good shape). During normal operations, if a router loses its parent, it tries instant repair to reconnect to a new parent. Our design thus improves over ZigBee in that nodes can continue their operations even during instant repair.