Seong-eun Yoo

Shortcut Tree Routing in ZigBee Networks

ZigBee is the emerging industrial standard for ad hoc networks based on IEEE 802.15.4. Due to characteristics such as low data rate, low price, and low power consumption, ZigBee is expected to be used in wireless sensor networks for remote monitoring, home control, and industrial automation. Since one of the most important goals is to reduce the installation and running cost, ZigBee stack is embedded in small and cheap micro-controller units. Since tree routing does not require any routing tables to send the packet to the destination, it can be used in ZigBee end devices that have limited resources. However, tree routing has the problem that the packets follow the tree topology to the destination even if the destination is located nearby. We propose the shortcut tree routing protocol to reduce the routing cost of ZigBee tree routing by using the neighbor table that is originally defined in the ZigBee standard. While following the ZigBee tree routing algorithm, we suggest forwarding the packet to the neighbor node if it can reduce the routing cost to the destination. Simulation results show that the shortcut tree routing algorithm saves more than 30 percent of the hop count compared with ZigBee tree routing.

Guaranteeing Real-Time Services for Industrial Wireless Sensor Networks With IEEE 802.15.4

Industrial applications of wireless sensor networks require timeliness in exchanging messages among nodes. Although IEEE 802.15.4 provides a superframe structure for real-time communication, a real-time message-scheduling algorithm is still required to schedule a large number of real-time messages to meet their timing constraints. We propose a distance-constrained real-time offline message-scheduling algorithm which generates the standard specific parameters such as beacon order, superframe order, and guaranteed-time-slot information and allocates each periodic real-time message to superframe slots for a given message set. The proposed scheduling algorithm is evaluated and analyzed extensively through simulations. In addition, a guaranteed time service is implemented in a typical industrial sensor node platform with a well-known IEEE 802.15.4-compliant transceiver CC2420 and ATmega128L to verify the feasibility of the guaranteed time service with the schedule generated by the proposed scheduling algorithm. Through experiments, we prove that the real system runs accurately according to the schedule calculated by the proposed algorithm.

A 2 S: Automated Agriculture System based on WSN

This paper describes the results of real deployment of A S which consists of WSN(Wireless Sensor Network) to monitor and control the environments and a management sub-system to manage the WSN and provide various and convenient services to consumers with hand-held devices such as a PDA living a farming village. The WSN were deployed in greenhouses with melon and cabbage in Dongbu Handong Seed Research Center. A S was used to monitor the growing process of them and control the environment of the greenhouses. We acquired valuable experiences and ideas from this real deployment and operation of A S and believe that they can be useful in consumer electronics field such as home network as well as automated agriculture field. .

Neighbor Table Based Shortcut Tree Routing in ZigBee Wireless Networks

The ZigBee tree routing is widely used in many resource-limited devices and applications, since it does not require any routing table and route discovery overhead to send a packet to the destination. However, the ZigBee tree routing has the fundamental limitation that a packet follows the tree topology; thus, it cannot provide the optimal routing path. In this paper, we propose the shortcut tree routing (STR) protocol that provides the near optimal routing path as well as maintains the advantages of the ZigBee tree routing such as no route discovery overhead and low memory consumption. The main idea of the shortcut tree routing is to calculate remaining hops from an arbitrary source to the destination using the hierarchical addressing scheme in ZigBee, and each source or intermediate node forwards a packet to the neighbor node with the smallest remaining hops in its neighbor table. The shortcut tree routing is fully distributed and compatible with ZigBee standard in that it only utilizes addressing scheme and neighbor table without any changes of the specification. The mathematical analysis proves that the 1-hop neighbor information improves overall network performances by providing an efficient routing path and distributing the traffic load concentrated on the tree links. In the performance evaluation, we show that the shortcut tree routing achieves the comparable performance to AODV with limited overhead of neighbor table maintenance as well as overwhelms the ZigBee tree routing in all the network conditions such as network density, network configurations, traffic type, and the network traffic.

PGS: Parking Guidance System based on wireless sensor network

In this paper, we present PGS, a parking guidance system based on wireless sensor network(WSN) which guides a driver to an available parking lot. The system consists of a WSN-based VDS(vehicle detection sub-system) and a management sub-system. The WSN based VDS gathers information on the availability of each parking lot and the management sub-system processes the information and refines them and guides the driver to the available parking lot by controlling a VMS(Variable Messaging System). The paper describes the overall system architecture of PGS from the hardware platform to the application software in the view point of a WSN. We implemented the WSN based VDS of PGS and experimented on the system with several kinds of cars. The experimental results show that PGS succeeds in detecting various kinds of cars and the predicted battery life-time using measured current profiles is over 5 years.

Scheduling support for guaranteed time services in IEEE 802.15.4 low rate WPAN

We propose a real-time message scheduling algorithm which is applied to schedule periodic real-time messages in IEEE 802.15.4 for LR-WPAN (low rate wireless personal area network). The standard allows GTSs (guaranteed time slots) in the optional use of a superframe structure in a beacon-enabled network to be used to exchange real-time messages. To utilize these features of the standard efficiently, a proper message scheduling algorithm is needed. The proposed offline message scheduling algorithm which is based on a distance constrained scheduler generates the standard specific parameters including BO, SO, and GTS information to schedule the given message set. The algorithm is evaluated by simulation and the guaranteed time service using the schedule is implemented and evaluated on CC2420DB which is a prototyping platform including an IEEE 802.15.4 compliant transceiver of Chipcon AS.

Cluster-based hierarchical time synchronization for multi-hop wireless sensor networks

In this paper, we propose the cluster-based hierarchical time synchronization protocol (CHTS) for wireless sensor networks (WSN). To couple the network with real world tightly, we provide a network-wide time synchronization through the introduction of abstractions for cluster and hierarchy. Generally the error of time synchronization has the tendency of being accumulated as the hop count along the synchronization path increases in multi-hop wireless sensor network. Thus we cluster the randomly deployed nodes to decrease the hop count along the synchronization path. We then apply different optimal synchronization mechanisms to the cluster heads and cluster members for the sake of power efficiency through an explicit broadcast manner. We prove the performance enhancements with simulation comparisons.

DGS: Driving Guidance System Based on Wireless Sensor Network

In this paper, we present DGS, a driving guidance system based on wireless sensor networks (WSN) which guides a driver to drive a car in safety. The system consists of two sub-systems: SMS (speed measurement sub-system) and WPS (weather information providing sub-system). SMS measures the speed of a car and captures the image of the speeding car using a speed camera. WPS provides weather information including the road conditions (icy, wet, etc.) via VMS or a telematics terminal. The paper describes the overall system architecture of DGS from the hardware platform to the application software in the view point of a WSN. We implemented the WSN based SMS of DGS from hardware to application software. The experimental results show that the accuracy of speed measurement is over 99% at 80 kmph and the predicted battery life-time using measured current profiles is about 3 years. We also discuss the lessons acquired from the real-life experiments we performed. We believe that the lessons can be useful in other WSN applications as well as in typical telematics applications.

Wireless Sensor Networks for Cultural Property Protection

Wireless sensor network technology has been proven to have a strong impact on our daily life from many real applications. In this paper wireless sensor networks for cultural property protection are introduced. We deployed wireless sensor networks in Bul-guk-sa Temple, which is one of the most important UNESCO cultural property sites in Korea. This paper presents our wireless sensor network system for monitoring and protecting cultural property from the aspect of application design to network system management.

Energy efficient and seamless data collection with mobile sinks in massive sensor networks

Wireless Sensor Networks (WSNs) enable the surveillance and reconnaissance of a particular area with low cost and less manpower. However, the biggest problem against the commercialization of the WSN is the limited lifetime of the battery-operated sensor node. Taking this problem into account, a mobile sink is deployed as a robot, vehicle or portable device to only activate the sensor nodes that are interesting to the sink and leaves other nodes deactivated for. This can considerably extend the lifetime of the sensor nodes compared to existing power management algorithm of using all nodes. However, in this environment, the mobility of the sink raises new issues of energy efficiency and connectivity in communications. To solve these issues, we propose a DRMOS (Dynamic Routing protocol for Mobile Sink) method that includes a designated wake-up-zone to make sensor nodes prepare for an incoming sink. The shape of the wake-up-zone is dynamically changing to reflect the past moving patterns of the sinks. Moreover, we present the extensive simulation results and recommend parameters for practical use of DRMOS from the simulation analysis.