Yongbin Yim

A Cluster-Based Continuous Object Tracking Scheme in Wireless Sensor Networks

Due to the severe resource constraints of sensor hardware, energy efficiency is a principal factor for detecting and tracking the movement of the large-scale phenomena such as wild fire, poison gas and hazardous bio-chemical material, denoted by continuous objects. In order to save the energy, the selective wakeup approach is effective way in the wireless sensor networks. However, most previous researches concentrated on individual objects such as intruders, tanks, and animals cannot be applied to the continuous object tracking because it is hard to expect that the diffusion of continuous object has the uniform velocity or acceleration. Recently, a prediction-based selective wakeup algorithm, denoted by PRECO is proposed. Nevertheless, this mechanism is still not acceptable. First, its prediction result is very inaccurate because a sensor node calculates next boundary line with only a few data while the continuous objects are pretty flexible and vicissitudinous. Second, its prediction tasks among current boundary nodes should be operated at the same time but it is a hard problem for the nodes to have synchronization in the wireless sensor networks. Therefore, we propose a novel prediction and selective wakeup scheme for energy efficient and accuracy continuous object tracking by using structured clustering. Hence, when objects are detected in some specific area, appointed areas where the target may move activate to keep guard without any complex calculations. Moreover, our scheme is asynchronous so that it is suitable for the sensor networks.

Quality-based event reliability protocol in wireless sensor networks

For reliable event detection in wireless sensor networks, a sink requires collective information reported by sensor nodes sensing an event. In other words, the sink has to receive a certain amount of data dealing with the event for reliable event detection. Existing studies propose quantity-based event reliability protocols that improve event reliability by increasing the number of data successfully transmitted by controlling transport process. These studies present diverse schemes to successfully transmit as many reporting data as possible such as diversification of routing path for congestion avoidance and control of data reporting frequency rate for transport error compensation. However, since it frequently happens that wireless sensor networks with restricted capacity cannot deliver more than required amount of data due to data collision and congestion, the quantity-based event reliability protocols have limitation to raise the possibility of event detection. In this paper, we proposes a Quality-based Event Reliability Protocol (QERP) utilizing a property that the reporting data from sensor nodes are different in the contribution degree (CD) for event detection according to their environmental conditions. QERP selects sensor nodes to send their reporting data according to CD, and differentially transports them by CD-based buffer management and load balancing. Simulation results show that QERP detect more reliably and energy-efficiently an event than quantity-based event reliability protocols.

A Radio-disjoint Geographic Multipath Routing in Wireless Sensor Networks

Geographic multipath routing is one of the most appropriate approaches which can improve the end-to-end reliability via multiple paths for the wireless sensor networks that have frequent network dynamics such as both node and link failures. It has been focused on how to construct a node-disjoint multipath that an intermediate node should be belonged by only a single path. It is because that if two or more paths share one intermediate node, the node may be congested by multiple traffics. Even it might bring multiple path failures if the shared node fails. However, if the node-disjoint multipath schemes are used, there might be another significant problem such as transmission failure or corrupted packet reception due to collisions between adjacent paths. Therefore, we propose a radio-disjoint geographic multipath scheme to avoid the collisions, which allow multiple paths to keep a certain distance between each other. Unfortunately, this simple idea still remains inevitable interference regions, i.e., both source side and destination side. So we eliminate the interferences in these regions by using local scheduling algorithms. We demonstrate that the proposed protocol shows better performance than the previous studies via extensive simulation in terms of end-to-end packet delivery ratio and the end-to-end delay.

Non-Geographical Shortest Path Data Dissemination for Mobile Sinks in Wireless Sensor Networks

In wireless sensor networks (WSNs), the studies that support sink mobility without location information of sensor nodes traditionally establish a cluster-based virtual infrastructure. The cluster-based infrastructure consists of clusters involving sensor nodes and a shared tree organized by the cluster heads. In the studies, data dissemination from a source node to a mobile sink is performed via the shared tree. The mobile sink makes connection from the current standing cluster into the root of the shared tree; the source transmits data to the root; and the root delivers the data to the mobile sink. Namely, the data from a source may always be detoured to a mobile sink via the shared tree. According to a change of the current standing cluster, the mobile sink could frequently remake connection into the root; thus, excessive energy consumption by the detour problem might seriously happen. In this paper, we propose a communication protocol that provides the shortest path from a source to a sink by exchanging a routing table between neighboring cluster heads. The routing table contains the cluster ID of a neighbor cluster and hop-count from the neighbor cluster to the other clusters. A sink registers the cluster ID of the current standing cluster into the root of the shared tree, and a source then obtains the cluster ID. Thus, the source can deliver data directly to the current standing cluster of the mobile sink. Simulation results show that the proposed protocol is superior to the existing protocol.

An opportunistic routing for real-time data in Wireless Sensor Networks

In this paper, we propose an opportunistic real-time data dissemination protocol in order to solve the transmission failure problem in error-prone WSNs. Retransmission is wellknown for recovery of transmission failure, however, this may cause the severe time delay possibly to violate the real-time requirement. To solve the problem, our protocol exploits both broadcasting nature and temporal opportunity concept. In a radio-range of a sensor node, there may be multiple neighbor nodes to satisfy the real-time requirement. By broadcasting property, all neighbors can receive a data from a node, and only each satisfying neighbor decides its relay toward the destination by using temporal selection function. The temporal function is related to the tolerable time period to be able to satisfy the realtime requirement. By giving the priority to the node with smaller tolerable time, we have more opportunities to forward toward the destination. That is, even if a node with a long tolerable time waits for the longer period of time, it still has a chance to forward with the real-time requirement. In summary, the proposed protocol attains the high reliability and real-time requirement by removing data retransmission and multiple opportunities with temporal consideration. Simulation results show that the proposed protocol is superior to the existing real-time protocols in terms of real-time data dissemination and energy consumption.

Distributed Forwarder Selection for Beaconless Real-Time Routing in Wireless Sensor Networks

In wireless sensor networks (WSNs), real-time service is one of the important issues. Typically, existing studies for the service are relied on beacons. Recently, beaconless routing has been proposed to overcome control overhead for resource constrained environment of WSNs. Thus, real-time communication based on the beaconless scheme could give great advantages with less energy consumption. To do that, however, it brings new challenges. For the real-time communication, each node needs to be aware of single hop delay for data forwarding within desired time. In conventional approaches, it is based on delay in neighbor information through beacons. An appropriate next forwarder is selected by a sender. However, in the beaconless scheme, a sender could not select a next forwarder since that is determined by a receiver after transmitting data. Also, contention delay is included in single hop delay for beaconless routing. Thus, the delay estimation principle should be renovated. In this paper, we present a receiver-based beaconless routing for real-time services. We design a novel delay estimation strategy. The single hop delay from a sender to a receiver could be calculated by a receiver but not a sender. Therefore, the receiver itself makes a decision whether desired time requirement is satisfied. Simulation experiments show that the strategy achieves higher performance in terms of energy consumption.

Distributed multicast protocol based on beaconless routing for wireless sensor networks

Distributed geographic multicast protocols are efficient and scalable for wireless sensor networks but could not be applied to beaconless routing. We propose a novel distributed multicast protocol based on beaconless routing without exchanging beacon messages.

X-geocasting: Data dissemination to mobile sink groups in wireless sensor networks

Recently, group mobility support of mobile sinks has received increasing interest, and several mechanisms have been proposed. The mechanisms typically follow a strategy that simply adopts flooding. The strategy detects the currently located region of a mobile sink group in flooding, registers the current region to a source, and performs data flooding in the region to disseminate data to the sink group. However, this strategy might cause serious problems in terms of reachability and communication overhead. In the first, although a group could continuously move toward a target point for its own mission, the strategy discretely performs detecting the group region and updating the region information. Namely, data may be delivered the previously current region, i.e. already updated but changed the region. Moreover, in order to obtain the region information of the group, flooding is frequently fulfilled as well as the strategy utilizes flooding for data delivery to the group every time. Therefore, we propose a novel strategy for reachability and low overhead, called X-Geocasting. X-Geocasting merely finds out the region of a group when the group changes direction or movement velocity. Also, instead of fully flooding in group regions, X-Geocasting predictively and flexibly determines the restricted flooding area according to direction and movement velocity. Simulation results prove this proposed group mobility support strategy provides reachability and high energy-efficiency.

Vehicle location service scheme based on road map in Vehicular Sensor Networks

Abstract Vehicular Sensor Networks (VSNs) are merging for supporting communications between roadside sensor nodes and vehicles on for notifying environment events on roads to drivers and passengers. Geographic routing has been considered as an efficient and scalable approach to send sensing data from sensor nodes to vehicles. Fundamentally, geographic routing requires sensor nodes to be aware of the location information of vehicles. Since sensor nodes are deployed around roads and vehicles move on the roads, this field property of VSNs brings about a challenging issue to provide location service of vehicles. In this paper, we propose a quorum-based location service scheme to provide sensor nodes with the location information of vehicles in VSNs. For providing the location service, the proposed scheme exploits a crossing point between a quadrangular path quorum of a location update and a line path quorum of a location query by using the road map information. Then, the proposed scheme is extended to accommodate several considerations such as voids, multiple vehicles and sources, and energy depletion. The effectiveness of the proposed scheme is analyzed and validated by extensive numerical and simulation results.

Localized disjoint multipath routing protocol in irregular wireless sensor networks

Disjoint multipath routing is an attractive approach for improving the reliability of data delivery in wireless sensor networks. Recently, the issue for maintaining the robustness and efficiency of the disjoint multipath routing against network failures such as network holes are being studied. Several protocols have been proposed to handle the network failures. However, they cause the large performance degradation on data delivery ratio and delay due to its centralized manner for detouring the network holes in irregular network environments. Thus, we propose a Localized Disjoint Multipath Routing protocol called LDMR which can achieve reliable data delivery ratio and stable data delivery delay while handling network failures. LDMR constructs the fully disjoint multipath and manages them by using a localized management method with a path priority rule. Simulation results show that our protocol provides the more stable and reliable performance than the previous protocols in terms of packet delivery ratio and packet delivery delay.