Jeongcheol Lee

Novel service protocol for supporting remote and mobile users in wireless sensor networks with multiple static sinks

A wireless sensor network typically consists of users, a sink, and a number of sensor nodes. The users may be remotely connected to a wireless sensor network and via legacy networks such as Internet or Satellite the remote users obtain data collected by the sink that is statically located at a border of the wireless sensor network. However, in practical sensor network applications, there might be two types of users: the traditional remote users and mobile users such as firefighters and soldiers. The mobile users may move around sensor fields and they communicate with the static sink only via the wireless sensor networks in order to obtain data like location information of victims in disaster areas. For supporting the mobile users, existing studies consider temporary structures. However, the temporary structures are constructed per each mobile user or each source nodes so that it causes large energy consumption of sensor nodes. Moreover, since some of them establish the source-based structure, sinks in them cannot gather collective information like mean temperature and object detection. In this paper, to effectively support both the remote users and the mobile users, we propose a novel service protocol relying on the typical wireless sensor network. In the protocol, multiple static sinks connect with legacy networks and divide a sensor field into the number of the multiple sinks. Through sharing queries and data via the legacy networks, the multiple static sinks provide high throughput through distributed data gathering and low latency through short-hops data delivery. Multiple static sinks deliver the aggregated data to the remote users via the legacy networks. In case of the mobile users, when a mobile user moves around, it receives the aggregated data from the nearest static sink. Simulation results show that the proposed protocol is more efficient in terms of energy consumption, data delivery ratio, and delay than the existing protocols.

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.

Circle Path Based Sink Location Service for Geographic Routing Scheme

Geographic routing has been considered as an efficient, simple, and scalable routing protocol for wireless sensor networks since it exploits pure local location information instead of global topology information to route data packets. Geographic routing requires the sources nodes to be aware of the location of sinks. Most existing geographic routing protocols merely assume that source nodes are aware of the locations of sinks or can get the locations of sinks by some service. How can source nodes get the locations of sinks was not addressed in detail. In this paper, we propose a Circle Path Based Sink Location Service for Geographic Routing in wireless sensor networks. In this scheme, a source node sends a Sink Location Query (SLQ) message to the predefined Base Node and sends another SLQ message to a node on the edge of the sensor network, thus generating a SLQ path; a sink node sends a Sink Location Announcement (SLA) message along a circle path, the centre of the circle path is the predefined Base Node. By this way we can guarantee the SLQ path and SLA path have at least one crossing point. The node located on the crossing point of the two paths informs the source node the sink location. How to achieve this procedure in any irregular profile sensor network is another challenge of this paper. Simulation results show that our protocol is significantly superior to other protocols in terms of energy consumption and control overhead.

Multicast Protocol for Real-Time Data Dissemination in Wireless Sensor Networks

Real-time data dissemination to a multicast group is data delivery to each member in the multicast group within the desired time deadline. The hardest aspect of this mission is to enforce the real-time constraint in the communication between a source and the furthest member since an end-to-end delay is proportional to a physical distance in wireless sensor networks. We call it the critical distance. The critical distance should be most important constraint for real-time multicasting. That is, the delivery distance from a source to each member should not be longer than the critical distance even by any reason. However, since the traditional multicast protocols lay the strong emphasis only on the overall communication cost rather than delivery distance to each member, they may violate the real-time constraint related to the critical distance. In this letter, we propose a novel multicast protocol for real-time data dissemination.

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.

Region Based Data Dissemination Scheme for Mobile Sink Groups in Wireless Sensor Networks

In many applications of Wireless Sensor Networks (WSNs), the sensing data are disseminated from a source to multiple mobile sinks. Since WSNs consists of a number of sensor nodes with limited capabilities, previous studies mainly discuss on how to send the data efficiently and do not consider the group mobility of mobile sinks that move together staying closely and randomly move within a geographically restricted region. Although the existing multicasting protocols could be applied, they suffer from high congestion and control overhead due to location updates by individual mobile sinks. Geocasting protocols are effective for data delivery to a sink group within a restricted region, but do not guarantee since they only focus on transmitting data to all nodes within a stationary region. Therefore, we propose Region Based Data Dissemination (RBDD) scheme to address these problems. RBDD provides efficient data dissemination scheme for mobile sink groups, so it guarantees data transmission when a sink group does not only move as a whole, but its member sinks also move inside of the region or outside of it. Simulation results show that RBDD guarantees data delivery to a mobile sink group.

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.

Sink Location Service via Inner Rectangular in Wireless Sensor Networks

Geographic routing has been considered as an efficient, simple, and scalable routing protocol for wireless sensor networks since it exploits pure location information instead of global topology information to route data packets. Geographic routing requires the source nodes to be aware of the location of the sink nodes. How source nodes efficiently obtain the sink location information has been merely studied yet. In this paper, we propose a Sink Location Service via Inner Rectangular in Wireless Sensor Networks. A source node and a sink node send location queries and location announcement messages to specified direction respectively by geographic routing; thus, a sink location query path and a sink location announcement path is generated. The node located on a crossing point of these two paths informs the source node about the sink location information. Then the source node sends data to the sink node by geographic routing. The proposed scheme constructs a virtual restricted linear flooding zone inside the network to guarantee the existence of the crossing point. Simulation results show that proposed scheme is reliable and efficient than the existing protocols.

A Chaining Selective Wakeup Strategy for a Robust Continuous Object Tracking in Practical Wireless Sensor Networks

The selective wakeup scheme is the energy saving mechanism that is used for an object detecting or tracking in wireless sensor networks. Recently, many protocols are proposed using the selective wakeup scheme for the continuous objects tracking such as forest fires, poison gas, and oil spills. They predict the future shape of the continuous objects and activate only sensors in the predicted boundary area of the objects. It works normally in a uniformly deployed wireless sensor networks. However, it cannot be directly applied to a randomly deployed practical sensor networks with void areas. When a void area is around the boundary area, the activation message cannot reach to the next activation area and the activation control will be fail. Moreover, if activation control is once foiled then the next activation control might be failed continuously. It leads to many detection errors for continuous object. The detection errors can be result in serious harm to people, because most of continuous objects are dangerous substances. In this paper, we propose a chaining selective wakeup scheme for robust continuous object tracking in wireless sensor networks. In our protocol, we collect the information of a void area during the network configuration time, if the next boundary area is in the void area, we activate the chained area surrounding the void area with activation control message. Simulation results show the better performance than the previous studies in terms of success ratio of continuous objects detection and tracking.

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.