Jean Carle

Energy-efficient area monitoring for sensor networks

The nodes in sensor networks must self-organize to monitor the target area as long as possible. Researchers at the Fundamental Computer Science Laboratory of Lille are developing strategies for selecting and updating an energy-efficient connected active sensor set that extends the network lifetime. We report on their work to optimize energy consumption in three separate problems: area coverage, request spreading, and data aggregation.

Localized Sensor Area Coverage with Low Communication Overhead

We propose several localized sensor area coverage protocols for heterogeneous sensors, each with arbitrary sensing and transmission radii. The approach has a very small communication overhead since prior knowledge about neighbor existence is not required. Each node selects a random time out and listens to messages sent by other nodes before the time out expires. Sensor nodes whose sensing area is not fully covered (or fully covered but with a disconnected set of active sensors) when the deadline expires decide to remain active for the considered round and transmit an activity message announcing it. There are four variants in our approach, depending on whether or not withdrawal and retreat messages are transmitted. Covered nodes decide to sleep, with or without transmitting a withdrawal message to inform neighbors about the status. After hearing from more neighbors, active sensors may observe that they became covered and may decide to alter their original decision and transmit a retreat message. Our simulations show a largely reduced message overhead while preserving coverage quality for the ideal MAC/physical layer. Compared to an existing method (based on hello messages followed by retreat ones and where excessive message loss contributed to excessive coverage holes), our approach has shown robustness in a model with collisions and/or a realistic physical layer.

Localized sensor area coverage with low communication overhead

We propose several localized sensor area coverage protocols for heterogeneous sensors, each with arbitrary sensing and transmission radii. The approach has a very small communication overhead since prior knowledge about neighbor existence is not required. Each node selects a random time out and listens to messages sent by other nodes before the time out expires. Sensor nodes whose sensing area is not fully covered (or fully covered but with a disconnected set of active sensors) when the deadline expires decide to remain active for the considered round and transmit an activity message announcing it. There are four variants in our approach, depending on whether or not withdrawal and retreat messages are transmitted. Covered nodes decide to sleep, with or without transmitting a withdrawal message to inform neighbors about the status. After hearing from more neighbors, active sensors may observe that they became covered and may decide to alter their original decision and transmit a retreat message. Our simulations show a largely reduced message overhead while preserving coverage quality for the ideal MAC/physical layer. Compared to an existing method (based on hello messages followed by retreat ones and where excessive message loss contributed to excessive coverage holes), our approach has shown robustness in a model with collisions and/or a realistic physical layer.

ALL-TO-ALL BROADCASTING ALGORITHMS ON HONEYCOMB NETWORKS AND APPLICATIONS

This paper presents two simple all-to-all broadcasting algorithms on honeycomb mesh. Consider a network with n processors, one has personalized routing strategy at each node and it requires a 3n communication time complexity. This communication time can be reduced to n because the computation time is always assumed to be much lower than the communication time. The other is based on a Hamiltonian path and has a 2n communication time complexity. We show how they can be used to get parallel solutions to a class of problems on honeycomb networks, among others Prefix Sums, Maximal Vectors, Maximal Sum Subsegment, Parenthesis Matching, Decoding Binary Tree, and Sorting. In our knowledge, these all-to-all broadcast algorithms are the only ones so far exhibited on a honeycomb.

Area-based beaconless reliable broadcasting in sensor networks

We consider the broadcasting problem in sensor networks where the nodes have no prior knowledge of their neighbourhood. We describe several Area-based Beaconless Broadcasting Algorithms (ABBAs). In 2D, on receiving the packet (together with geographic coordinates of the sender), each node calculates the ratio P of its perimeter, along the circle of transmission radius, that is not covered by this and previous transmissions of the same packet. The node then sets or updates its timeout to be inversely proportional to P. If the perimeter becomes fully covered, the node cancels retransmissions. Otherwise, it retransmits at the end of the timeout interval. The protocol is reliable, that is, all nodes, connected to the source, are guaranteed to receive the packet, assuming an ideal MAC layer. We also describe three 3D-ABBAs, one of them being reliable. These three protocols are based on covering three projections, covering particular points on intersection circles and covering intersection points of three spheres. Our protocols are the first reliable broadcasting protocols, other than blind flooding.

A basis for 3-D cellular networks

We propose to extend the standard concept of planar cellular networks into space. Indeed, in cellular networks the trend is to have a smaller cells to meet the growing number of communication services. The smaller the cells, the more important is the third dimension because this model is more efficient. So, it is better to take the height into account. For instance, to create a cellular network in a building, it makes no sense to have a planar cellular network. It would be better to have antennas placed in the three dimensions. This paper presents some explanations about the reason why hexagons tessellation are used in the theory of cellular networks. It describes the 3-D cellular networks used for this work and also discusses the frequency reuse mechanism and channel allocation schemes.

Ensuring Area k-Coverage in Wireless Sensor Networks with Realistic Physical Layers

Wireless sensor networks are composed of hundreds of small and low power devices deployed over a field to monitor. Energy consumption is balanced by taking advantage of the redundancy induced by the random deployment of nodes. Some nodes are active while others are in sleep mode. Area coverage protocols aim at turning off redundant sensor nodes while preserving satisfactory monitoring by the set of active nodes. The problem addressed here consists in building k distinct subsets of active nodes (layers), in a fully decentralized manner, so that each layer covers the area. In our protocol, each node selects a waiting timeout, listening to messages from neighbors. Activity messages include the layer at which a node has decided to be active. Depending on the physical layer used for sensing modeling, any node can evaluate if the provided coverage is sufficient for each layer. If so, node can sleep, otherwise it selects a layer to be active. Here, we describe a localized area coverage protocol able to maintain an area k-covered under realistic physical layer assumptions for both sensing and communicating modules.

Preserving Area Coverage in Sensor Networks with a Realistic Physical Layer

We consider the problem of activity scheduling and area coverage in sensor networks, and especially focus on problems that arise when using a more realistic physical layer. Indeed, most of the previous work in this area has been studied within an ideal environment, where messages are always correctly received. In this paper, we argue that protocols developed with such an assumption can hardly provide satisfying results in a more realistic world. To show this, we replace the classic unit disk graph model by the lognormal shadowing one. The results show that either the resulting area coverage is not sufficient or the percentage of active nodes is very high. We thus present an original method, where a node decides to turn off when there exists in its vicinity a sufficiently reliable covering set of neighbors. We show that our solution is very efficient as it preserves area coverage while minimizing the quantity of active nodes.

HIGHER DIMENSIONAL HONEYCOMB NETWORKS

We define the higher dimensional honeycomb graphs as a generalization of hexagonal plane tessellation, and consider it as a multiprocessor interconnection network. A 3-D honeycomb mesh network with n nodes has degree 4 and diameter approximately 3.63n. The network cost, defined as the product of degree and diameter, is about 20 percents better for the 3-D honeycomb than for the 3-D mesh. We describe the addressing scheme, the routing and broadcasting algorithms for three-dimensional and higher dimensional honeycombs. Furthermore, a formula for the diameter of a higher dimensional honeycomb network of given size is determined.

An Adaptive Localized Algorithm for Multiple Sensor Area Coverage

Wireless sensor networks are made up of hundreds of devices deployed over a distant or sensitive field to be monitored. Energy consumption is balanced by taking advantage of the redundancy induced by the random deployment of nodes. Some nodes are active while others are in sleep mode, thus using less energy. Such a dynamic topology should not impact the monitoring activity. Area coverage protocols aim at turning off redundant sensor nodes while ensuring full coverage of the area by the remaining active nodes. Providing k-area coverage therefore means that every physical point of the monitored field is sensed by at least fc sensor devices. Connectivity of the active nodes subset must also be provided so that monitoring reports can reach the sink stations. Existing solutions hardly address these two issues as a unified one. In this paper, we propose a localized algorithm for multiple sensor area coverage able to build connected active nodes sets. We also show that a simple feature of the protocol, called the coverage evaluation scheme, can be enhanced to handle various k-area coverage problem definitions. Experimental results show that our coverage scheme is resistant to collisions of messages as k-area-coverage of the deployment area and connectivity of the active nodes set can still be ensured.