Antoine Gallais

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.

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.

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.

Performance evaluation and enhancement of surface coverage relay protocol

Area coverage protocols aim at turning off redundant sensor nodes while ensuring full coverage of the area by the remaining active nodes. 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 and very few are robust to non ideal physical conditions. In this paper, we propose a deep analysis and some enhancements of a localized algorithm for area coverage, based on Surface Coverage Relays (SCR) and able to build connected active nodes sets that fully cover the area. We first enhanced the critical phase of our protocol (the relay selection) and show that the number of active nodes can be drastically reduced. We then raise the issue of the robustness of the protocol once a realistic physical layer is simulated. Our algorithm proved itself to be an interesting solution as it remained able to still ensure high coverage level under realistic physical layer conditions. We also added the possibility to finely tune the overall proportion of active nodes through a new parameter used during local relay selection phases.