1,906 research outputs found

    A Feasibility Check for Geographical Cluster Based Routing under Inaccurate Node Localization in Wireless Sensor Networks

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    Localized geographic single path routing along a wireless network graph requires exact location information about the network nodes to assure message delivery guarantees. Node localization in practice however is not exact. Errors ranging from several centimeters up to several meters are usual. How to perform localized routing in practice when such errors are prevalent? In this work we look at a promising routing variant which does not completely overcome this practical problem but which mitigates it. The concept does away with trying to find node positions as precise as possible but allows inaccuracies from the very beginning. It partitions the plane by a regular mesh of hexagons. The only information which is of interest is in which cell of that partitioning a node is located in. Using this node embedding, a virtual geographic overlay graph can then be constructed. To find the node positions we apply three variants of multidimensional scaling, two of them being a node localization approach which has been well studied in the context of sensor networks and one which we apply here for the first time in that context. Using the location information we get from these localization approaches we embed the nodes into the clusters their location falls into. We define two graph metrics to assess the quality of the overlay graph obtained by the embedding. Applying these two metrics in a simulation study, we show that cluster based routing is an eligible approach to support localized geographic routing when location errors are prevalent

    Evolutionary Construction of Geographical Networks with Nearly Optimal Robustness and Efficient Routing Properties

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    Robust and efficient design of networks on a realistic geographical space is one of the important issues for the realization of dependable communication systems. In this paper, based on a percolation theory and a geometric graph property, we investigate such a design from the following viewpoints: 1) network evolution according to a spatially heterogeneous population, 2) trimodal low degrees for the tolerant connectivity against both failures and attacks, and 3) decentralized routing within short paths. Furthermore, we point out the weakened tolerance by geographical constraints on local cycles, and propose a practical strategy by adding a small fraction of shortcut links between randomly chosen nodes in order to improve the robustness to a similar level to that of the optimal bimodal networks with a larger degree O(N)O(\sqrt{N}) for the network size NN. These properties will be useful for constructing future ad-hoc networks in wide-area communications.Comment: 14 pages, 10 figures, 1 tabl

    Energy efficient geographic routing for wireless sensor networks.

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    A wireless sensor network consists of a large number of low-power nodes equipped with wireless radio. For two nodes not in mutual transmission range, message exchanges need to be relayed through a series of intermediate nodes, which is a process known as multi-hop routing. The design of efficient routing protocols for dynamic network topologies is a crucial for scalable sensor networks. Geographic routing is a recently developed technique that uses locally available position information of nodes to make packet forwarding decisions. This dissertation develops a framework for energy efficient geographic routing. This framework includes a path pruning strategy by exploiting the channel listening capability, an anchor-based routing protocol using anchors to act as relay nodes between source and destination, a geographic multicast algorithm clustering destinations that can share the same next hop, and a lifetime-aware routing algorithm to prolong the lifetime of wireless sensor networks by considering four important factors: PRR (Packet Reception Rate), forwarding history, progress and remaining energy. This dissertation discusses the system design, theoretic analysis, simulation and testbed implementation involved in the aforementioned framework. It is shown that the proposed design significantly improves the routing efficiency in sensor networks over existing geographic routing protocols. The routing methods developed in this dissertation are also applicable to other location-based wireless networks

    A clustered back-bone for routing in ad-hoc networks

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    In the recent years, a lot of research work has been undertaken in the area of ad-hoc networks due to the increasing potential of putting them to commercial use in various types of mobile computing devices. Topology control in ad-hoc networks is a widely researched topic; with a number of algorithms being proposed for the construction of a power-efficient topology that optimizes the battery usage of the mobile nodes. This research proposes a novel technique of partitioning the ad-hoc network into virtually-disjoint clusters. The ultimate aim of forming a routing graph over which power-efficient routing can be implemented in a simple and effective manner is realized by partitioning the network into disjoint clusters and thereafter joining them through gateways to form a connected, planar back-bone which is also a t-spanner of the original Unit Disk Graph (UDG). Some of the previously proposed algorithms require the nodes to construct local variations of the Delaunay Triangulation and undertake several complicated steps for ensuring the planarity of the back-bone graph. The construction of the Delaunay Triangulation is very complex and time-consuming. This work achieves the objective of constructing a routing graph which is a planar spanner, without requiring the expensive construction of the Delaunay Triangulation, thus saving the node power, an important resource in the ad-hoc network. Moreover, the algorithm guarantees that the total number of messages required to be sent by each node is O(n). This makes the topology easily reconfigurable in case of node motion

    Join-Reachability Problems in Directed Graphs

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    For a given collection G of directed graphs we define the join-reachability graph of G, denoted by J(G), as the directed graph that, for any pair of vertices a and b, contains a path from a to b if and only if such a path exists in all graphs of G. Our goal is to compute an efficient representation of J(G). In particular, we consider two versions of this problem. In the explicit version we wish to construct the smallest join-reachability graph for G. In the implicit version we wish to build an efficient data structure (in terms of space and query time) such that we can report fast the set of vertices that reach a query vertex in all graphs of G. This problem is related to the well-studied reachability problem and is motivated by emerging applications of graph-structured databases and graph algorithms. We consider the construction of join-reachability structures for two graphs and develop techniques that can be applied to both the explicit and the implicit problem. First we present optimal and near-optimal structures for paths and trees. Then, based on these results, we provide efficient structures for planar graphs and general directed graphs

    On Modeling and Analysis of MIMO Wireless Mesh Networks with Triangular Overlay Topology

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    Multiple input multiple output (MIMO) wireless mesh networks (WMNs) aim to provide the last-mile broadband wireless access to the Internet. Along with the algorithmic development for WMNs, some fundamental mathematical problems also emerge in various aspects such as routing, scheduling, and channel assignment, all of which require an effective mathematical model and rigorous analysis of network properties. In this paper, we propose to employ Cartesian product of graphs (CPG) as a multichannel modeling approach and explore a set of unique properties of triangular WMNs. In each layer of CPG with a single channel, we design a node coordinate scheme that retains the symmetric property of triangular meshes and develop a function for the assignment of node identity numbers based on their coordinates. We also derive a necessary-sufficient condition for interference-free links and combinatorial formulas to determine the number of the shortest paths for channel realization in triangular WMNs

    On Mobility Management in Multi-Sink Sensor Networks for Geocasting of Queries

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    In order to efficiently deal with location dependent messages in multi-sink wireless sensor networks (WSNs), it is key that the network informs sinks what geographical area is covered by which sink. The sinks are then able to efficiently route messages which are only valid in particular regions of the deployment. In our previous work (see the 5th and 6th cited documents), we proposed a combined coverage area reporting and geographical routing protocol for location dependent messages, for example, queries that are injected by sinks. In this paper, we study the case where we have static sinks and mobile sensor nodes in the network. To provide up-to-date coverage areas to sinks, we focus on handling node mobility in the network. We discuss what is a better method for updating the routing structure (i.e., routing trees and coverage areas) to handle mobility efficiently: periodic global updates initiated from sinks or local updates triggered by mobile sensors. Simulation results show that local updating perform very well in terms of query delivery ratio. Local updating has a better scalability to increasing network size. It is also more energy efficient than ourpreviously proposed approach, where global updating in networks have medium mobility rate and speed
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