385 research outputs found
Computing connected dominated sets with multipoint relays
International audienceMultipoint relays offer an optimized way of flooding packets in a radio network. However, this technique requires the last hop knowledge: to decide whether or not a flooding packet is retransmitted, a node needs to know from which node the packet was received. When considering broadcasting at IP level, this information may be difficult to obtain. We thus propose a scheme for computing an optimized connected dominating set from multipoint relays. Proof of correctness and simulations are given for all these broadcasting mechanisms
Computing connected dominated sets with multipoint relays
Multipoint relays offer an optimized way of flooding packets in a radio network. However, this technique requires the last hop knowledge: to decide wether or not a flooding packet is retransmitted, a node needs to know from which node the packet was received. When considering broadcasting at IP level, this information may be difficult to obtain. We thus propose a scheme for computing an optimized connected dominating set from multipoint relays. This set allows to efficiently broadcast packets without the last hop information with performances close to multipoint relay flooding
Computing connected dominated sets with multipoint relays
International audienceMultipoint relays offer an optimized way of flooding packets in a radio network. However, this technique requires the last hop knowledge: to decide whether or not a flooding packet is retransmitted, a node needs to know from which node the packet was received. When considering broadcasting at IP level, this information may be difficult to obtain. We thus propose a scheme for computing an optimized connected dominating set from multipoint relays. Proof of correctness and simulations are given for all these broadcasting mechanisms
Maximizing the Probability of Delivery of Multipoint Relay Broadcast Protocol in Wireless Ad Hoc Networks with a Realistic Physical Layer
It is now commonly accepted that the unit disk graph used to model the
physical layer in wireless networks does not reflect real radio transmissions,
and that the lognormal shadowing model better suits to experimental
simulations. Previous work on realistic scenarios focused on unicast, while
broadcast requirements are fundamentally different and cannot be derived from
unicast case. Therefore, broadcast protocols must be adapted in order to still
be efficient under realistic assumptions. In this paper, we study the
well-known multipoint relay protocol (MPR). In the latter, each node has to
choose a set of neighbors to act as relays in order to cover the whole 2-hop
neighborhood. We give experimental results showing that the original method
provided to select the set of relays does not give good results with the
realistic model. We also provide three new heuristics in replacement and their
performances which demonstrate that they better suit to the considered model.
The first one maximizes the probability of correct reception between the node
and the considered relays multiplied by their coverage in the 2-hop
neighborhood. The second one replaces the coverage by the average of the
probabilities of correct reception between the considered neighbor and the
2-hop neighbors it covers. Finally, the third heuristic keeps the same concept
as the second one, but tries to maximize the coverage level of the 2-hop
neighborhood: 2-hop neighbors are still being considered as uncovered while
their coverage level is not higher than a given coverage threshold, many
neighbors may thus be selected to cover the same 2-hop neighbors
Average Size of Unstretched Remote-Spanners
International audienceMotivated by the optimization of link state routing in ad hoc networks, and the concept of multipoint relays, we introduce the notion of remote-spanner. Given an unweighted graph , a remote spanner is a set of links such that for any pair of nodes there exists a shortest path in for which all links in the path that are not adjacent to belong to . The remote spanner is a kind of minimal topology information beyond its neighborhood that any node would need in order to compute its shortest paths in a distributed way. This can be extended to -connected graphs by considering minimum length sum over disjoint paths as distance. In this paper, we give distributed algorithms for computing remote-spanners in order to obtain sparse remote-spanners with various properties. We provide a polynomial distributed algorithm that computes a -connecting unstretched remote-spanner whose number of edges is at a factor from optimal where is the maximum degree of a node. Interestingly, its expected compression ratio in number of edges is O(\frackn\log n) in Erdös-Rényi graph model and O((\frackn)^\frac23) in the unit disk graph model with a uniform Poisson distribution of nodes
An analysis of the lifetime of OLSR networks
The Optimized Link State Routing (OLSR) protocol is a well-known route discovery protocol for ad-hoc networks. OLSR optimizes the flooding of link state information through the network using multipoint relays (MPRs). Only nodes selected as MPRs are responsible for forwarding control traffic. Many research papers aim to optimize the selection of MPRs with a specific purpose in mind: e.g., to minimize their number, to keep paths with high Quality of Service or to maximize the network lifetime (the time until the first node runs out of energy). In such analyzes often the effects of the network structure on the MPR selection are not taken into account. In this paper we show that the structure of the network can have a large impact on the MPR selection. In highly regular structures (such as grids) there is even no variation in the MPR sets that result from various MPR selection mechanisms. Furthermore, we study the influence of the network structure on the network lifetime problem in a setting where at regular intervals messages are broadcasted using MPRs. We introduce the ’maximum forcedness ratio’, as a key parameter of the network to describe how much variation there is in the lifetime results of various MPR selection heuristics. Although we focus our attention to OLSR, being a widely implemented protocol, on a more abstract level our results describe the structure of connected sets dominating the 2-hop neighborhood of a node
Remote spanners: what to know beyond neighbors
International audienceMotivated by the fact that neighbors are generally known in practical routing algorithms, we introduce the notion of remote-spanner. Given an unweighted graph , a sub-graph with vertex set is an \emph{(\a,\b)-remote-spanner} if for each pair of points and the distance between and in , the graph augmented by all the edges between and its neighbors in , is at most \a times the distance between and in plus \b. We extend this definition to -connected graphs by considering minimum length sum over disjoint paths as distance. We then say that an (\a,\b)-remote-spanner is \emph{-connecting }. In this paper, we give distributed algorithms for computing (1+\eps,1-2\eps)-remote-spanners for any \eps>0, -connecting -remote-spanners for any (yielding -remote-spanners for ) and -connecting -remote-spanners. All these algorithms run in constant time for any unweighted input graph. The number of edges obtained for -connecting -remote-spanner is within a logarithmic factor from optimal (compared to the best -connecting -remote-spanner of the input graph). Interestingly, sparse -remote-spanners (i.e. preserving exact distances) with edges exist in random unit disk graphs. The number of edges obtained for (1+\eps,1-2\eps)-remote-spanners and -connecting -remote-spanners is linear if the input graph is the unit ball graph of a doubling metric (distances between nodes are unknown). Our methodology consists in characterizing remote-spanners as sub-graphs containing the union of small depth tree sub-graphs dominating nearby nodes. This leads to simple local distributed algorithms
Heuristics for Network Coding in Wireless Networks
Multicast is a central challenge for emerging multi-hop wireless
architectures such as wireless mesh networks, because of its substantial cost
in terms of bandwidth. In this report, we study one specific case of multicast:
broadcasting, sending data from one source to all nodes, in a multi-hop
wireless network. The broadcast we focus on is based on network coding, a
promising avenue for reducing cost; previous work of ours showed that the
performance of network coding with simple heuristics is asymptotically optimal:
each transmission is beneficial to nearly every receiver. This is for
homogenous and large networks of the plan. But for small, sparse or for
inhomogeneous networks, some additional heuristics are required. This report
proposes such additional new heuristics (for selecting rates) for broadcasting
with network coding. Our heuristics are intended to use only simple local
topology information. We detail the logic of the heuristics, and with
experimental results, we illustrate the behavior of the heuristics, and
demonstrate their excellent performance
Connectivity, Coverage and Placement in Wireless Sensor Networks
Wireless communication between sensors allows the formation of flexible sensor networks, which can be deployed rapidly over wide or inaccessible areas. However, the need to gather data from all sensors in the network imposes constraints on the distances between sensors. This survey describes the state of the art in techniques for determining the minimum density and optimal locations of relay nodes and ordinary sensors to ensure connectivity, subject to various degrees of uncertainty in the locations of the nodes
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