Catálogo de publicaciones - libros

Due to their small form factor and modest energy budget, individual sensors are not expected to be GPS-enabled. Moreover, in most applications, exact geographic location is not necessary, and all that the individual sensors need is a coarse-grain location awareness. The task of acquiring such a coarse-grain location awareness is referred to as training. In this paper, a scalable energy-efficient training protocol is proposed for massively-deployed sensor networks, where sensors are initially anonymous and unaware of their location. The training protocol is lightweight and simple to implement; it is based on an intuitive coordinate system imposed onto the deployment area which partitions the anonymous sensors into clusters where data can be gathered from the environment and synthesized under local control.

One of the most critical factors for lifetime and operability of ad-hoc and sensor networks is the limited amount of available energy. To this respect, minimizing the interference in the network has certainly a positive effect, since of the reduced number of conflicting transmissions. However, quite surprisingly, only few theoretical results are known about the possibility to maintain the interference low while at the same time guaranteeing certain network connectivity properties. In this paper, we give a contribution in this direction, and we study several network interference measures with respect to the symmetric connectivity, the strong connectivity, and the broadcast connectivity predicate.

In particular, we show that the probably most prominent interference problem, namely that of minimizing the interference experienced by any node in the network, is hard to approximate within better than a logarithmic factor, unless NP admits slightly superpolynomial time algorithms, for any of the above connectivity predicates. On a positive side, we show that any approximation algorithm for the problem of minimizing the total range assigned to the nodes in order to guarantee any of the above connectivity predicates, can be transformed, by maintaining the approximation ratio, into an approximation algorithm for the problem of minimizing the interference experienced by all the nodes in the network.

Emergency Preparedness is one of the most appealing classes of applications for context-aware wireless sensor networks (WSN). In such environments, contexts can be captured and interpreted in the WSN application layer to help preventing, fighting, rescuing and checking against fire, explosions, leaking of toxic gases etc. In this paper, we show a Wireless Actor and Sensor Network (WASN) that can be used to interpret simple and complex contexts. We present an efficient technique that make use of actors to aggregate sensor events, eliminate ambiguities and redundancy and realize context interpretations. Each actor of the WASN is configured with rules that are determined by the application in the network configuration phase. Context information is exchanged among actors and sink(s) of the WASN through the publish/subscribe paradigm based on specific topics. We present a set of simulation of experiments to evaluate the performance of our protocols for wireless sensor networks.

We propose an algorithm for coordinating access to a shared broadcast channel in an ad hoc network of unknown size . We reduce the runtime necessary to self-organize access to the channel over the previous algorithm of Cai, Lu and Wang. The runtime of this algorithm is (), our work is to improve the constant factors involved. Apart from experimental evidence of algorithm quality, we provide a rigorous probabilistic analysis of its behavior.

In this work we present a protocol for securing communication trees in sensor networks. Communication trees can be used in a number of ways; to broadcast commands, to aggregate information or to route messages in the network. Broadcast trees are necessary for broadcasting information such as commands of maintenance packets from the base station to all sensors in the network. Aggregation trees are used in a complementary way to aggregate information collected by individual nodes so that meaningful summaries are presented to the base station, thus saving energy from unnecessary retransmissions. Alternatively, trees are constructed by many routing protocols, hence the security of these trees is important to prevent against many routing attacks.

In this work we demonstrate how to establish such trees in a secure and authenticated way. Our protocol is simple and efficient and furthermore enables changes to the tree structure due to failure of nodes or addition of new ones. Finally, it is resistant to a host of attacks that can be applied to sensor networks.

We consider the problem in a ring for a network of identical sensors: starting from some initial random placement in the ring, the sensors in the network must move, in a purely decentralized and distributed fashion, so to reach in finite time a state of static equilibrium in which they evenly cover the ring. A self-deployment algorithm is if within finite time the sensors reach a static configuration: the distance between any two consecutive sensors along the ring is the same, ; the self-deployment algorithm is - if the distance between two consecutive sensors is between − and + .

We prove that self-deployment is if the sensors do not share a common orientation of the ring.

We then consider the problem in an oriented ring. We prove that if the sensors know the desired final distance , then self-deployment is possible. Otherwise, we present another protocol based on a very simple strategy and prove that it is -approximate for any chosen > 0.

Our results show that a of the ring is an important computational and complexity factor for a network of mobile sensors operating in a ring.

We consider the problem of topology control of a wireless ad-hoc network on a given set of points in the plane, where we aim to minimize the maximum interference by assigning a suitable transmission radius to each point. By using computational geometric ideas and -net theory, we attain an bound for the maximum interference where Δ is the interference of a uniform-radius ad-hoc network. This generalizes a result given in [8] for the special case of highway model (i.e., one-dimensional problem) to the two-dimensional case. We also give a method based on quad-tree decomposition and bucketing that has another provable interference bound in terms of the ratio of the minimum distance to the radius of a uniform-radius ad-hoc network.

Ad hoc sensor networks consist of large number of wireless sensors that communicate with each other in the absence of a fixed infrastructure. Fast self-reconfiguration and power efficiency are very important property on any sensor network management. The clustering problem consists in partitioning network nodes into groups called clusters, thus giving at the network a hierarchical organization. Clustering increases the scalability and the energy efficiency of communication among the sensors. A self-stabilizing algorithm, regardless of the initial system state, converges to a set of states that satisfy the problem specification without external intervention. Due to this property, self-stabilizing algorithms are adapted highly dynamic networks. In this paper we present a Self-stabilizing Clustering Algorithm for Ad hoc sensor network. Our algorithm adapts faster than other algorithms to topology changes.

Given a wireless Ad-Hoc network modeled as a unit disk graph in the plane, we present a localized distributed algorithm that constructs a bounded degree planar power spanner of with a bounded stretch factor. More specifically, for an integer parameter ≥8 and a power exponent constant ∈[2,5], our algorithm constructs a planar power spanner for the network of degree bounded by + 5 and a stretch factor bounded by 1 + 2 sin (/). This significantly improves the previous best results in the literature by Song et al..

The present paper deals with communication in random geometric topologies; in particular, we model modern wireless ad hoc networks by random geometric topologies. The paper has two goals: the first is to implement the network power control mechanism extended by several wireless engineering features and to use the model to assess communicational properties of two typical random geometric topologies known from the literature in real-life conditions. The second goal is to suggest a modification of the “LowDegree” algorithm (one of the two studied topologies), which preserves excellent power requirements of the model, but matches the performance of the standard “UnitDisk” algorithm in terms of higher total network throughput.