Catálogo de publicaciones - libros

A wireless ad hoc network is a collection of wireless nodes that can dynamically self-organize into an arbitrary and temporary topology to form a network without necessarily using any pre-existing infrastructure. These characteristics make ad hoc networks well suited for military activities, emergency operations, and disaster recoveries. Nevertheless, as electronic devices are getting smaller, cheaper, and more powerful, the mobile market is rapidly growing and, as a consequence, the need of seamlessly internetworking people and devices becomes mandatory. New wireless technologies enable easy deployment of commercial applications for ad hoc networks. The design of an ad hoc network has to take into account several interesting and difficult problems due to noisy, limited-range, and insecure wireless transmissions added to mobility and energy constraints. This paper presents an overview of issues related to medium access control (MAC), routing, and transport in wireless ad hoc networks and techniques proposed to improve the performance of protocols. Research activities and problems requiring further work are also presented. Finally, the paper presents a project concerning an ad hoc network to easily deploy Internet services on low-income habitations fostering digital inclusion.

This paper presents a new approach to assign trust levels in ad hoc networks. Our system is inspired by the human concept of trust. The trust level considers the recommendation of trustworthy neighbors and their own experience. For the recommendation computation, we take into account not only the trust level, but also its accuracy and the relationship maturity. We also propose the Recommendation Exchange Protocol (REP), which minimizes the number of exchanged messages. The results show the efficacy of the system and the influence of main parameters.

Wireless networks play a major role in allowing the deployment of ubiquitous distributed systems. In these networks, service discovery should not only allow finding available networked services, but should also take into account the physical proximity of the entities requesting these services. However, physical proximity is not a sufficient criteria for service search and selection, as close attention should be paid to privacy issues. In this paper we present the design issues that should be considered in order to properly support service discovery based on the physical location of clients; these issues are taken into account for the proposal of an architecture for context-aware distributed systems that consider privacy concerns.

Service discovery allows the interaction between network nodes to cooperate in activities or to share resources in client-server, multi-layer, as well as in peer-to-peer architectures. Ad hoc networks pose a great challenge in the design of efficient mechanisms for service discovery. The lack of infrastructure along with node mobility makes it difficult to build robust, scalable and secure mechanisms for ad hoc networks. This paper proposes a scalable service discovery architecture based on directory nodes organized in an overlay network. In the proposed architecture, directory nodes are dynamically created with the aim of uniformly covering the entire network while decreasing the query latency for a service (QoS) and the number of control messages for the sake of increased scalability.

This paper addresses the performance of geographical routing protocol in wireless networks, where only few nodes possess self-locating capability such as GPS. To be able to apply end-to-end geographical routing protocols, it is necessary every node know their position coordinates. We propose a method to infer such positioning information to any node, based only on connectivity and localization information obtained from the neighborhood. Three metrics are used to evaluate the performance of such a scheme: the density of useful nodes for geographical routing protocol, the reachability and the path length.

This paper introduces and analyzes a field estimation scheme for wireless sensor networks. Our scheme imitates the response of living beings to the surrounding events. The sensors define their periphery of attention based on their own readings. Readings differing from the expected behavior are considered events of interest and trigger the data transmission to the sink. The presented scheme is evaluated with real-site-collected data and the tradeoff between the amount of data sent to the sink and the reconstruction error is analyzed. Results show that significant reduction in the data transmission and, as a consequence, in the energy consumption of the network is achievable while keeping low the average reconstruction error.

Most of the current wireless sensor networks are built for specific applications, with a tight coupling between them and the underlying communication protocols. We present a more flexible architectural approach for building WSNs, in which application-specific features are decoupled from the underlying communication infrastructure, although affecting the network behavior. We propose a framework based on Web technologies that provides a standard interface for accessing the network and configurable service components tailored to meet different application requirements, while optimizing the network scarce resources. Also, a set of ontologies is defined as part of the framework for representing shared knowledge of the WSN domain.

Because of the remote nature and the size of sensor nodes, they rely on limited battery energy that cannot be replenished in many applications. Thus, low power consumption technology is a major issue in wireless sensor networks in order to prolong system lifetime. In this paper, we propose to maximize energy efficiency in wireless sensor networks using optimal packet length in terms of power management and channel coding. The use of power management cannot improve energy efficiency, but it saves a lot of energy because the transceiver is turned off while it is not used. Also, we evaluate optimal packet length without power management in such that the energy efficiency can be maximized. Finally, we show that the BCH code for channel coding can improve energy efficiency significantly compared to the convolutional code.

A simple and fair proposal to improve the performance of the IEEE 802.11e standard is presented in this paper. Our proposal is accomplished by means of increasing the priority of those queues that have not been able to transmit during certain period of time, depending on the elapsed time waiting to transmit. Results show that this proposal improves the performance of wireless networks using IEEE 802.11e EDCF since low priority queues reduce their waiting time to access the channel and high priority queues are not degraded.

Mobile computing applications are required to operate in environments in which the availability for resources and services may change significantly during system operation. As a result, mobile computing applications need to be capable of adapting to these changes to offer the best possible level of service to their users. However, traditional middleware is limited in its capability of adapting to environment changes and different users requirements. Computational Reflection and Aspect Oriented Programming paradigms have been used in the design and implementation of adaptive middleware architectures. In this paper, we propose two adaptive middleware architectures, one based on reflection and other based on aspects, which can be used to develop adaptive mobile applications. The reflection based architecture is compared to an aspect oriented based architecture from a quantitative perspective. The results suggest that middleware based on Aspect Oriented Programming can be used to build mobile adaptive applications that require less processor running time and more memory space than Computational Reflection while producing code that is easier to comprehend and modify.