Sergio Ilarri

Location-dependent query processing: Where we are and where we are heading

The continuous development of wireless networks and mobile devices has motivated an intense research in mobile data services. Some of these services provide the user with context-aware information. Specifically, location-based services and location-dependent queries have attracted a lot of interest. In this article, the existing literature in the field of location-dependent query processing is reviewed. The technological context (mobile computing) and support middleware (such as moving object databases and data stream technology) are described, location-based services and location-dependent queries are defined and classified, and different query processing approaches are reviewed and compared.

Comparison and Performance Evaluation of Mobile Agent Platforms

Mobile agents are considered a very interesting technology to develop applications for mobile, pervasive, and distributed computing. Thus, they present a combination of unique features, such as their autonomy and capability to move to remote computers to process data there and save remote communications. Many mobile agent platforms have been developed since the late nineties. While some of them have been abandoned, others continue releasing new versions that fix bugs detected or offer new interesting features. Moreover, other new platforms have appeared in the last few years. So, a common problem when one wants to benefit from mobile agent technology to develop distributed applications is the decision about which platform to use. In this paper, we provide an up-to-date evaluation of existing mobile agent platforms. We compare them qualitatively and evaluate their performance.

Location-dependent queries in mobile contexts: distributed processing using mobile agents

With the current advances of mobile computing technology, we are witnessing an explosion in the development of applications that provide mobile users with a wide range of services. In this paper, we present a system that supports distributed processing of continuous location-dependent queries in mobile environments. The system that we propose presents the following main advantages: 1) it is a general solution for the processing of location-dependent queries in scenarios where not only the users issuing queries, but also other interesting objects can move; 2) it performs an efficient processing of these queries in a continuous way; 3) it is especially well adapted to environments where location data are distributed in a network and processing tasks can be performed in parallel, allowing a high scalability; and 4) it optimizes wireless communications. We use mobile agents to carry the processing tasks wherever they are needed. Thus, agents are in charge of tracking the location of interesting moving objects and refreshing the answer to a query efficiently. We evaluate the usefulness of the presented proposal showing that the system achieves a good precision and scales up well

Using cooperative mobile agents to monitor distributed and dynamic environments

Monitoring the changes in data values obtained from the environment (e.g., locations of moving objects) is a primary concern in many fields, as for example in the pervasive computing environment. The monitoring task is challenging from a double perspective. First and foremost, the environment can be highly dynamic in terms of the rate of data changes. Second, the monitored data are often not available from a single computer/device but are distributed; moreover, the set of data providers can change along the course of time. Therefore, obtaining a global snapshot of the environment and keeping it up-to-date is not easy, especially if the conditions (e.g., network delays) change. In this article, a decentralized, loose, and fault-tolerant monitoring approach based on the use of mobile agents is described. Mobile agents allow easy tracking of the involved computers, carrying the monitoring tasks to wherever they are needed. A deadline-based mechanism is used to coordinate the cooperative agents, which strive to perform their continuous tasks in time while considering data as recent as possible, constantly adapting themselves to new environmental conditions (changing communication and processing delays). This approach has been successfully used in a real environment and experiments were carried out to prove its feasibility and benefits.

A Content-Based Dissemination Protocol for VANETs: Exploiting the Encounter Probability

This paper focuses on intelligent transportation systems and, more precisely, on intervehicle ad hoc networks. A vehicular ad hoc network (VANET) is a highly dynamic network as the vehicles communicate using short-range wireless communications and can move very quickly. Thus, for example, we can only rely on short interactions between vehicles to exchange information about relevant events. In this paper, we describe in detail a dissemination protocol that vehicles can use to share information by using vehicle-to-vehicle communications. The dissemination approach considers the relevance of the data, represented by what we call encounter probability, to decide when a rediffusion is needed. The protocol is able to disseminate data about any type of event in the network (e.g., available parking spaces, accidents or obstacles in the road, information about moving objects such as emergency vehicles that should get the right of way, etc.) by setting appropriate weights for the different factors that affect the computation of the encounter probability. An extensive experimental evaluation with different types of events shows the interest of the proposal: The vehicles receive the relevant messages in time, and the network overload is limited.

A cooperative reservation protocol for parking spaces in vehicular ad hoc networks

By exchanging events in a vehicular ad hoc network, drivers can receive interesting information while driving. For example, they can be informed of available parking spaces in their vicinity. Obviously, a suitable protocol is needed to disseminate the events efficiently within the area where they are relevant. Moreover, in such a competitive context where each vehicle may be interested in the resource, it is crucial not to broadcast that resource to each driver in the vicinity. Otherwise, those drivers would waste time trying to reach a parking space and only one of them would be satisfied, which would lead to a poor satisfaction in the system. To solve this problem, we detail in this paper a reservation protocol that efficiently allocates parking spaces in vehicular ad hoc networks and avoids the competition among the vehicles. We have integrated our protocol within VESPA, a system designed for vehicles to share information in VANETs.

SPRINGS: a scalable platform for highly mobile agents in distributed computing environments

In the last decade, mobile agents have arisen as a promising paradigm to build distributed and mobile computing applications. However, mobile agents have not been massively adopted. One of the reasons could be that some issues have yet to be solved to increase the confidence of developers. Thus, scalability problems sometimes arise in applications with a high number of mobile agents when calls and trips happen very frequently. In this paper we present SPRINGS, a novel Java-based mobile agent system which is scalable, flexible, and easy to use. Our work has been motivated by our experience with mobile agents in several research projects. We focus on scalability issues and efficient maintenance of location-independent agent references in dynamic scenarios where agents communicate and travel frequently among computers. We have obtained encouraging performance results through an extensive set of experiments. Moreover, our tests show that SPRINGS achieves a degree of concurrency that other well-known platforms cannot reach

Semantics in Location-Based Services [Guest editor's introduction]

A dvances in wireless networks and mobile devices have motivated an intensive research effort in mobile computing and mobile data services. The goal is to provide users with anywhere, anytime connectivity to the Internet and access to services that are valuable depending on users’ context. One of the most interesting context factors is user location. Thus, context-awareness, and particularly location-based services (LBSs),1 have attracted great interest. Moreover, rapid progress in developing Semantic Web standards, tools, and techniques (see www.w3.org/2001/sw/), including applications that are rich in spatial and temporal dimensions,2 and the vision of the geospatial Semantic Web3 enable the development of more intelligent LBSs.

Dissemination of information in inter-vehicle ad hoc networks

This paper focuses on intelligent transportation systems and more precisely on inter-vehicle ad hoc networks. Such networks are highly dynamic due to the movements of the vehicles and the short range of the wireless communications. Thus, for example, we can only rely on short interactions between the vehicles to exchange data about relevant events. We propose a new dissemination technique for vehicles to share information using V2V communications. Our goal is to make possible the exchange of information between vehicles when they encounter each other, taking into account the relevance of the data to the drivers. The originality of our proposal is that it relies on an encounter probability to disseminate data about any type of event (e.g., available parking spaces, obstacles in the road, information relative to the coordination of vehicles in emergency situations, etc.) in the network.

Sharing with caution: Managing parking spaces in vehicular networks

By exchanging events in a vehicular ad hoc network VANET, drivers can receive interesting information while driving. For example, they can be informed of available parking spaces in their vicinity. A suitable protocol is needed to disseminate the events efficiently within the area where they are relevant. Moreover, in such a competitive context where each vehicle may be interested in a resource, it is crucial not to communicate that resource to each driver in the vicinity. Otherwise, those drivers would waste time trying to reach a parking space and only one of them would be fulfilled, which would lead to a poor satisfaction in the system. To solve this problem, we detail in this paper a reservation protocol that efficiently allocates parking spaces in vehicular ad hoc networks and avoids the competition among the vehicles. We have integrated our protocol within VESPA, a system that we have designed for vehicles to share information in VANETs. An experimental evaluation is provided, which proves the usefulness and benefits of our reservation protocol in both parking lots and urban scenarios. Besides, we present an in-depth study of the state of the art on this topic, that shows the interest and the originality of our approach.