We present an efficient distributed data structure, called the D-SPANNER, for maintaining proximity information among communicating mobile nodes. The D-SPANNER is a kinetic sparse graph spanner on the nodes that allows each node to quickly determine which other nodes are within a given distance of itself, to estimate an approximate nearest neighbor, and to perform a variety of other proximity related tasks. A lightweight and fully distributed implementation is possible, in that maintenance of the proximity information only requires each node to exchange a modest number of messages with a small number of mostly neighboring nodes. The structure is based on distance information between communicating nodes that can be derived using ranging or localization methods and requires no additional shared infrastructure other than an underlying communication network. Its modest requirements make it scalable to networks with large numbers of nodes.

Abstract — Warehouses must maintain a number of spatial constraints concerning the safe handling of hazardous materials. In this paper, we address the problem of automated monitoring of spatial constraints as pallets are moved on forklifts by human operators. We propose using small, self-contained localizing sensor packages mounted on pallets. We consider two architectures: 1) a global architecture where sensors are mounted on pallets and on the warehouse ceiling, and 2) a local architecture where sensors are located only on the pallets. We formally model the problem for a warehouse environment where sensors can be installed on the pallets or on the ceiling. We also report on preliminary experimental results on the accuracy of constraint violation detection as a function of inter-sensor distance and angle. I.

Abstract. Location information of mobile users is very sensitive with regard to privacy. This is especially true for proactive location based services (LBSs) where users are continuously tracked. Effective privacy enhancing technologies for these services are still an open field of research. In this paper, we focus on proactive location based community services (PLBCSs), such as mobile gaming or buddy tracking. Instead of relating the spatial position of users to fixed real-world entities, like e.g. tourist sights in a navigation service, in PBLCSs, the focus is on a user’s spatial relation to other users or virtual entities. In the paper, we discuss why existing privacy mechanism for LBSs are not well suited for PLBCSs. We also present initial ideas for a novel anonymization technique, where location coordinates are obfuscated by a key shared among community members before they are emitted to a PLBCS. Like this, statistical attacks on pseudonym-associated can be avoided while calculations of spatial relations between the entities can be done with unchanged accuracy. 1. Proactive Location Based Community Services (PLBCSs) and Privacy In ubiquitous computing environments the need for privacy amplifies, as ubiquity of computing leads to reduced user control over collected data [Lang01]. For proactive LBSs this is especially true. Although users agree to be tracked in general, location information is collected continuously and

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 locationdependent queries are defined and classified, and different query processing approaches are reviewed and compared.

Given a set of users, their friend relationships, and a distance threshold per friend pair, the proximity detection problem is to find each pair of friends such that the Euclidean distance between them is within the given threshold. This problem plays an essential role in friend-locator applications and massively multiplayer online games. Existing proximity detection solutions either incur substantial location update costs or their performance does not scale well to a large number of users. Motivated by this, we present a centralized proximity detection solution that assigns each mobile client with a mobile region. We then design a self-tuning policy to adjust the radius of the region automatically, in order to minimize communication cost. In addition, we analyze the communication cost of our solutions, and provide valuable insights on their behaviors. Extensive experiments suggest that our proposed solution is efficient and robust with respect to various parameters. 1.

In this chapter we study the problems of data dissemination and query routing in mobile peer-to-peer networks. We provide a taxonomy and discussion of existing literature, spanning overlay topologies, query routing, and data propagation. We proceed by proposing content-driven routing and adaptive data dissemination algorithms for intelligently routing search queries in a peer-to-peer network that supports mobile users. In our mechanism nodes build content synopses of their data and adaptively disseminate them to their most appropriate peers. Based on the content synopses, a routing mechanism is being built, to forward the queries to those peers that have a high probability of providing the desired results. We provide an experimental evaluation of different dissemination strategies that shows that content-driven routing and adaptive data dissemination is highly scalable and significantly improves resource usage.

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 locationdependent queries are defined and classified, and different query processing approaches are reviewed and compared.