Christos Efstratiou

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In this paper, we describe our experiences of developing and evaluating GUIDE, an intelligent electronic tourist guide. The GUIDE system has been built to overcome many of the limitations of the traditional information and navigation tools available to city visitors. For example, group-based tours are inherently inflexible with fixed starting times and(More)
Studies of automotive traffic have shown that on average 30% of traffic in congested urban areas is due to cruising drivers looking for parking. While we have witnessed a push towards sensing technologies to monitor real-time parking availability, instrumenting on-street parking throughout a city is a considerable investment. In this paper, we present(More)
Sensor networks are typically purpose-built, designed to support a single running application. As the demand for applications that can harness the capabilities of a sensor-rich environment increases, and the availability of sensing infrastructure put in place to monitor various quantities soars, there are clear benefits in a model where infrastructure can(More)
Mobile phones play a pivotal role in supporting ubiquitous and unobtrusive sensing of human activities. However, maintaining a highly accurate record of a user's behavior throughout the day imposes significant energy demands on the phone's battery. In this paper, we present the design, implementation, and evaluation of METIS: an adaptive mobile sensing(More)
Context-awareness can be used to simplify a user’s understanding of, and interaction with, interactive systems. In effect, through adaptation, context-aware systems can migrate complexity away from the user and into the system (or agent). However, the incorporation of context-awareness raises a number of issues. For example, users are required to trust the(More)
Application markets have revolutionized the software download model of mobile phones: third-party application developers offer software on the market that users can effortlessly install on their phones. This great step forward, however, also imposes some threats to user privacy: applications often ask for permissions that reveal private information such as(More)
In this paper we reflect on our long-term experiences of developing, deploying and supporting an experimental digital signage system. Existing public display systems almost always feature a single point of control that is responsible for scheduling content for presentation on the network and provide sophisticated mechanisms for controlling play-out timing(More)
Mobile applications are required to operate in environments characterised by change. More specifically, the availability of resources and services may change significantly during a typical period of system operation. As a consequence, adaptive mobile applications need to be capable of adapting to these changes to ensure they offer the best possible level of(More)
SMS had been demonstrated only two years previously; and the first Bluetooth specification would not arrive for another three years. Regrettably, we were forced to remove one of our FLUMP stations from a public area after a short time because of fire safety concerns—our first hint that deployment “in the wild” brought its own unique set of challenges. From(More)
The increasing popularity of location based social services such as Facebook Places, Foursquare and Google Latitude, solicits a new trend in fusing social networking with real world sensing. The availability of a wide range of sensing technologies in our everyday environment presents an opportunity to further enrich social networking systems with(More)