Portrait of Dr Christos Efstratiou

Dr Christos Efstratiou

Lecturer in Ubiquitous Computing


Christos Efstratiou is a Lecturer at the School of Engineering and Digital Arts, University of Kent. He received his Ph.D. from Lancaster University, UK. He has been a Senior Research Associate at the University of Cambridge, a Research Associate at Lancaster University and a visiting researcher at Sony Electronics Distributed Systems Lab in San Jose. 

His early work focused on the support for adaptive and context-aware applications in mobile environments. More recently, he has been actively involved in research projects in the areas of pervasive computing, and mobile and embedded sensing. In his current work, he is targeting the areas of social and people-centric sensing and the challenges emerging by the fusion of mobile phone sensing, with sensing technologies embedded in the environment.

​Recent professional service

  • Organizing Committee Member for the Int. ACM Workshop on Mobile Computing Systems and Applications (HOTMOBILE 2014)
  • Program Committee Member for the IEEE Pervasive Computing and Communication Conference (PerCom 2014)
  • Program Committee Member for the Int. Workshop on Pervasive Urban Crowdsensing Architecture and Applications (PUCAA 2013)
  • Program Committee Member for the Int. ACM Workshop on Wireless Network Testbeds, Experimental evaluation and Characterization (WiNTEC 2013)
  • Program Committee Member for 5th ACM HotPlanet Workshop (HOTPLANET 2013)
  • Program Committee Member for the IEEE International Symposium on Mobile Cloud, Computing and Service Engineering (MobileCloud 2013)
  • Organizing Committee Member for the Int. ACM Workshop on Mobile Computing Systems and Applications (HOTMOBILE 2013)
  • Program Committee Member for the IEEE Pervasive Computing and Communication Conference (PerCom 2013)

Research interests

Ubiquitous computing, mobile computing, social computing, internet of things, wireless sensor networks.

Current projects

Epilepsy Networks

One of the challenges in the delivery of high quality care to people with epilepsy is the accurate collection and analysis of information about their condition, and possible seizures, throughout their daily life. The aim of the project is to develop a platform for connecting patients, family, hospital teams and community staff around an innovative, shared digital record that includes input from the patients and their families. The objective is to link sources of information scattered through the community of health practitioners and family, along with new sources captured through smartphone sensing and social tracking, into a cohesive dataset which is secure but accessible at the point of care, wherever that is provided. The project will deliver a means for patients and their families to record important aspects of their condition electronically, using smartphones and wearable technologies, and prospectively share this with their doctors so that potential problems can be picked up before they escalate to an emergency. Moreover, the project aims to include a link to local guidelines and decision support tools to ensure that non-specialist healthcare professionals are supported in making care seamless. 

Fusion of mobile phone sensing and sensors in the environment

The availability of a wide range of sensing technologies in our everyday environment presents an opportunity to enrich mobile sensing applications with fine-grained real-world sensing. The fusion of both mobile and sensing in the environment offers opportunities to achieve better accuracy for people-centric applications, as well as new strategies for reducing energy consumption on mobile devices. However, the introduction of passive sensing into people-centric sensing applications disrupts the traditional, user-initiated input to sensing services, raising both privacy and acceptability concerns.

Social interactions in the workplace

In many work environments, serendipitous interactions between members of different groups may lead to enhanced productivity, collaboration and knowledge dissemination. In this work the aim is to explore the use of wireless sensing technologies to capture social interaction in workplaces. Further analysis of the real social network of face-to-face interactions can reveal new insights on how social ties are created in a working environment, and how teams and individuals can collaborate and influence each other.

Wireless Sensing in Construction

Exploring the technical challenges of building wireless sensor networks for structural monitoring. The aim is to desing a reliable system for wireless sensing, reliying on the use of open standards such as 6LoWPAN that can facilitate interoperability and integration of a diverce range of sensing devices. Current work involves the deployment of a 6LoWPAN based sensor network in an old Post-Office tunnel in London, monitoring the displacement of the rings of metal that constitute the tunnel.

FRESNEL: Federated Secure Sensor Network Laboratory

With FRESNEL we aim to build a large scale federated sensor network framework with multiple applications sharing the same resources. We want to guarantee a reliable intra-application communication as well as a scalable and distributed management infrastructure. Orthogonally, privacy and application security should also be maintained.

Past Projects

  • NEMO: Networked Embedded Models and Memories of Physical Work Activity
  • e-Campus: A Research Network of Public Displays
  • GUIDE: Context-Aware Electronic Tourist Guide



  • Nawaz, S., Efstratiou, C. and Mascolo, C. (2016). Smart Sensing Systems for the Daily Drive. IEEE Pervasive Computing [Online]:39-43. Available at: http://www.dx.doi.org/10.1109/MPRV.2016.22.
    When driving, you might sometimes wonder, "Are there any disruptions on my regular route that might delay me, and will I be able to find a parking space when I arrive?" Two smartphone-based prototype systems can help answer these questions. The first is ParkSense, which can be used to sense on-street parking-space occupancy when coupled with electronic parking payment systems. The second system can sense and recognize a user's repeated car journeys, which can be used to provide personalized alerts to the user. Both systems aim to minimize the impact of sensing tasks on the device's lifetime so that the user can continue to use the device for its primary purpose. This department is part of a special issue on smart vehicle spaces.
  • Efstratiou, C., Rachuri, K. and Das, S. (2015). IEEE PerCom 2015. IEEE Pervasive Computing [Online] 14:84-88. Available at: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7140687.
    The 2015 IEEE International Conference on Pervasive Computing and Communications (PerCom 2015) was held in Saint Louis, Missouri. With 13 years of history, PerCom has become one of the premier venues for ubiquitous computing research. Several cutting-edge workshops ran in parallel on March 23rd and 27th, while the main conference took place March 24–26th as a single-track event.
  • Rachuri, K. et al. (2014). Smartphone sensing offloading for efficiently supporting social sensing applications. Pervasive and Mobile Computing [Online] 10:3-21. Available at: http://dx.doi.org/10.1016/j.pmcj.2013.10.005.
    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 work, we investigate a new approach that can lead to significant energy savings for mobile applications that require continuous sensing of social activities. This is achieved by opportunistically offloading sensing to sensors embedded in the environment, leveraging sensing that may be available in typical modern buildings (e.g., room occupancy sensors, RFID access control systems).

    In this article, we present the design, implementation, and evaluation of METIS: an adaptive mobile sensing platform that efficiently supports social sensing applications. The platform implements a novel sensor task distribution scheme that dynamically decides whether to perform sensing on the phone or in the infrastructure, considering the energy consumption, accuracy, and mobility patterns of the user. By comparing the sensing distribution scheme with sensing performed solely on the phone or exclusively on the fixed remote sensors, we show, through benchmarks using real traces, that the opportunistic sensing distribution achieves over 60% and 40% energy savings, respectively. This is confirmed through a real world deployment in an office environment for over a month: we developed a social application over our frameworks, that is able to infer the collaborations and meetings of the users. In this setting the system preserves over 35% more battery life over pure phone sensing.
  • Friday, A., Davies, N. and Efstratiou, C. (2012). Reflections on Long-Term Experiments with Public Displays. IEEE Computer 45:34-41.
  • Büscher, M. et al. (2009). Intelligent Mobility Systems: Some Socio-technical Challenges and Opportunities. Communications Infrastructure. Systems and Applications in Europe [Online] 16:140-152. Available at: http://dx.doi.org/10.1007/978-3-642-11284-3_15.
    Analysis of socio-technical challenges and opportunities around contemporary mobilities suggests new interpretations and visions for intelligent transport systems. Multiple forms of intelligence are required (but not easily compatible), transport is too narrow a term, and innovation results in new socio-technical systems. An exploration of cumulative, collective and collaborative aspects of mobility systems, allows us to sketch challenges and opportunities in relation to practices of collaboration, communication and coordination, literacies for creativity, comfort and control, citizenship and (lack of) a sense of crisis, concluding with a discussion of methodological implications.
  • Cheverst, K. et al. (2001). Using Context as a Crystal Ball: Rewards and Pitfalls. Personal and Ubiquitous Computing [Online] 5:8-11. Available at: http://dx.doi.org/10.1007/s007790170020.
    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 behaviour of the system’s intelligence and this requires the system to have predictable behaviour and the ability to successfully and consistently preempt the user’s goal. Unfortunately, the agent may incorrectly preempt the user’s goal, owing to either flawed intelligence or to incorrect or out-of-date contextual information. In such circumstances the user is likely to feel frustration because the system will either appear overly prescriptive or, worse still, present incorrect results. This paper considers these issues, a number of which are described in anecdotal form, based on our experiences in developing and evaluating the context-aware GUIDE system
  • Costaridou, L. et al. (1997). A Layered Architecture for Computer-based simulation supporting skills learning: an X-ray imaging paradigm. Medical Informatics [Online] 22:165-177. Available at: http://dx.doi.org/10.3109/14639239709010889.
    Simulation is characterized by strong learning potential, providing the basis for a new category of systems, the simulation-based learning systems. To strengthen the learning potential of these systems, models are needed not only of the actual system being imitated, but also of the operational expertise required to carry out manipulations of the simulated system, inherently linked to learning. In this paper, an architecture is reported aimed at supporting the organization of multimodal simulation resources to induce skills learning. This architecture is based on distinct layers, allowing independent representation of learning and simulation components. Its applicability has been demonstrated by means of a paradigm, including simulation of X-ray imaging procedure, as well as authoring of learning scenarios pertaining to such procedures.

Book section

  • Buscher, M. et al. (2012). Connected, computed, collective: Smart Mobilities. in: Grieco, M. and Urry, J. eds. Mobilities: new perspectives on transport and society. Ashgate, pp. 135-158.
    The 'smart' in 'Smart Transport' usually refers to technologies, not people. From cars designed to be 'stackable', through signs that monitor parking spaces, to 'automatic cruise control' systems that 'intelligently' control distances through vehicle-to-vehicle and vehicle-to-infrastructure communication: technologies are key to smart transport. And it is true, people — armoured with status symbol cars and stuck in traffic — often do not behave intelligently, raging at other drivers and pedestrians, taking risks that endanger themselves and others. However, underestimating human intelligence could be a damaging oversight and missed opportunity for transport designers. In this chapter we examine several related aspects of human sense-making practices on the move and explore how these could be productively integrated with smart transport. Starting with a comparison of a 'view from above' and a 'view from on the ground', key aspects of the social logics of our mobile societies become visible. Then, new technologies are already an integral part of the social organisation of mobilities — with some socio-technical innovations that form a kind of parallel universe to the intelligent transport solutions envisaged by engineers and traffic planners. We discuss such 'alternate smart mobilities' through some utopian visions of 'collective intelligence' (Levy 1997) and its more mundane manifestations, including micro-coordination and an emergent digital economy of mobilities, based on crowdsourcing, community sensing, and data mashups. These 'bottom-up' innovations could come together productively with the pervasive 'qualculation' (Thrift 2004) that underpins traffic shaping and other engineering and design efforts around 'intelligent transport systems' (ITS) (COM 2008). Moreover, such a convergence of social and technological innovation could counteract the threat of 'Orwellian' surveillance that is part of a potentially Faustian bargain for more efficiency, convenience, sustainability and security in transport (Dennis and Urry 2009). We conclude with suggestions for mixed mobile research methods that can inform innovation.

Conference or workshop item

  • Nicholls, B. et al. (2017). Swallowing detection for game control: using skin-like electronics to support people with dysphagia. in: IEEE PerCom Workshop on Pervasive Health Technologies. IEEE. Available at: http://dx.doi.org/10.1109/PERCOMW.2017.7917598.
    In this paper, we explore the feasibility of developing a sensor-driven rehabilitation game for people suffering from dysphagia. This study utilizes the skin-like electronics for unobtrusive, comfortable, continuous recording of surface electromyograms (EMG) during swallowing and use them for driving game-based, user-controlled feedback. The experimental study includes the development and evaluation of a real-time swallow detection algorithm using skin-like sensors and a game-based human-computer interaction. The user evaluations support the ease of use of the skin-like electronics as a motivational tool for people with dysphagia.
  • Baker, J. and Efstratiou, C. (2017). Next2Me: Capturing Social Interactions through Smartphone Devices using WiFi and Audio signals. in: EAI International Conference on Mobile and Ubiquitous Systems: Computing, Networking and Services (MobiQuitous 2017). ACM, pp. 412-421. Available at: http://dx.doi.org/10.1145/3144457.3144500.
    Typical approaches in detecting social interactions consider the use of co-location as a proxy for real-world interactions. Such approaches can underperform in challenging situations where multiple social interactions can occur in close proximity to each other. In this paper, we present a novel approach to detect co-located social interactions using smartphones. Next2Me relies on the use of WiFi signals and audio signals to accurately distinguish social groups interacting within a few meters from each other. Through a range of real-world experiments, we demonstrate a technique that utilises WiFi fingerprinting, along with sound fingerprinting to identify social groups. Experimental results show that Next2Me can achieve a precision of 88% within noisy environments, including smartphones that are placed in users’ pockets, whilst maintaining a very low energy footprint (<3% of battery capacity per day).
  • Bai, L., Efstratiou, C. and Ang, C. (2016). weSport: Utilising Wrist-Band Sensing to Detect Player Activities in Basketball Games. in: WristSense 2016: Workshop on Sensing Systems and Applications Using Wrist Worn Smart Devices (co-located with IEEE PerCom 2016).. Available at: https://sites.google.com/site/wristsenseworkshop2016/.
    Wristbands have been traditionally designed to track the activities of a single person. However there is an opportunity to utilize the sensing capabilities of wristbands to offer activity tracking services within the domain of team-based sports games. In this paper we demonstrate the design of an activity tracking system capable of detecting the players’ activities within a one-to-one basketball game. Relying on the inertial sensors of wristbands and smartphones, the system can capture the shooting attempts of each player and provide statistics about their performance. The system is based on a two- level classification architecture, combining data from both players in the game. We employ a technique for semi-automatic labelling of the ground truth that requires minimum manual input during a training game. Using a single game as a training dataset, and applying the classifier on future games we demonstrate that the system can achieve a good level of accuracy detecting the shooting attempts of both players in the game (precision 91.34%, recall 94.31%).
  • Lee, J., Efstratiou, C. and Bai, L. (2016). OSN Mood Tracking: Exploring the Use of Online Social Network Activity as an Indicator of Mood Changes. in: Workshop on Mental Health Sensing and Intervention in conjunction with UBICOMP'16. pp. 1171-1179.
    Online social networks (OSNs) have become an integral part of our everyday lives, where we share our thoughts and feelings. This study analyses the extent to which the changes of an individual’s real-world psychological mood can be inferred by tracking their online activity on Face- book and Twitter. By capturing activities from the OSNs and ground truth data via experience sampling, it was found that mood changes can be detected within a window of 7 days for 61% of the participants by using specific, combined on- line activity signals. The participants fall into three distinct groups: those whose mood correlates positively with their online activity, those who correlate negatively and those who display a weak correlation. We trained two classifiers to identify these groups using features from their online activity, which achieved precision of 95.2% and 84.4% respectively. Our results suggest that real-world mood changes can be passively tracked through online activity on OSNs.
  • Brown, C. et al. (2014). The Architecture of Innovation: Tracking Face-to-Face Interactions with UbiComp Technologies. in: ACM International Joint Conference on Pervasive and Ubiquitous Computing (UbiComp 2014).
    The layouts of the buildings we live in shape our everyday lives. In office environments, building spaces affect employees’ communication, which is crucial for productivity and innovation. However, accurate measurement of how spatial layouts affect interactions is a major challenge and traditional techniques may not give an objective view.
    We measure the impact of building spaces on social inter- actions using wearable sensing devices. We study a single organization that moved between two different buildings, affording a unique opportunity to examine how space alone can affect interactions. The analysis is based on two large scale deployments of wireless sensing technologies: short-range, lightweight RFID tags capable of detecting face-to-face interactions. We analyze the traces to study the impact of the building change on social behavior, which represents a first example of using ubiquitous sensing technology to study how the physical design of two workplaces combines with organizational structure to shape contact patterns.
  • Brown, C. et al. (2014). Tracking serendipitous interactions: how individual cultures shape the office. in: 17th ACM conference on Computer supported cooperative work & social computing. New York: ACM, pp. 1072-1081. Available at: http://dx.doi.org/10.1145/2531602.2531641.
    In many work environments, serendipitous interactions between members of different groups may lead to enhanced productivity, collaboration and knowledge dissemination. Two factors that may have an influence on such interactions are cultural differences between individuals in highly multicultural workplaces, and the layout and physical spaces of the workplace itself. In this work, we investigate how these two factors may facilitate or hinder inter-group interactions in the workplace. We analyze traces collected using wearable electronic badges to capture face-to-face interactions and mobility patterns of employees in a research laboratory in the UK. We observe that those who interact with people of different roles tend to come from collectivist cultures that value relationships and where people tend to be comfortable with social hierarchies, and that some locations in particular are more likely to host serendipitous interactions, knowledge that could be used by organizations to enhance communication and productivity.
  • Rachuri, K. et al. (2013). METIS: Exploring mobile phone sensing offloading for efficiently supporting social sensing applications. in: Proceedings of the IEEE International Conference on Pervasive Computing and Communications (PERCOM 2013).
  • Nawaz, S., Efstratiou, C. and Mascolo, C. (2013). ParkSense: A Smartphone Based Sensing System For On-Street Parking. in: Proceedings of the 19th ACM International Conference on Mobile Computing and Networking (MOBICOM 2013).
    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 ParkSense, a smartphone based sensing system that detects if a driver has vacated a parking spot. ParkSense leverages the ubiquitous Wi-Fi beacons in urban areas for sensing unparking events. It utilizes a robust Wi-Fi signature matching approach to detect driver’s return to the parked vehicle. Moreover, it uses a novel approach based on the rate of change of Wi-Fi beacons to sense if the user has started driving. We show that the rate of change of the observed beacons is highly correlated with actual user speed and is a good indicator of whether a user is in a vehicle. Through empirical evaluation, we demonstrate that our approach has a significantly smaller energy footprint than traditional location sensors like GPS and Wi-Fi based positioning while still maintaining sufficient accuracy.
  • Leontiadis, I. et al. (2012). SenShare: Transforming Sensor Networks into Multi-application Sensing Infrastructures. in: Proceedings of the 9th European Conference on Wireless Sensor Networks (EWSN 2012). Springer Berlin Heidelberg, pp. 65-81. Available at: http://dx.doi.org/10.1007/978-3-642-28169-3_5.
    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 be shared amongst multiple applications. This model however introduces many challenges, mainly related to the management of the communication of the same application running on different network nodes, and the isolation of applications within the network. In this work we present SenShare, a platform that attempts to address the technical challenges in transforming sensor networks into open access infrastructures capable of supporting multiple co-running applications. SenShare provides a clear decoupling between the infrastructure and the running application, building on the concept of overlay networks. Each application operates in an isolated environment consisting of an in-node hardware abstraction layer, and a dedicated overlay sensor network. We further report on the deployment of SenShare within our building, which presently supports the operation of multiple sensing applications, including office occupancy monitoring and environmental monitoring.
  • Nawaz, S. et al. (2012). Social sensing in the field: challenges in detecting social interactions in construction sites. in: MCSS '12 1st ACM workshop on Mobile systems for computational social science. New York: ACM, pp. 28-32. Available at: http://dx.doi.org/10.1145/2307863.2307872.
    Construction industry is a sector that is renowned for the slow uptake of new technologies. This is usually due to the conservative nature of this sector that relies heavily on tried and tested and successful old business practices. However, there is an eagerness in this industry to adopt Building Information Modelling (BIM) technologies to capture and record accurate information about a building project. But vast amounts of information and knowledge about the construction process is typically hidden within informal social interactions that take place in the work environment. In this paper we present a vision where smartphones and tablet devices carried by construction workers are used to capture the interaction and communication between workers in the field. Informal chats about decisions taken in the field, impromptu formation of teams, identification of key persons for certain tasks, and tracking the flow of information across the project community, are some pieces of information that could be captured by employing social sensing in the field. This information can not only be used during the construction to improve the site processes but it can also be exploited by the end user during maintenance of the building. We highlight the challenges that need to be overcome for this mobile and social sensing system to become a reality.
  • Efstratiou, C. et al. (2012). Sense and Sensibility in a Pervasive World. in: Proceedings of 10th International Conference on Pervasive Computing (PERVASIVE 2012).
    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 fine-grained real-world sensing. However, the introduction of passive sensing into a social networking application disrupts the traditional, user-initiated input to social services, raising both privacy and acceptability concerns. In this work we present an empirical study of the introduction of a sensor-driven social sharing application within the working environment of a research institution. Our study is based on a real deployment of a system that involves location tracking, conversation monitoring, and interaction with physical objects. By utilizing surveys, interviews and experience sampling techniques, we report on our findings regarding privacy and user experience issues, and significant factors that can affect acceptability of such services by the users. Our results suggest that such systems deliver significant value in the form of self reflection and comparison with others, while privacy concerns are raised primarily by the limited control over the way individuals are projected to their peers.
  • Hossmann, T., Efstratiou, C. and Mascolo, C. (2012). Collecting big datasets of human activity one checkin at a time. in: HotPlanet '12, 4th ACM international workshop on Hot topics in planet-scale measurement. New York: ACM, pp. 15-20. Available at: http://dx.doi.org/10.1145/2307836.2307842.
    A variety of cutting edge applications for mobile phones exploit the availability of phone sensors to accurately infer the user activity and location to offer more effective services. To validate and evaluate these new applications, appropriate and extensive datasets are needed: in particular, large sets of traces of sensor data (accelerometer, GPS, micro- phone, etc.), labelled with corresponding user activities. So far, such traces have only been collected in short-lived, small-scale setups. The primary reason for this is the difficulty in establishing accurate ground truth information outside the laboratory. Here, we present our vision of a system for large-scale sensor data capturing, leveraging all sensors of todays smart phones, with the aim of generating a large dataset that is augmented with appropriate ground-truth information. The primary challenges that we address consider the energy cost on the mobile device and the incentives for users to keep running the system on their device for longer. We argue for leveraging the concept of the checkin - as successfully introduced in online social networks (e.g. Foursquare) - for collecting activity and context related datasets. With a checkin, a user deliberately provides a small piece of data about their behaviour while enabling the system to adjust sensing and data collection around important activities.

    In this work we present up2, a mobile app letting users check in to their current activity (e.g., "waiting for the bus", "riding a bicycle", "having dinner"). After a checkin, we use the phone's sensors (GPS, accelerometer, microphone, etc.) to gather data about the user's activity and surrounding. This makes up2 a valuable tool for research in sensor based activity detection.
  • Leontiadis, I. et al. (2012). Don't kill my ads! balancing privacy in an ad-supported mobile application market. in: Twelfth Workshop on Mobile Computing Systems & Applications. New York: ACM, pp. 1-6. Available at: http://dx.doi.org/10.1145/2162081.2162084.
    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 the user's location, contacts and messages. While some mechanisms to prevent leaks of user privacy to applications have been proposed by the research community, these solutions fail to consider that application markets are primarily driven by advertisements that rely on accurately profiling the user. In this paper we take into account that there are two parties with conflicting interests: the user, interested in maintaining their privacy and the developer who would like to maximize their advertisement revenue through user profiling. We have conducted an extensive analysis of more than 250,000 applications in the Android market. Our results indicate that the current privacy protection mechanisms are not effective as developers and advert companies are not deterred. Therefore, we designed and implemented a market-aware privacy protection framework that aims to achieve an equilibrium between the developer's revenue and the user's privacy. The proposed framework is based on the establishment of a feedback control loop that adjusts the level of privacy protection on mobile phones, in response to advertisement generated revenue.
  • Clinch, S. et al. (2011). Reflections on the long-term use of an experimental digital signage system. in: 13th ACM International Conference on Ubiquitous Computing (UBICOMP 2011). ACM New York, pp. 133-142. Available at: http://dx.doi.org/10.1145/2030112.2030132.
    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 and relative ordering. Our experiences suggest that such complex feature-sets are unnecessary in many cases and may be counter productive in signage systems. We describe an alternative, simpler paradigm for encouraging widespread use of signage systems based on shared 'content channels' between content providers and display owners. Our system has been in continuous use for approximately 3 years. We reflect and draw lessons from how our user community has adopted and used the resulting public display network. We believe that these reflections will be of benefit to future developers of ubiquitous display networks.
  • Vallina-Rodriguez, N. et al. (2011). Enabling opportunistic resources sharing on mobile operating systems: benefits and challenges. in: 3rd ACM workshop on Wireless of the students, by the students, for the students. New York: ACM, pp. 29-32. Available at: http://dx.doi.org/10.1145/2030686.2030696.
    The intense use of hardware resources by mobile applications has a significant impact on the battery life of mobile devices. In this paper we introduce a novel approach for the efficient use of mobile phone resources, by considering the coordinated sharing of resources offered by multiple co-located devices. Taking into account the social behaviour of users, there are frequent situations where similar resources are available by co-located mobile phones. In this work we discuss the feasibility of sharing such resources in an opportunistic way, the possible benefits and the research challenges that need to be addressed in order to implement a reliable and robust solution.
  • Efstratiou, C. et al. (2010). A shared sensor network infrastructure. in: SenSys '10, 8th ACM Conference on Embedded Networked Sensor Systems. New York: ACM, pp. 367-368. Available at: http://dx.doi.org/10.1145/1869983.1870026.
    An increasing number of sensor networks have been deployed to monitor a variety of conditions and situations. At the same time, more and more applications are starting to rely on the data from sensor networks to provide users with (near) real-time information and conditions. This increasing demand of users for accurate information about natural and surrounding phoenomena is creating a business case for application providers.
  • Efstratiou, C. (2010). Challenges in Supporting Federation of Sensor Networks. in: NSF/FIRE Workshop on Federating Computing Resources. NSF. Available at: http://svn.planet-lab.org/wiki/FederationWorkshop.
    Wireless sensor networks are more and more seen as a solution to large-scale tracking and monitoring applications. However, existing networks are designed to serve a single application and deliver information to one authority; typically the owner of the network. This approach is clearly inefficient considering the high cost of deploying a sensor network. Supporting federation of sensor networks can allow the development of new applications that can access recourses offered by multiple existing sensor networks. This paper discusses the challenges in designing a platform for federated sensor networks.
  • Kriegel, J. et al. (2009). Smart Design for Human Performance in the Office of the Future – Requirements towards Services and Technical Advises for Tomorrows Office Work. in: AmI 2008 Workshops. Springer Berlin Heidelberg, pp. 1-5. Available at: http://dx.doi.org/10.1007/978-3-642-10607-1_1.
    The office of the future is a synonym of today’s needs and expectations towards prospective solutions and services which can support human performance in the future office work. The development of such future services is on one hand affected by the technical possibilities and on the other by the demands of changing and global work environment. The process of generating successful services can be initiated by creative methods. The 635 method is a creative brain writing technique, which follows the problem solving circle to create new uncommon ideas in a group of expert or user participants. The workshop on smart design for human performance in the office of the future used the 635 method to identify requirements towards services and technical advises for tomorrows office work. The outcome of the written brainstorming is a list of different criteria and examples which describe the several dimensions of needs and demands towards the office of the future.
  • Fitton, D. et al. (2008). Exploring the Design of Pay-Per-Use Objects in the Construction Domain. in: Proceedings of the Third European Conference on Smart Sensing and Context (EuroSSC 2008). Springer-Verlag Berlin, Heidelberg ©2008, pp. 192-205. Available at: http://dx.doi.org/10.1007/978-3-540-88793-5_15.
    Equipment used in the construction domain is often hired in order to reduce cost and maintenance overhead. The cost of hire is dependent on the time period involved and does not take into account the actual use equipment has received. This paper presents our initial investigation into how physical objects augmented with sensing and communication technologies can measure use in order to enable new pay-per-use payment models for equipment hire. We also explore user interaction with pay-per-use objects via mobile devices. The user interactions that take place within our prototype scenario range from simple information access to transactions involving multiple users. This paper presents the design, implementation and evaluation of a prototype pay-per-use system motivated by a real world equipment hire scenario. We also provide insights into the various challenges introduced by supporting a pay-per-use model, including data storage and data security in addition to user interaction issues.
  • Brown, J. et al. (2007). Network interrupts: supporting delay sensitive applications in low power wireless control networks. in: CHANTS '07 The second ACM workshop on Challenged networks. New York: ACM, pp. 51-58. Available at: http://dx.doi.org/10.1145/1287791.1287802.
    The importance in maintaining energy efficient communications in low power networks such as sensor and actuator networks is well understood. However, in recent years, a growing number of delay sensitive and interactive applications have been discovered for such networks, that are no longer purely limited to the data gathering model of sensor networks. Providing support application requiring low latency interaction in such environments without negatively affecting energy efficiency remains a challenging problem. This paper outlines the importance of this emerging class of application, discusses problems involved in supporting them in energy challenged environments, proposes a combined hardware and software mechanism based on heterogeneous wireless networking which works toward solving this problem, and goes on to evaluate this mechanism through experimental analysis. The paper concludes with a discussion of the applicability of the mechanism to typical application scenarios.
  • Davies, N. et al. (2007). Sensing Danger - Challenges in Supporting Health and Safety Compliance in the Field. in: Eighth IEEE Workshop on Mobile Computing Systems and Applications, 2007. HotMobile 2007. pp. 34-38. Available at: http://dx.doi.org/10.1109/HotMobile.2007.7.
    Many workers operate in environments that are inherently hazardous and that are subject to strict health and safety rules and regulations. We envisage a world in which physical work artefacts such as tools, are augmented with intelligent mobile nodes that are able to observe the working activities taking place, evaluate compliance with health and safety regulations and assist or actively enforce compliance with these regulations. This vision creates a new field of work in the area of health and safety aware intelligent mobile sensor networks. In this paper we describe a number of new challenges faced when developing mobile systems for compliance with health and safety regulations.
  • Efstratiou, C. et al. (2007). Experiences of Designing and Deploying Intellignent Sensor Nodes to Monitor Hand-Arm Vibrations in the Field. in: ACM MobiSys 2007. New York, USA: ACM Press, pp. 127-138.
    The NEMO project is exploring the use of mobile sensor nodes to augment physical work artefacts in order to ensure compliance with health and safety regulations. In this paper we present our experiences of designing and deploying the NEMO Hand Arm Vibration (HAV) monitoring system. Long term exposure to hand arm vibration can lead to serious health conditions and the NEMO HAV monitoring system offers an integrated architecture for capturing HAV exposure data in the field, providing feedback about exposure levels both in the field and as input to a back-end database. Our design allows health and safety regulations specified at the enterprise level to be embedded within the wireless sensor nodes allowing them to operate without any infrastructural support. The system has been the subject of a two week field trial that took place with the collaboration of a British construction and maintenance company. During the field trial, the NEMO HAV system was deployed to a road maintenance patching gang and data was collected on HAV exposure caused by hydraulic drills. The paper reports on the results of the field trial and the lessons learned through the real deployment of the system.
  • Kortuem, G. et al. (2007). Sensor Networks or Smart Artifacts? An Exploration of Organizational Issues of an Industrial Health and Safety Monitoring System. in: International Conference on Ubiquitous Computing (UbiComp 2007). Springer Berlin Heidelberg, pp. 465-482. Available at: http://dx.doi.org/10.1007/978-3-540-74853-3_27.
    Industrial health and safety is an important yet largely unexplored application area of ubiquitous computing. In this paper we investigate the relationship between technology and organization in the context of a concrete industrial health and safety system. The system is designed to reduce the number of incidents of “vibration white finger” (VWF) at construction sites and uses wireless sensor nodes for monitoring workers’ exposure to vibrations and testing of compliance with legal health and safety regulations. In particular we investigate the impact of this ubiquitous technology on the relationship between management and operatives, the formulation of health and safety rules and the risk perception and risk behavior of operatives. In addition, we contrast sensor-network inspired and smart artifact inspired compliance systems, and make the case that these technology models have a strong influence on the linkage between technology and organization.
  • Davies, N. et al. (2006). Health and Safety Compliance in the Field. in: MobiSys2006, 4th international conference on mobile systems, applications and services. New York: ACM Press. Available at: http://dl.acm.org/citation.cfm?id=1134680.
  • Efstratiou, C. et al. (2002). Utilising the event calculus for policy driven adaptation on mobile systems. in: Third International Workshop on Policies for Distributed Systems and Networks. pp. 13-24. Available at: http://dx.doi.org/10.1109/POLICY.2002.1011289.
    Adaptation is an important requirement for mobile applications due to the varying levels of resource availability that characterises mobile environments. However, without proper control, multiple applications can each adapt independently in response to a range of different adaptive stimuli, causing conflicts or suboptimal performance. In this paper, we present a policy-driven approach for mobile adaptive systems that can overcome the aforementioned problems. Our system is based on a policy language derived from the event calculus logic programming formalism. Important characteristics of our policy language are its support for explicit time-dependency expressions and its simple and user-friendly syntax
  • Efstratiou, C. et al. (2002). A platform supporting coordinated adaptation in mobile systems. in: Proceedings Fourth IEEE Workshop on Mobile Computing Systems and Applications, 2002. pp. 128-137. Available at: http://dx.doi.org/10.1109/MCSA.2002.1017492.
    Mobile environments are highly dynamic, characterised by frequent and sudden changes in resource availability. As a consequence, adaptive mobile applications need to be capable of adapting their behaviour to ensure they continue to offer the best possible level of service to the user. Our experience of developing such applications has led us to believe that existing mobile middleware platforms fail to consider adaptive applications on a host as an ensemble of entities competing for the same resources; instead, focusing on the requirements of each application in isolation. A new approach is required which offers the mechanisms to support coordination of the adaptive behaviour of multiple applications in order to achieve a common goal. We present a platform designed to meet this objective. Our platform is based on the notion of the definition of system-wide flexible adaptation policies written using a form of Kowalsky's (1992) event calculus, that may be adapted according to user needs. Moreover, we also believe that by using our approach it will soon be possible to identify and resolve conflicts caused by the need to adapt to multiple contextual triggers.
  • Blair, L. et al. (2001). `Feature' Interactions outside a Telecom Domain. in: Workshop on Feature Interactions in Composed Systems, ECOOP2001. Deventer, The Netherlands: Kluwer, B.V., pp. 233-248.
    Feature interactions in the original sense of the term (i.e. within a telecommunications domain), have now been the subject of significant research activity for over ten years. This paper considers several different sources of interactions in other domains, arising during the course of our research at Lancaster. These interactions are taken from a variety of areas within the field of Distributed Systems, and stand to benefit greatly from the application of techniques developed in the feature interaction community. Furthermore, we believe they represent a potentially important generalisation for feature interaction research.
  • Davies, N. et al. (2001). The Rational for Infrastructure Support for Adaptive and Context-Aware Applications: A Position Paper. in: NSF Workshop on Infrastructure for Mobile and Wireless Systems. Springer, pp. 146-152.
    Research has demonstrated that mobile and wireless applications benefit from a knowledge of their operating environment. Examples of contextaware or adaptive applications have been constructed and evaluated with the results being widely disseminated within the research community. However, the field is still sufficiently new that there are currently no standards for describing, disseminating or managing the necessary contextual information. Moreover, there are no standards (or even accepted best practices) for coordinating adaptation across multiple applications and systems. In this position paper we argue that the lack of standards in this area will inhibit the widespread deployment of many of the compelling context-aware mobile applications currently being designed.
  • Efstratiou, C. et al. (2001). An Architecture for the Effective Support of Adaptive Context-Aware Applications. in: Mobile Data Management (MDM'01). Berlin: Springer, pp. 15-26.
    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 service to the user. Our experiences of developing and evaluating adaptive context-aware applications in mobile environments has led us to believe that existing architectures fail to provide the necessary support for such applications. In this paper, we discuss the shortcomings of existing approaches and present work on our own architecture that has been designed to meet the key requirements of context-aware adaptive applications.
  • Cheverst, K. et al. (2000). Architectural Ideas for the Support of Adaptive Context-Aware Applications. in: Proceedings of Workshop on Infrastructure for Smart Devices - How to Make Ubiquity an Actuality, HUC'00.
  • Efstratiou, C. et al. (2000). Architectural Requirements for the Effective Support of Adaptive Mobile Applications. in: Work in progress paper in Middleware2000. Middleware: Elsevier, pp. 15-26.
    Mobile applications are required to operate in environments that change. Specifically, the availability of resources and services may change significantly during typical system operation. As a consequence, mobile applications need to be capable of adapting to these changes to ensure they offer the best possible level of service to the user. Our experiences of developing adaptive applications have led us to believe that existing middleware fails to provide the necessary support for such applications. Moreover, we believe that current research in this area is also failing to address the core requirements of adaptive mobile systems. In this paper we present a set of requirements for future mobile middleware which have been derived by considering the shortcomings of existing approaches and the needs of application developers. Key among these requirements is the need to support coordinated action between application and system components and the resolution of conflicts caused by the need to adapt to multiple contextual triggers. The paper concludes with the presentation of an architectural framework within which middleware researchers can deploy solutions to the problems identified.
  • Efstratiou, C. and Cheverst, K. (2000). Reflection: A Solution For Highly Adaptive Mobile Systems. in: Workshop on Reflective Middleware.
  • Cheverst, K. et al. (2000). Developing a context-aware electronic tourist guide. in: Proceedings of the SIGCHI conference on Human Factors in Computing Systems. pp. 17-24. Available at: http://dx.doi.org/10.1145/332040.332047.
    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 fixed durations and (like most guidebooks) are constrained by the need to satisfy the interests of the majority rather than the specific interests of individuals. Following a period of requirements capture, involving experts in the field of tourism, we developed and installed a system for use by visitors to Lancaster. The system combines mobile computing technologies with a wireless infrastructure to present city visitors with information tailored to both their personal and environmental contexts. In this paper we present an evaluation of GUIDE, focusing on the quality of the visitor's experience when using the system.
  • Costaridou, L. et al. (1997). PRONET Services for Distance Learning in Mammographic Image Processing. in: XIII International Congress of the European Federation for Medical Informatics (MIE'97). Amsterdam : IOS Press, pp. 165-177.
    The potential of telematics services is investigated with respect to learning needs of medical physicists and biomedical engineers. Telematics services are integrated into a system, the PRONET, which evolves around multimedia computer based courses and distance tutoring support. In addition, information database access and special interest group support are offered. System architecture is based on a component integration approach. The services are delivered in three modes: LAN, ISDN and Internet. Mammographic image processing is selected as an example content area.
  • Costaridou, L. et al. (1996). Modelling X-Ray Imaging Procedures: A Tool for Generating Learning Tasks. in: XII International Congress of the European Federation for Medical Informatics (MIE'96). Amsterdam : IOS Press, pp. 1047-1051.


  • Efstratiou, C. (2004). Coordinated Adaptation for Adaptive Context-aware Applications.
    The ability to adapt to change is critical to both mobile and context-aware applications.
    This thesis argues that providing suf�cient support for adaptive context-aware applications
    requires support for coordinated adaptation. Speci�cally, the main argument
    of this thesis is that coordinated adaptation requires applications to delegate adaptation
    control to an entity that can receive state information from multiple applications and
    trigger adaptation in multiple applications. Furthermore, coordination requires support
    for recon�guration of the adaptive behaviour and user involvement. Failure to support
    coordinated adaptation is shown to lead to poor system and application performance and
    insuf�cient support for user requirements.
    An investigation of the existing state-of-the-art in the areas of adaptive and contextaware
    systems and an analysis of the limitations of existing systems leads to the establishment
    of a set of design requirements for the support of coordinated adaptation.
    Speci�cally, adaptation control should be decoupled from the mechanisms implementing
    the adaptive behaviour of the applications, applications should externalise both state
    information and the adaptive mechanisms they support and the adaptation control mechanism
    should allow modi�cations without the need for re-implementation of either the
    application or the support platform.
    This thesis presents the design of a platform derived from the aforementioned requirements.
    This platform utilises a policy based mechanism for controlling adaptation.
    Based on the particular requirements of adaptive context-aware applications a new policy
    language is de�ned derived from Kowalsky's Event Calculus logic programming
    formalism. This policy language allows the speci�cation of policy rules where conditions
    are de�ned through the expression of temporal relationships between events and
    entities that represent duration (i.e. �uents). A prototype implementation of this design
    allowed the evaluation of the features offered by this platform. This evaluation reveals
    that the platform can support coordinated adaptation with acceptable performance cost.
  • Efstratiou, C. (1998). A Tool for Video and Audio Synchronisation Over the Internet.


  • Raverdy, P. et al. (2009). System and method for effectively providing user information from a user device.
    A system and method for effectively providing user information from a user device includes an event server that provides restricted access to various types of event content information and services related to a particular event or user community. A wireless portable user device may provide an access code to the event server at a particular event location through a wireless base station that is coupled to a local area network. A system user may thereby utilize the user device to access the event server for downloading appropriate event content information and related community services. The user device may provide one or more different types of profiles and other user feedback to the event server to thereby enable the event server to effectively associate the user device with appropriate event content or other types of related community services.
  • Raverdy, P. et al. (2005). System and method for selectively providing information to a user device.
    A system and method for selectively providing information to a user device includes an event server that provides restricted access to various types of event content information and services related to a particular event. A wireless portable user device may provide an access code to the event server at a particular event location through a wireless base station that is coupled to a local area network. A system user may thereby utilize the user device to access the event server for downloading appropriate event content information and related services until the foregoing access code expires.
  • Raverdy, P. et al. (2005). System and method to support gaming in an electronic network.
    A system and method to support electronic gaming in an electronic network includes an event server that provides restricted access to various types of game services. One or more system users may utilize corresponding wireless portable user devices for connecting to the event server to thereby gain access to the foregoing game services as game participants. The system users may thereby utilize the user devices to access the event server for accessing appropriate gaming services and related information. In addition, a source system user may utilize a source user device to perform a transfer procedure for transferring ownership rights of an electronic certificate related to the electronic gaming to a target system user through a target user device. The foregoing transfer procedure may be conducted through the event server, or may occur directly from the source user device to the target user device.
  • Raverdy, P. et al. (2001). System and method for streaming video information to a user device.
    A system and method for streaming video information to a user device includes an event server that provides restricted access to various types of event content information and services related to a particular event. A wireless portable user device may provide an access code to the event server at a particular event location through a wireless base station that is coupled to a local area network. A system user may thereby utilize the user device to access the event server for downloading appropriate event content information and related services. The event content information may include a direct broadcast of streaming video produced by a video service provider from local video cameras positioned at the particular event. In addition, the event content information may include a plurality of event broadcasts that may be generated by the event server after receiving and storing program information from the local video cameras, the Internet, and various external program sources. The system user may also request individual video-on-demand services for downloading specific requested information from the event server.

Edited book

  • Gerhäuser, H. et al. eds. (2008). Constructing Ambient Intelligence. Springer Berlin Heidelberg.