A. Elsts, S. Duquennoy, X. Fafoutis, G. Oikonomou, R. Piechocki, I. Craddock, "Microsecond-Accuracy Time Synchronization Using the IEEE 802.15.4 TSCH Protocol", in Proc. International Workshop on Practical Issues in Building Sensor Network Applications (IEEE SenseApp 2016), 2016
Time-Slotted Channel Hopping from the IEEE 802.15.4-2015 standard requires that network nodes are tightly time-synchronized. Existing implementations of TSCH on embedded hardware are characterized by tens-of-microseconds large synchronization errors; higher synchronization accuracy would enable reduction of idle listening time on receivers, in this way decreasing the energy required to run TSCH. For some applications, it would also allow to replace dedicated time synchronization mechanisms with TSCH. We show that time synchronization errors in the existing TSCH implementations on embedded hardware are caused primarily by imprecise clock drift estimations, rather than by real unpredictable drift variance. By estimating clock drift more precisely and by applying adaptive time compensation on each node in the network, we achieve microsecond accuracy time synchronization on point-to-point links and a <2 microsecond end-to-end error in a 7-node line topology. Our solution is implemented in the Contiki operating system and tested on Texas Instruments CC2650-based nodes, equipped with common off-the-shelf hardware clock sources (20 ppm drift). Our implementation uses only standard TSCH control messages and is able to keep radio duty cycle below 1\%.
P. Woznowski, D. Kaleshi, G. Oikonomou, I. Craddock, "Classification and Suitability of Sensing Technologies for Activity Recognition", Computer Communications, 89-90, pp. 34-50, 2016
Wider availability of sensors and sensing systems has pushed research in the direction of automatic activity recognition (AR) either for medical or other personal benefits e.g. wellness or fitness monitoring. Researchers apply different AR techniques/algorithms and use a wide range of sensors to discover home activities. However, it seems that the AR algorithms are purely technology-driven rather than informing studies on the type and quality of input required. There is an expectation to over-instrument the environment or the subjects and then develop AR algorithms, where instead the problem should be approached from a different angle i.e. what sensors (type, quality and quantity) a given algorithm requires to infer particular activities with a certain confidence? This paper introduces the concept of activity recognition, its taxonomy and familiarises the reader with sub-classes of sensor-based AR. Furthermore, it presents an overview of existing health services Telecare and Telehealth solutions, and introduces the hierarchical taxonomy of human behaviour analysis tasks. This work is a result of a systematic literature review and it presents the reader with a comprehensive set of home-based activities of daily living (ADL) and sensors proven to recognise these activities. Apart from reviewing usefulness of various sensing technologies for home-based AR algorithms, it highlights the problem of technology-driven cycle of development in this area.
P. Andriotis, G. Oikonomou, T. Tryfonas, S. Li, "Highlighting Relationships of a Smartphone’s Social Ecosystem in Potentially Large Investigations", IEEE Transactions on Cybernetics, IEEE, 46(9), pp. 1974-1985, 2016
Social media networks are becoming increasingly popular because they can satisfy diverse needs of individuals (both personal and professional). Modern mobile devices are empowered with increased capabilities, taking advantage of the technological progress that makes them smarter than their predecessors. Thus, a smartphone user is not only the phone owner, but also an entity that may have different facets and roles in various social media networks. We believe that these roles can be aggregated in a single social ecosystem, which can be derived by the smartphone. In this paper, we present our concept of the social ecosystem in contemporary devices and we attempt to distinguish the different communities that occur from the integration of social networking in our lives. In addition, we propose techniques to highlight major actors within the ecosystem. Moreover, we demonstrate our suggested visualization scheme, which illustrates the linking of entities that live in separate communities using data taken from the smartphone. Finally, we extend our concept to include various parallel ecosystems during potentially large investigations and we link influential entities in a vertical fashion. We particularly examine cases where data aggregation is performed by specific applications, producing volumes of textual data that can be analyzed with text mining methods. Our analysis demonstrates the risks of the rising ``bring your own device'' trend in enterprise environments.
A. Mavromatis, G. Papadopoulos, X. Fafoutis, A. Elsts, G. Oikonomou, T. Tryfonas, "Impact of Guard Time Length on IEEE 802.15.4e TSCH Energy Consumption", in Proc. IEEE International Conference on Sensing, Communication and Networking (SECON), 2016
The IEEE 802.15.4-2015 standard defines a number of Medium Access Control (MAC) layer protocols for low- power wireless communications in the IoT. Originally defined in the IEEE 802.15.4e amendment, TSCH (Time Slotted Channel Hopping) is among the proposed mechanisms. TSCH is a scheme aiming to guarantee network reliability by keeping nodes time-synchronised at the MAC layer. In order to ensure successful communication between a sender and a receiver, the latter starts listening shortly before the expected time of a MAC layer frame’s arrival. The offset between the time a node starts listening and the estimated time of frame arrival is called guard time and it aims to reduce the probability of missed frames due to clock drift. In this poster, we investigate the effect of the guard time duration on energy consumption. We identify that, when using the 6tisch minimal schedule, the most significant cause of energy consumption is idle listening during guard time. Therefore, the energy-efficiency of TSCH can be significantly improved by guard time optimisation. Our performance evaluation results, conducted using the Contiki operating system, show that an efficient configuration of guard time may reduce energy consumption by up to 30%, without compromising network reliability.
G. Papadopoulos, V. Kotsiou, A. Gallais, G. Oikonomou, P. Chatzimisios, T. Tryfonas, T. Noël, "A Mobility-Supporting MAC Scheme for Bursty Traffic in IoT and WSNs", in Proc. IEEE GLOBECOM, 2016
Recent boom of mobile applications has become an essential class of mobile Internet of Things (IoT), whereby large amounts of sensed data are collected and shared by mobile sensing devices for observing phenomena such as traffic or the environmental. However, most of the existing Medium Access Control (MAC) protocols mainly focus on static networks. Thus, mobile sensor nodes may pose many communication challenges during the design and development of a MAC protocol. These difficulties first require an efficient connection establishment between a mobile and static node, and then an effective data packet transmissions. In this study, we propose MobIQ, a MAC scheme that allows an advanced mobility-handling scheme for low-power MAC protocols, which allows for efficient neighbour(hood) discovery and low-delay communication. Our thorough performance evaluation, conducted on top of Contiki OS, shows that MobIQ outperforms state-of-the-art solutions such as MoX-MAC, MOBINET and ME-ContikiMAC, in terms of reducing both delay, contention to the medium and energy consumption.
G. Papadopoulos, A. Mavromatis, X. Fafoutis, N. Montavont, R. Piechocki, T. Tryfonas, G. Oikonomou, "Guard Time Optimisation and Adaptation for Energy Efficient Multi-hop TSCH Networks", in Proc. IEEE World Forum on Internet of Things (WF-IoT), 2016
In the IEEE 802.15.4-2015 standard, Time Slotted Channel Hopping (TSCH) aims to guarantee high-level network reliability by keeping nodes time-synchronised. In order to ensure successful communication between a sender and a receiver, the latter starts listening shortly before the expected time of a MAC layer frame’s arrival. The offset between the time a node starts listening and the estimated time of frame arrival is called guard time and it aims to reduce the probability of missed frames due to clock drift. In this paper, we investigate the impact of the guard time on network performance. We identify that, when using the 6tisch minimal schedule, the most significant cause of energy consumption is idle listening during guard time. Therefore, we first perform mathematical modelling on a TSCH link to identify the guard time that maximises the energy-efficiency of the TSCH network in single hop topology. We then continue in multi-hop network, where we empirically adapt the guard time locally at each node depending its distance, in terms of hops, from the sink. Our performance evaluation results, conducted using the Contiki OS, demonstrate that the proposed decentralised guard time adaptation can reduce the energy consumption by up to 40\%, without compromising network reliability.
G. Papadopoulos, A. Georgallides, T. Tryfonas, G. Oikonomou, "BMFA: Bi-Directional Multicast Forwarding Algorithm for RPL-based 6LoWPANs", in 2nd EAI International Conference on Interoperability in IoT, 2016
In scenarios involving point-to-multipoint network traffic, transmitting to each destination individually with unicast may lead to poor utilisation of network bandwidth, excessive energy consumption caused by the high number of packets and suffers from low scalability as the number of destinations increases. An alternative approach, would be to use network-layer multicast, where packets are transmitted to multiple destinations simultaneously. In doing so, applications adopting a one-to-many communication paradigm may improve their energy efficiency and bandwidth utilisation. In this paper, we present Bi-directional Multicast Forwarding Algorithm (BMFA), a novel RPL-based multicast forwarding mechanism. BMFA improves its pre-predecessor SMRF in that it allows multicast traffic to travel both upwards as well as downwards in an RPL tree. At the same time, it retains SMRF’s low latency and very low energy consumption characteristics. Our performance evaluation results, conducted using the Contiki operating system, show that BMFA outperforms its rival Trickle Multicast / Multicast Protocol for Low power and Lossy Networks (TM / MPL), in terms of reducing both delay and energy consumption.
G. Papadopoulos, A. Mavromatis, X. Fafoutis, R. Piechocki, T. Tryfonas, G. Oikonomou, "Guard Time Optimisation for Energy Efficiency in IEEE 802.15.4-2015 TSCH Links", in 2nd EAI International Conference on Interoperability in IoT, 2016
Time Slotted Channel Hopping (TSCH) is among the Medium Access Control (MAC) schemes defined in the IEEE 802.15.4-2015 standard. TSCH aims to guarantee high-level network reliability by keeping nodes time-synchronised. In order to ensure successful communication between a sender and a receiver, the latter starts listening shortly before the expected time of a MAC layer frame’s arrival. The offset between the time a node starts listening and the estimated time of frame arrival is called guard time and it aims to reduce the probability of missed frames due to clock drift. In this paper, we investigate the impact of the guard time length on network performance. We identify that, when using the 6TiSCH minimal schedule, the most significant cause of energy consumption is idle listening during guard time. Therefore, we perform empirical optimisations on the guard time to maximise the energy-efficiency of a TSCH link. Our experiments, conducted using the Contiki OS, show that optimal guard time configuration can reduce energy consumption by up to 40\%, without compromising network reliability.
G. Margelis, X. Fafoutis, R. Piechocki, G. Oikonomou, T. Tryfonas, P. Thomas, "Practical Limits of the Secret Key-Capacity for IoT Physical Layer Security", in Proc. IEEE World Forum on Internet of Things (WF-IoT), 2016
The confidentiality of communications in the Internet of Things (IoT) is critical, with cryptography being currently the most widely employed method to achieve it. Establishing cryptographically secure communication links between two transceivers requires the pre-agreement on some key, unknown to an external attacker. In recent years there has been growing interest for techniques that generate a shared random key through observation of the channel and its effects on the exchanged messages. The maximum length of that key is characterised by the Mutual Information (MI) between the observations of the two radios. In this work we examine the practical limits of the MI of off-the-shelf transceivers communicating through the IEEE 802.15.4 specification in an indoor office environment, and calculate the secret-key capacity, that is, the maximum length of an extracted secret-key in the presence of an eavesdropper. Furthermore, we study how using groups of observations can affect the MI and both analytically and experimentally prove that grouping observations leads to better results and an increased key-capacity.
V. Kumar, G. Oikonomou, T. Tryfonas, "Traffic Forensics for IPv6-Based Wireless Sensor Networks and the Internet of Things", in Proc. IEEE World Forum on Internet of Things (WF-IoT), 2016
Research and standardisation efforts in the fields of Wireless Sensor Networks (WSNs) and the Internet of Things (IoT) are leading towards the adoption of TCP/IP for deployments of networks of severely constrained smart embedded objects. As a result, wireless sensors can now be uniquely identified by an IPv6 address and thus be directly connected to and reachable from the internet. This has a series of advantages but also exposes sensor deployments to new security vulnerabilities. Should a deployment be compromised, post-incident analysis can provide information about the nature of the attack by inspecting the network’s state and traffic during the time period prior, during and after the attack. In this paper we adopt traffic forensic techniques in order to achieve post-hoc detection of attacks against availability in IPv6-based Low-Power Wireless Personal Area Networks. To this end, we first implement an attack which exploits inherent vulnerabilities of the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL). Subsequently, we present an automated method to detect and analyse this attack by examining network packet captures.
A. Fragkiadakis, G. Oikonomou, H. Pöhls, E. Tragos, M. Wojcik, T. Tryfonas, "Securing Communications Among Severely Constrained, Wireless Embedded Devices", in Engineering Secure IoT Systems, IET, 2016
The goal of this chapter is to present the ideas and concepts of the EU-FP7 SMARTCITIES project “RERUM” with regards to improving the communication security in IoT-based smart city applications. The chapter tries to identify the gaps in previous IoT frameworks with regards to security and privacy and shows the advances that RERUM brings to the IoT community with its significant focus on embedded device functionalities. The goal of the RERUM secure communications framework is to provide light-weight solutions so that they can be applied even in the very constrained IoT devices. Solutions for lightweight encryption (based on the relatively new theory of Compressive Sensing), on transport-layer security (based on DTLS) and on integrity verification of data (using on-device signatures) are presented in detail, discussing their applicability and the benefits they bring to IoT.
X. Fafoutis, L. Marchegiani, G. Papadopoulos, R. Piechocki, T. Tryfonas, G. Oikonomou, "Privacy Leakage of Physical Activity Levels in Wireless Embedded Wearable Systems", Signal Processing Letters, IEEE, 24(2), pp. 136-140, 2016
With the ubiquity of sensing technologies in our personal spaces, the protection of our privacy and the confidentiality of sensitive data becomes a major concern. In this paper, we focus on wearable embedded systems that communicate data periodically over the wireless medium. In this context, we demonstrate that private information about the physical activity levels of the wearer can leak to an eavesdropper through the physical layer. Indeed, we show that the physical activity levels strongly correlate with changes in the wireless channel that can be captured by measuring the signal strength of the eavesdropped frames. We practically validate this correlation in several scenarios in a real residential environment, using data collected by our prototype wearable accelerometer-based sensor. Lastly, we propose a privacy enhancement algorithm that
mitigates the leakage of this private information.
P. Andriotis, G. Oikonomou, A. Mylonas, T. Tryfonas, "A Study on Usability and Security Features of the Android Pattern Lock Screen", Information and Computer Security, Emerald, 24(1), pp. 53-72, 2016
The Android pattern lock screen (or graphical password) is a popular user authentication method that relies on the advantages provided by the visual representation of a password, which enhance its memorability. Graphical passwords are vulnerable to attacks (e.g. shoulder surfing); thus, the need for more complex passwords becomes apparent. This paper aims to focus on the features that constitute a usable and secure pattern and investigate the existence of heuristic and physical rules that possibly dictate the formation of a pattern.
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