2018
[19]
A. Elsts, X. Fafoutis, S. Duquennoy, G. Oikonomou, R. Piechocki, I. Craddock, "Temperature-Resilient Time Synchronization for the Internet of Things", IEEE Transactions on Industrial Informatics, IEEE, 14(5), pp. 2241-2250, 2018
@article{Elsts-2018-tii, title = {Temperature-Resilient Time Synchronization for the Internet of Things}, author = {Atis Elsts and Xenofon Fafoutis and Simon Duquennoy and George Oikonomou and Robert Piechocki and Ian Craddock}, journal = {IEEE Transactions on Industrial Informatics}, publisher = {IEEE}, doi = {10.1109/TII.2017.2778746}, pages = {2241-2250}, volume = {14}, number = {5}, year = {2018}, month = {May}, oa-url = {https://research-information.bristol.ac.uk/en/publications/temperatureresilient-time-synchronization-for-the-internet-of-things(429dd808-1364-40e3-9c88-085f68ab37c9).html}, gsid = {999822098705616907}, abstract = {Networks deployed in real-world conditions have to cope with dynamic, unpredictable environmental temperature changes. These changes affect the clock rate on network nodes, and can cause faster clock de-synchronization compared to situations where devices are operating under stable temperature conditions. Wireless network protocols such as Time-Slotted Channel Hopping (TSCH) from the IEEE 802.15.4-2015 standard are affected by this problem, since they require tight clock synchronization among all nodes for the network to remain operational. This paper proposes a method for autonomously compensating temperature-dependent clock rate changes. After a calibration stage, nodes continuously perform temperature measurements to compensate for clock drifts at run-time. The method is implemented on low-power IoT nodes and evaluated through experiments in a temperature chamber, indoor and outdoor environments, as well as with numerical simulations. The results show that applying the method reduces the maximum synchronization error more than 10 times. In this way, the method allows reduce the total energy spent for time synchronization, which is practically relevant concern for low data rate, low energy budget TSCH networks, especially those exposed to environments with changing temperature.} }
Networks deployed in real-world conditions have to cope with dynamic, unpredictable environmental temperature changes. These changes affect the clock rate on network nodes, and can cause faster clock de-synchronization compared to situations where devices are operating under stable temperature conditions. Wireless network protocols such as Time-Slotted Channel Hopping (TSCH) from the IEEE 802.15.4-2015 standard are affected by this problem, since they require tight clock synchronization among all nodes for the network to remain operational. This paper proposes a method for autonomously compensating temperature-dependent clock rate changes. After a calibration stage, nodes continuously perform temperature measurements to compensate for clock drifts at run-time. The method is implemented on low-power IoT nodes and evaluated through experiments in a temperature chamber, indoor and outdoor environments, as well as with numerical simulations. The results show that applying the method reduces the maximum synchronization error more than 10 times. In this way, the method allows reduce the total energy spent for time synchronization, which is practically relevant concern for low data rate, low energy budget TSCH networks, especially those exposed to environments with changing temperature.
[18]
X. Fafoutis, A. Elsts, G. Oikonomou, R. Piechocki, I. Craddock, "Adaptive Static Scheduling in IEEE 802.15.4 TSCH Networks", in Proc. IEEE WF-IoT, pp. 263-268, 2018
@INPROCEEDINGS{Fafoutis-2018-wfiot, author = {Xenofon Fafoutis and Atis Elsts and George Oikonomou and Robert Piechocki and Ian Craddock}, title = {Adaptive Static Scheduling in IEEE 802.15.4 TSCH Networks}, publisher = {IEEE}, booktitle = {Proc. IEEE WF-IoT}, month = feb, pages = {263-268}, year = {2018}, doi = {10.1109/WF-IoT.2018.8355114}, gsid = {12784464564427922876}, oa-url = {https://research-information.bristol.ac.uk/en/publications/adaptive-static-scheduling-in-ieee-802154-tsch-networks(bfafab3a-7f19-4ac6-80b3-b2090ce85a90).html}, abstract = {TSCH (Time-Slotted Channel Hopping) is a synchronous MAC (Medium Access Control) protocol, introduced with the recent amendments to the IEEE 802.15.4 standard. Due to its channel hopping nature, TSCH is a promising enabling technology for dependable IoT (Internet of Things) infrastructures that are deployed in environments that are prone to interference. In TSCH, medium access is orchestrated by a schedule that is distributed to all the nodes in the network. In this paper, we propose Adaptive Static Scheduling to improve the energy efficiency of TSCH networks. Adaptive Static Scheduling builds on top of static schedules and allows each pair of communicating nodes to adaptively activate a subset of their allocated slots, effectively reducing the idle listening overhead of unused slots. Moreover, the nodes can dynamically activate more slots when they need to support bursts of high traffic, without the need of redistributing new schedules. Simulation results demonstrate that Adaptive Static Scheduling outperforms static scheduling in dynamic environments, operating nearly as efficiently as an oracle with knowledge of the optimal schedule.}, }
TSCH (Time-Slotted Channel Hopping) is a synchronous MAC (Medium Access Control) protocol, introduced with the recent amendments to the IEEE 802.15.4 standard. Due to its channel hopping nature, TSCH is a promising enabling technology for dependable IoT (Internet of Things) infrastructures that are deployed in environments that are prone to interference. In TSCH, medium access is orchestrated by a schedule that is distributed to all the nodes in the network. In this paper, we propose Adaptive Static Scheduling to improve the energy efficiency of TSCH networks. Adaptive Static Scheduling builds on top of static schedules and allows each pair of communicating nodes to adaptively activate a subset of their allocated slots, effectively reducing the idle listening overhead of unused slots. Moreover, the nodes can dynamically activate more slots when they need to support bursts of high traffic, without the need of redistributing new schedules. Simulation results demonstrate that Adaptive Static Scheduling outperforms static scheduling in dynamic environments, operating nearly as efficiently as an oracle with knowledge of the optimal schedule.
[17]
@inproceedings{Fafoutis-2018-RealWSN, title = {On Predicting the Battery Lifetime of IoT Devices: Experiences from the SPHERE Deployments}, author = {Xenofon Fafoutis and Atis Elsts and Antonis Vafeas and George Oikonomou and Robert Piechocki}, year = {2018}, month = {11}, day = {4}, doi = {10.1145/3277883.3277892}, language = {English}, pages = {7--12}, booktitle = {Proc. RealWSN}, publisher = {Association for Computing Machinery (ACM)}, oa-url = {https://research-information.bristol.ac.uk/en/publications/on-predicting-the-battery-lifetime-of-iot-devices-experiences-from-the-sphere-deployments(05c0efb7-16c9-47fc-b0e1-7fe9dc6f21ec).html}, gsid = {10336648821840413740}, doi = {10.1145/3277883.3277892}, abstract = {One of the challenges of deploying IoT battery-powered sensing systems is managing the maintenance of batteries. To that end, practitioners often employ prediction techniques to approximate the battery lifetime of the deployed devices. Following a series of longterm residential deployments in the wild, this paper contrasts real-world battery lifetimes and discharge patterns against battery lifetime predictions that were conducted during the development of the deployed system. The comparison highlights the challenges of making battery lifetime predictions, in an attempt to motivate further research on the matter. Moreover, this paper summarises key lessons learned that could potentially accelerate future IoT deployments of similar scale and nature.}, }
One of the challenges of deploying IoT battery-powered sensing systems is managing the maintenance of batteries. To that end, practitioners often employ prediction techniques to approximate the battery lifetime of the deployed devices. Following a series of longterm residential deployments in the wild, this paper contrasts real-world battery lifetimes and discharge patterns against battery lifetime predictions that were conducted during the development of the deployed system. The comparison highlights the challenges of making battery lifetime predictions, in an attempt to motivate further research on the matter. Moreover, this paper summarises key lessons learned that could potentially accelerate future IoT deployments of similar scale and nature.
[16]
A. Vafeas, A. Elsts, J. Pope, X. Fafoutis, G. Oikonomou, R. Piechocki, I. Craddock, "Energy-Efficient, Noninvasive Water Flow Sensor", in Proc. SMARTCOMP, pp. 139-146, 2018
@INPROCEEDINGS{Vafeas-2018-smartcomp, title = {Energy-Efficient, Noninvasive Water Flow Sensor}, author = {Antonis Vafeas and Atis Elsts and James Pope and Xenofon Fafoutis and George Oikonomou and Robert Piechocki and Ian Craddock}, booktitle = {Proc. SMARTCOMP}, year = {2018}, pages = {139-146}, doi = {10.1109/SMARTCOMP.2018.00084}, gsid = {1340752008608334172}, abstract = {We are interested in hot and cold water flow detection in domestic kitchen and bathroom taps for smart home environments. Water flow monitoring is particularly valuable for long-term behavioural monitoring systems for health-related applications, as it enables the collection of long-term data on the hydration levels of the house residents, and it is associated with several activities of daily life, such as cooking and cleaning. This paper presents a water flow sensing device that is based on sensing the vibrations on the pipe when water is flowing through them. The proposed solution is noninvasive and energyefficient, as it does not require cutting the water pipes or altering the plumbing system, and consumes less then 2 µA in continuous operation. The proposed water flow sensor has been integrated to SPHERE, a sensing platform of non-medical sensors for healthcare monitoring and behavioural analytics in a home environment, and deployed to more than 15 residential properties.}, }
We are interested in hot and cold water flow detection in domestic kitchen and bathroom taps for smart home environments. Water flow monitoring is particularly valuable for long-term behavioural monitoring systems for health-related applications, as it enables the collection of long-term data on the hydration levels of the house residents, and it is associated with several activities of daily life, such as cooking and cleaning. This paper presents a water flow sensing device that is based on sensing the vibrations on the pipe when water is flowing through them. The proposed solution is noninvasive and energyefficient, as it does not require cutting the water pipes or altering the plumbing system, and consumes less then 2 µA in continuous operation. The proposed water flow sensor has been integrated to SPHERE, a sensing platform of non-medical sensors for healthcare monitoring and behavioural analytics in a home environment, and deployed to more than 15 residential properties.
[15]
J. Pope, A. Vafeas, A. Elsts, G. Oikonomou, R. Piechocki, I. Craddock, "An Accelerometer Lossless Compression Algorithm and Energy Analysis for IoT Devices", in Proc. WCNC Workshops, pp. 396-401, 2018
@INPROCEEDINGS{Pope-2018-wcnc, title = {An Accelerometer Lossless Compression Algorithm and Energy Analysis for IoT Devices}, author = {James Pope and Antonis Vafeas and Atis Elsts and George Oikonomou and Robert Piechocki and Ian Craddock}, year = {2018}, booktitle = {Proc. WCNC Workshops}, publisher = {IEEE}, pages = {396-401}, doi = {10.1109/WCNCW.2018.8368985}, gsid = {4137926603080687766}, oa-url = {https://research-information.bristol.ac.uk/en/publications/an-accelerometer-lossless-compression-algorithm-and-energy-analysis-for-iot-devices(ba9c4c1b-a085-429d-a5db-d8010736b6fc).html}, abstract = {The Internet of Things promises to enable numerous future applications spanning many domains, including health care, and is comprised of devices that are constrained in terms of computational and energy resources. A specific health care application is to ascertain patients' activity of daily living while at home using accelerometer data from non-invasive wearables. It is often necessary to store this data on the device to be retrieved later for analysis. However, the devices typically store far more data than can be transmitted with commonly used low power radios. To mitigate the problem, this paper proposes an energy efficient, lossless compression algorithm that uses an offline frequency distribution to create a symbol-code lookup table. Using an extensive set of data from a previous study, an analysis of the entropy of activities of daily living accelerometer data is presented. The compression algorithm is compared against this estimated entropy. Energy being critical for IoT devices, the trade-off between energy cost for compression versus energy saved during transmission is also analysed.}, }
The Internet of Things promises to enable numerous future applications spanning many domains, including health care, and is comprised of devices that are constrained in terms of computational and energy resources. A specific health care application is to ascertain patients' activity of daily living while at home using accelerometer data from non-invasive wearables. It is often necessary to store this data on the device to be retrieved later for analysis. However, the devices typically store far more data than can be transmitted with commonly used low power radios. To mitigate the problem, this paper proposes an energy efficient, lossless compression algorithm that uses an offline frequency distribution to create a symbol-code lookup table. Using an extensive set of data from a previous study, an analysis of the entropy of activities of daily living accelerometer data is presented. The compression algorithm is compared against this estimated entropy. Energy being critical for IoT devices, the trade-off between energy cost for compression versus energy saved during transmission is also analysed.
[14]
G. Margelis, X. Fafoutis, G. Oikonomou, R. Piechocki, T. Tryfonas, P. Thomas, "Efficient DCT-based Secret Key Generation for the Internet of Things", Ad Hoc Networks, Elsevier, 2018
@article{Margelis-2018-AdHoc, author = {George Margelis and Xenofon Fafoutis and George Oikonomou and Robert Piechocki and Theo Tryfonas and Paul Thomas}, title = {Efficient DCT-based Secret Key Generation for the Internet of Things}, journal = {Ad Hoc Networks}, publisher = {Elsevier}, year = {2018}, gsid = {5818991158831943032}, doi = {10.1016/j.adhoc.2018.08.014}, oa-url = {https://www.sciencedirect.com/science/article/pii/S1570870518305948}, abstract = {Internet of Things (IoT) Security is critical, and the most widely employed method to ensure robust confidentiality is cryptography. However, 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 in techniques that generate a shared random key through observation of the channel and its effects on the exchanged messages. In this work we present SKYGlow, a novel scheme for secret-key generation, designed for low-power IoT devices and tested on IEEE 802.15.4 transceivers. We first examine the practical upper bounds of the maximum length of the secret-key that can be generated by communicating IEEE 802.15.4 devices. We contrast that upper-bound with the current state-of-the-art, and elaborate on the workings of our proposed scheme. SKYGlow applies the Discreet Cosine Transform (DCT) on the Received Signal Strength (RSS) values of exchanged messages to reduce mismatches and increase correlation between the generated secret-bits. We validate the performance of our scheme on both outdoor and indoor scenarios, on the 2.4 GHz and 868 MHz ISM bands. Our experiments have resulted in the creation of 128 bit secret keys with only 65 packet exchanges and with an entropy of 0.9978 bits, making our scheme much more energy efficient compared with others in the existing literature. }, }
Internet of Things (IoT) Security is critical, and the most widely employed method to ensure robust confidentiality is cryptography. However, 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 in techniques that generate a shared random key through observation of the channel and its effects on the exchanged messages. In this work we present SKYGlow, a novel scheme for secret-key generation, designed for low-power IoT devices and tested on IEEE 802.15.4 transceivers. We first examine the practical upper bounds of the maximum length of the secret-key that can be generated by communicating IEEE 802.15.4 devices. We contrast that upper-bound with the current state-of-the-art, and elaborate on the workings of our proposed scheme. SKYGlow applies the Discreet Cosine Transform (DCT) on the Received Signal Strength (RSS) values of exchanged messages to reduce mismatches and increase correlation between the generated secret-bits. We validate the performance of our scheme on both outdoor and indoor scenarios, on the 2.4 GHz and 868 MHz ISM bands. Our experiments have resulted in the creation of 128 bit secret keys with only 65 packet exchanges and with an entropy of 0.9978 bits, making our scheme much more energy efficient compared with others in the existing literature.
[13]
X. Fafoutis, A. Elsts, G. Oikonomou, R. Piechocki, "SPHERE Deployment Manager: A Tool for Deploying IoT Sensor Networks at Large Scale", in Proc. AdHoc Now, ser. LNCS, 11104, pp. 307-318, 2018
@inproceedings{Fafoutis-2018-AdHocNow, title={SPHERE Deployment Manager: A Tool for Deploying IoT Sensor Networks at Large Scale}, author={Fafoutis, Xenofon and Elsts, Atis and Oikonomou, George and Piechocki, Robert}, booktitle={Proc. AdHoc Now}, pages={307--318}, year={2018}, gsid = {6516981089610036943}, doi = {10.1007/978-3-030-00247-3_27}, volume = {11104}, publisher = {Springer}, oa-url = {https://research-information.bristol.ac.uk/en/publications/sphere-deployment-manager(81e729f8-7f20-49af-b76c-43ad9dbe09e0).html}, series = {LNCS}, abstract = {Internet of Things (IoT) technology has the potential to revolutionise several domains of everyday life, including the healthcare sector. In order to reach its full potential, IoT technology needs to be evaluated in the real world, beyond controlled environments, such as laboratories and test-beds. SPHERE is an experimental sensing platform for healthcare in a residential environment. Unlike other similar smart home health systems, SPHERE is deployed in a large number of properties of volunteers. Based on our experiences and lessons learned from SPHERE’s large-scale deployments, this paper focuses on the challenge of effectively managing the sensor installation overhead, aiming at supporting our deployment technicians with achieving a satisfactory deployment throughput. In this context, this paper presents the SPHERE Deployment Manager: an open-source tool that facilitates the deployment of bespoke IoT networks by technicians that are not experts in IoT technology. We believe that the SPHERE Deployment Manager is a tool that can accelerate future IoT research deployments of similar nature and scale.}, }
Internet of Things (IoT) technology has the potential to revolutionise several domains of everyday life, including the healthcare sector. In order to reach its full potential, IoT technology needs to be evaluated in the real world, beyond controlled environments, such as laboratories and test-beds. SPHERE is an experimental sensing platform for healthcare in a residential environment. Unlike other similar smart home health systems, SPHERE is deployed in a large number of properties of volunteers. Based on our experiences and lessons learned from SPHERE’s large-scale deployments, this paper focuses on the challenge of effectively managing the sensor installation overhead, aiming at supporting our deployment technicians with achieving a satisfactory deployment throughput. In this context, this paper presents the SPHERE Deployment Manager: an open-source tool that facilitates the deployment of bespoke IoT networks by technicians that are not experts in IoT technology. We believe that the SPHERE Deployment Manager is a tool that can accelerate future IoT research deployments of similar nature and scale.
2017
[12]
@INPROCEEDINGS{Elsts-2017-dcoss, title = {Scheduling high-rate unpredictable traffic in IEEE 802.15.4 TSCH networks}, keywords = {Time slotted channel hopping, scheduling, Internet of Things}, author = {Atis Elsts and Xenofon Fafoutis and James Pope and George Oikonomou and Robert Piechocki and Ian Craddock}, year = {2017}, month = {3}, booktitle = {Proc. IEEE DCOSS}, gsid = {11148583356626153925}, publisher = {IEEE}, pages = {3-10}, doi = {10.1109/DCOSS.2017.20}, oa-url = {https://research-information.bristol.ac.uk/en/publications/scheduling-highrate-unpredictable-traffic-in-ieee-802154-tsch-networks(74903df9-1c10-438c-8a05-7a4ccad936ac).html}, abstract = {The upcoming Internet of Things (IoT) applications include real-time human activity monitoring with wearable sensors. Compared to the traditional environmental sensing with low-power wireless nodes, these new applications generate a constant stream of a much higher rate. Nevertheless, the wearable devices remain battery powered and therefore restricted to low-power wireless standards such as IEEE 802.15.4 or Bluetooth Low Energy (BLE). Our work tackles the problem of building a reliable autonomous schedule for forwarding this kind of dynamic data in IEEE 802.15.4 TSCH networks. Due to the a priori unpredictability of these data source locations, the quality of the wireless links, and the routing topology of the forwarding network, it is wasteful to reserve the number of slots required for the worst-case scenario; under conditions of high expected datarate, it is downright impossible. The solution we propose is a hybrid approach where dedicated TSCH cells and shared TSCH slots coexist in the same schedule. We show that under realistic assumptions of wireless link diversity, adding shared slots to a TSCH schedule increases the overall packet delivery rate and the fairness of the system.}, }
The upcoming Internet of Things (IoT) applications include real-time human activity monitoring with wearable sensors. Compared to the traditional environmental sensing with low-power wireless nodes, these new applications generate a constant stream of a much higher rate. Nevertheless, the wearable devices remain battery powered and therefore restricted to low-power wireless standards such as IEEE 802.15.4 or Bluetooth Low Energy (BLE). Our work tackles the problem of building a reliable autonomous schedule for forwarding this kind of dynamic data in IEEE 802.15.4 TSCH networks. Due to the a priori unpredictability of these data source locations, the quality of the wireless links, and the routing topology of the forwarding network, it is wasteful to reserve the number of slots required for the worst-case scenario; under conditions of high expected datarate, it is downright impossible. The solution we propose is a hybrid approach where dedicated TSCH cells and shared TSCH slots coexist in the same schedule. We show that under realistic assumptions of wireless link diversity, adding shared slots to a TSCH schedule increases the overall packet delivery rate and the fairness of the system.
[11]
@INPROCEEDINGS{Elsts-2017-SenseApp, title = {Microsecond-accuracy time synchronization using the IEEE 802.15.4 TSCH Protocol}, author = {Atis Elsts and Simon Duquennoy and Xenofon Fafoutis and George Oikonomou and Robert Piechocki and Ian Craddock}, year = {2017}, month = {2}, doi = {10.1109/LCN.2016.042}, oa-url = {http://research-information.bristol.ac.uk/en/publications/microsecondaccuracy-time-synchronization-using-the-ieee-802154-tsch-protocol(2e47abe7-60e9-48a7-9f09-9fe7f4859ccb).html}, booktitle = {Proc. IEEE SenseApp}, publisher = {IEEE}, gsid = {11807852472963901506}, abstract = {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%.} }
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%.
[10]
@INPROCEEDINGS{Elsts-2017-gsiot, title = {Internet of things for smart homes: lessons learned from the SPHERE case study}, author = {Atis Elsts and George Oikonomou and Xenofon Fafoutis and Robert Piechocki}, year = {2017}, month = {3}, booktitle = {Proc. GIoTS}, publisher = {IEEE}, doi = {10.1109/GIOTS.2017.8016226}, gsid = {6103776013711544890}, oa-url = {https://research-information.bristol.ac.uk/en/publications/internet-of-things-for-smart-homes(f86c4eb4-87ec-428a-8d50-9427166d97fd).html}, abstract = {Building large-scale low-power Internet of Things (IoT) systems remains a challenge, as these systems have to meet the requirements of reliability, robustness, and energy- efficiency while running on resource-restricted microcontrollers without memory protection. In this paper we present the case study of IoT in SPHERE (Sensor Platform for HEalthcare in a Residential Environment), a project with the objective to develop a multipurpose, multi-modal sensor platform for monitoring people’s health inside their homes. Atypically for academic projects, in 2017 the SPHERE software is going to be deployed in a 100-home study in volunteer homes, therefore it has to satisfy many real-world requirements. We discuss the requirements for IoT networking in this project, the IoT architecture (built on top of Contiki OS), software engineering challenges and lessons learned, as well as some of the general aspects that still make embedded low-power IoT software development difficult.}, }
Building large-scale low-power Internet of Things (IoT) systems remains a challenge, as these systems have to meet the requirements of reliability, robustness, and energy- efficiency while running on resource-restricted microcontrollers without memory protection. In this paper we present the case study of IoT in SPHERE (Sensor Platform for HEalthcare in a Residential Environment), a project with the objective to develop a multipurpose, multi-modal sensor platform for monitoring people’s health inside their homes. Atypically for academic projects, in 2017 the SPHERE software is going to be deployed in a 100-home study in volunteer homes, therefore it has to satisfy many real-world requirements. We discuss the requirements for IoT networking in this project, the IoT architecture (built on top of Contiki OS), software engineering challenges and lessons learned, as well as some of the general aspects that still make embedded low-power IoT software development difficult.
[9]
X. Fafoutis, A. Vafeas, B. Janko, S. Sherratt, J. Pope, A. Elsts, E. Mellios, G. Hilton, G. Oikonomou, R. Piechocki, I. Craddock, "Designing Wearable Sensing Platforms for Healthcare in a Residential Environment", EAI Endorsed Transactions on Pervasive Health and Technology, European Alliance for Innovation, 17(12), 2017
@article{Fafoutis-2017-eai, title = {Designing Wearable Sensing Platforms for Healthcare in a Residential Environment}, author = {Xenofon Fafoutis and Antonis Vafeas and Balazs Janko and Simon Sherratt and James Pope and Atis Elsts and Evangelos Mellios and Geoffrey Hilton and George Oikonomou and Robert Piechocki and Ian Craddock}, year = {2017}, month = {9}, doi = {10.4108/eai.7-9-2017.153063}, volume = {17}, journal = {EAI Endorsed Transactions on Pervasive Health and Technology}, issn = {2411-7145}, publisher = {European Alliance for Innovation}, number = {12}, gsid = {1445270239734662268}, oa-url = {https://research-information.bristol.ac.uk/en/publications/designing-wearable-sensing-platforms-for-healthcare-in-a-residential-environment(5a9756d4-c840-479d-a989-2e8bbaa9f0ff).html}, abstract = {Wearable technologies are valuable tools that can encourage people to monitor their own well-being and facilitate timely health interventions. In this paper, we present SPW-2; a low-profile versatile wearable sensor that employs two ultra low power accelerometers and an optional gyroscope. Designed for minimum maintenance and a long-term operation outside the laboratory, SPW-2 is able to oer a battery lifetime of multiple months. Measurements on its wireless performance in a real residential environment with thick brick walls, demonstrate that SPW-2 can fully cover a room and - in most cases - the adjacent room, as well.}, }
Wearable technologies are valuable tools that can encourage people to monitor their own well-being and facilitate timely health interventions. In this paper, we present SPW-2; a low-profile versatile wearable sensor that employs two ultra low power accelerometers and an optional gyroscope. Designed for minimum maintenance and a long-term operation outside the laboratory, SPW-2 is able to oer a battery lifetime of multiple months. Measurements on its wireless performance in a real residential environment with thick brick walls, demonstrate that SPW-2 can fully cover a room and - in most cases - the adjacent room, as well.
[8]
@INPROCEEDINGS{Margelis-2017-icc, title = {Physical layer secret-key generation with discreet cosine transform for the Internet of Things}, author = {George Margelis and Xenofon Fafoutis and George Oikonomou and Robert Piechocki and Theo Tryfonas and Paul Thomas}, year = {2017}, month = {7}, doi = {10.1109/ICC.2017.7997419}, isbn = {9781467390002}, booktitle = {Proc. IEEE ICC}, publisher = {IEEE}, gsid = {7131705677557939788}, oa-url = {https://research-information.bristol.ac.uk/en/publications/physical-layer-secretkey-generation-with-discreet-cosine-transform-for-the-internet-of-things(3d03e451-0462-4711-9bd4-c8be5232af9e).html}, abstract = {The confidentiality of communications in the Internet of Things (IoT) is critical, with cryptography currently being the most widely employed method of ensuring 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 attention in techniques that generate a shared random key through observation of the channel and its effects on the exchanged messages. In this work we present SKYGlow, a novel scheme for secret-key generation, designed for IoT devices, such as IEEE 802.15.4 and Bluetooth Low Energy (BLE) transceivers. SKYGlow employs the Discreet Cosine Transform (DCT) of channel observations and Slepian-Wolf coding for information reconciliation. Real-life experiments have resulted in the creation of 128-bit secret keys with only 65 packet exchanges and with an entropy of 0.9978 bits, making our scheme much more energy-efficient compared with others in the existing literature.}, }
The confidentiality of communications in the Internet of Things (IoT) is critical, with cryptography currently being the most widely employed method of ensuring 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 attention in techniques that generate a shared random key through observation of the channel and its effects on the exchanged messages. In this work we present SKYGlow, a novel scheme for secret-key generation, designed for IoT devices, such as IEEE 802.15.4 and Bluetooth Low Energy (BLE) transceivers. SKYGlow employs the Discreet Cosine Transform (DCT) of channel observations and Slepian-Wolf coding for information reconciliation. Real-life experiments have resulted in the creation of 128-bit secret keys with only 65 packet exchanges and with an entropy of 0.9978 bits, making our scheme much more energy-efficient compared with others in the existing literature.
[7]
P. Woznowski, A. Burrows, T. Diethe, X. Fafoutis, J. Hall, S. Hannuna, M. Camplani, N. Twomey, M. Kozlowski, B. Tan, N. Zhu, A. Elsts, A. Vafeas, A. Paiement, L. Tao, M. Mirmehdi, T. Burghardt, D. Damen, P. Flach, R. Piechocki, I. Craddock, G. Oikonomou, "SPHERE: A sensor platform for healthcare in a residential environment", in Designing, Developing, and Facilitating Smart Cities, Springer, pp. 315-333, 2017
@INCOLLECTION{Woznowski-2017-sphere, title = {SPHERE: A sensor platform for healthcare in a residential environment}, author = {Woznowski, {Przemyslaw R.} and Burrows, Alison and Diethe, Tom and Fafoutis, Xenofon and Hall, Jake and Hannuna, Sion and Camplani, Massimo and Twomey, Niall and Kozlowski, Michal and Tan, Bo and Zhu, Ni and Elsts, Atis and Vafeas, Antonis and Paiement, Adeline and Tao, Lili and Mirmehdi, Majid and Burghardt, Tilo and Damen, Dima and Flach, Peter and Piechocki, Robert and Craddock, Ian and Oikonomou, George}, editor = {Angelakis, Vangelis and Tragos, Elias and P{\"o}hls, Henrich C. and Kapovits, Adam and Bassi, Alessandro}, booktitle = {Designing, Developing, and Facilitating Smart Cities}, publisher = {Springer}, gsid = {18162269616817626173}, pages = {315--333}, isbn = {978-3-319-44924-1}, doi = {10.1007/978-3-319-44924-1_14}, year = {2017}, abstract = {It can be tempting to think about smart homes like one thinks about smart cities. On the surface, smart homes and smart cities comprise coherent systems enabled by similar sensing and interactive technologies. It can also be argued that both are broadly underpinned by shared goals of sustainable development, inclusive user engagement and improved service delivery. However, the home possesses unique characteristics that must be considered in order to develop effective smart home systems that are adopted in the real world.}, }
It can be tempting to think about smart homes like one thinks about smart cities. On the surface, smart homes and smart cities comprise coherent systems enabled by similar sensing and interactive technologies. It can also be argued that both are broadly underpinned by shared goals of sustainable development, inclusive user engagement and improved service delivery. However, the home possesses unique characteristics that must be considered in order to develop effective smart home systems that are adopted in the real world.
[6]
@INPROCEEDINGS{Fafoutis-2017-ewsn, title = {Demo: SPES-2 – A Sensing Platform for Maintenance-Free Residential Monitoring}, author = {Xenofon Fafoutis and Atis Elsts and Antonis Vafeas and George Oikonomou and Robert Piechocki}, booktitle = {Proc. EWSN 2017}, year = {2017}, gsid = {17625986834348170975}, oa-url = {http://dl.acm.org/citation.cfm?id=3108009.3108060}, abstract = {SPES-2 is a sensing board for room-level monitoring in a home environment. It constitutes a vital modality of the SPHERE architecture: a multi-modal sensing platform for healthcare in a residential environment. SPES-2 uses an optimised implementation of the IEEE 802.15.4-2015 TSCH (Time-Slotted Channel Hopping) standard to operate efficiently and reliably in unknown environments for more than one year without battery replacement, providing continuous information about the ambient characteristics of the room (such as temperature, humidity and light levels), as well as presence information captured through a motion sensor.} }
SPES-2 is a sensing board for room-level monitoring in a home environment. It constitutes a vital modality of the SPHERE architecture: a multi-modal sensing platform for healthcare in a residential environment. SPES-2 uses an optimised implementation of the IEEE 802.15.4-2015 TSCH (Time-Slotted Channel Hopping) standard to operate efficiently and reliably in unknown environments for more than one year without battery replacement, providing continuous information about the ambient characteristics of the room (such as temperature, humidity and light levels), as well as presence information captured through a motion sensor.
[5]
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, 2017
@article{Fafoutis-2016-spl, title = {Privacy Leakage of Physical Activity Levels in Wireless Embedded Wearable Systems}, author = {Xenofon Fafoutis and Letizia Marchegiani and Georgios Papadopoulos and Robert Piechocki and Theo Tryfonas and George Oikonomou}, year = {2017}, doi = {10.1109/LSP.2016.2642300}, oa-url = {http://research-information.bristol.ac.uk/en/publications/privacy-leakage-of-physical-activity-levels-in-wireless-embedded-wearable-systems(4394b8d7-d8fb-4c6e-a91e-06fb9cab6c30).html}, journal = {Signal Processing Letters}, issn = {1070-9908}, publisher = {IEEE}, volume = {24}, number = {2}, pages = {136--140}, gsid = {18301989522027990431}, abstract = {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<br/>mitigates the leakage of this private information.} }
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.
2016
[4]
@INPROCEEDINGS{Elsts-2016-SenseApp, title = {Microsecond-Accuracy Time Synchronization Using the IEEE 802.15.4 TSCH Protocol}, author = {Atis Elsts and Simon Duquennoy and Xenofon Fafoutis and George Oikonomou and Robert Piechocki and Ian Craddock}, year = {2016}, month = nov, booktitle = {Proc. IEEE SenseApp}, gsid = {11807852472963901506}, publisher = {IEEE}, oa-url = {https://research-information.bristol.ac.uk/en/publications/microsecondaccuracy-time-synchronization-using-the-ieee-802154-tsch-protocol(2e47abe7-60e9-48a7-9f09-9fe7f4859ccb).html}, abstract = {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\%.} }
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\%.
[3]
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 WF-IoT, 2016
@INPROCEEDINGS{Papadopoulos-2016-wfiot, title = {Guard Time Optimisation and Adaptation for Energy Efficient Multi-hop {TSCH} Networks}, author = {Georgios Papadopoulos and Alexandros Mavromatis and Xenofon Fafoutis and Nicolas Montavont and Robert Piechocki and Theo Tryfonas and George Oikonomou}, year = {2016}, booktitle = {Proc. IEEE WF-IoT}, oa-url = {http://research-information.bristol.ac.uk/en/publications/guard-time-optimisation-and-adaptation-for-energy-efficient-multihop-tsch-networks(e72d25b2-2193-4b8b-ad01-9a12392e624e).html}, doi = {10.1109/WF-IoT.2016.7845475}, publisher = {IEEE}, abstract = {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.} }
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.
[2]
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, ser. LNICST, pp. 56-63, 2016
@INPROCEEDINGS{Papadopoulos-2016-interiot-1, title = {Guard Time Optimisation for Energy Efficiency in IEEE 802.15.4-2015 TSCH Links}, author = {Georgios Papadopoulos and Alexandros Mavromatis and Xenofon Fafoutis and Robert Piechocki and Theo Tryfonas and George Oikonomou}, year = {2016}, pages = {56--63}, publisher = {Springer}, booktitle = {2nd EAI International Conference on Interoperability in IoT}, doi = {10.1007/978-3-319-52727-7_8}, oa-url = {http://research-information.bristol.ac.uk/en/publications/guard-time-optimisation-for-energy-efficiency-in-ieee-8021542015-tsch-links(fe063bf4-68c0-45c5-a312-142a4faf0808).html} volume = {190}, series = {LNICST}, abstract = {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.} }
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.
[1]
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 WF-IoT, 2016
@INPROCEEDINGS{Margelis-2016-wfiot, title = {Practical Limits of the Secret Key-Capacity for IoT Physical Layer Security}, author = {George Margelis and Xenofon Fafoutis and Robert Piechocki and George Oikonomou and Theo Tryfonas and Paul Thomas}, year = {2016}, booktitle = {Proc. IEEE WF-IoT}, publisher = {IEEE}, oa-url = {http://research-information.bristol.ac.uk/en/publications/practical-limits-of-the-secret-keycapacity-for-iot-physical-layer-security(ae76486e-ce30-440c-af6d-d6a16aa57140).html}, doi = {10.1109/WF-IoT.2016.7845415}, gsid = {10887200623356750520}, abstract = {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.} }
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.
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