| 1. |
- Harms, Laura, 1991
(författare)
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Adaptive and Resource-Efficient Systems for the Internet of Things
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the growing number of Internet of Things (IoT) devices and the emergence of the Industrial Internet of Things (IIoT), there is a growing demand for adaptive and resource-efficient wireless communication protocols and systems. Industrial networks play a crucial role in monitoring pipelines and facilitating communication among collaborating devices, such as robots in a smart factory. These applications are safety-critical and necessitate long-term reliable and low-latency communication. However, the rising number of IoT communicating devices and deployments increasingly congests the wireless medium, which leads to interference and makes the latency and reliability requirements more challenging to accomplish. Current solutions and protocols are incapable of addressing these evolving demands. Therefore, there is a need for novel communication protocols and systems capable of dynamically adapting to unforeseen interference and changes in the wireless medium. In this thesis, we design, implement, and evaluate protocols, systems, and evaluation infrastructures tailored for modern IoT solutions. To facilitate long-term stable communication within centrally scheduled IEEE 802.15.4 Time-Slotted Channel Hopping (TSCH) networks, we propose a centralized scheduler and a flow-based retransmission strategy. This strategy allocates retransmissions to be utilized at any node within a communication flow, thereby enhancing resilience against unforeseen interference. We then introduce Autobahn , a communication protocol that integrates opportunistic routing and synchronous transmissions with TSCH to mitigate local wideband interference while keeping latency to a minimum. With TBLE , we bring TSCH to Bluetooth Low Energy (BLE), further reducing latency without compromising reliability. To provide comprehensive insights into distributed wireless communication protocols on testbeds, we propose Grace , a low-cost time-synchronized General-Purpose Input/Output (GPIO) tracing system for existing testbeds. Finally, we demonstrate with BlueSeer that a device can recognize its environment—such as home, office, restaurant, or street—solely from received ambient BLE signals using an embedded machine learning model. BlueSeer enables small IoT devices like wireless headphones to adapt their behaviors to the surrounding environment.
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| 2. |
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| 3. |
- Harms, Laura, 1991
(författare)
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C-TSCH: A Centralized Scheduler for TSCH
- 2019
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Ingår i: International Conference on Embedded Wireless Systems and Networks. - 2562-2331. ; , s. 314-315
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Konferensbidrag (refereegranskat)abstract
- We present a centralized scheduler for reliable communications in low-power wireless TSCH networks. This scheduler enables us to introduce a novel centralized routing approach not dependent on existing distributed solutions like RPL.
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| 4. |
- Harms, Laura, 1991, et al.
(författare)
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Competition: Centrally Scheduled Low-Power Wireless Networking for Dependable Data Collection
- 2019
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Ingår i: International Conference on Embedded Wireless Systems and Networks. - 2562-2331. ; 2019, s. 300-301
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Konferensbidrag (refereegranskat)abstract
- For low-power wireless networks, it is important to survive interference to be usable for Industrial Internet-of-Things (IIoT) applications. Distributed flooding protocols like Glossy or Chaos have shown that they can meet the expectations of surviving interference and node failures. However, non-distributed, centralized schedulers are favorable for IIoT but are not used yet in these environments. In this paper, we explore the use of centralized schedulers for low-power wireless networks to achieve robustness in data collection applications.
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| 5. |
- Harms, Laura, 1991, et al.
(författare)
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Grace: Low-Cost Time-Synchronized GPIO Tracing for IoT Testbeds
- 2022
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Ingår i: Proceedings - 18th Annual International Conference on Distributed Computing in Sensor Systems, DCOSS 2022. ; , s. 9-16
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Konferensbidrag (refereegranskat)abstract
- Testbeds have become a vital tool for evaluating and benchmarking applications and algorithms in the Internet of Things (IoT). Testbeds commonly consist of low-power IoT devices augmented with observer nodes providing control, logging, and often also power-profiling. Today, the research community operates numerous testbeds, sometimes with hundreds of IoT nodes, to allow for detailed and large-scale evaluation. Most testbeds, however, lack opportunities for tracing distributed program execution with high accuracy in time, for example, via minimally invasive, distributed GPIO tracing. And the ones that do, like Flocklab, are built from custom hardware, which is often too complex, inflexible, or expensive to use for other research groups.This paper closes this gap and introduces Grace, a low-cost, retrofittable, distributed, and time-synchronized GPIO tracing system built from off-the-shelf components, costing less than €20 per node. Grace extends observer nodes in a testbed with (1) time-synchronization via wireless sub-GHz transceivers and (2) logic analyzers for GPIO tracing and logging, enabling time-synchronized GPIO tracing at a frequency of up to 8 MHz. We deploy Grace in a testbed and show that it achieves an average time synchronization error between nodes of 1.53 µs.
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| 6. |
- Harms, Laura, 1991, et al.
(författare)
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Grace: Low-cost time-synchronized GPIO tracing for IoT testbeds
- 2023
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Ingår i: Computer Networks. - : Elsevier BV. - 1389-1286. ; 228
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Tidskriftsartikel (refereegranskat)abstract
- Testbeds have become a vital tool for evaluating and benchmarking applications and algorithms in the Internet of Things (IoT). IoT testbeds commonly consist of low-power IoT devices augmented with observer nodes providing control, debugging, logging, and often also power-profiling capabilities. Today, the research community operates numerous testbeds, sometimes with hundreds of IoT nodes, to allow for detailed and large-scale evaluation. Most testbeds, however, lack opportunities for tracing distributed program execution with high accuracy in time, for example, via minimally invasive, distributed GPIO tracing. And the ones that do, like Flocklab, are built from custom hardware, which is often too complex, inflexible, or expensive to use for other research groups. This paper closes this gap and introduces Grace, a low-cost, retrofittable, distributed, and time-synchronized GPIO tracing system built from off-the-shelf components, costing less than €20 per node. Grace extends observer nodes in a testbed with (1) time-synchronization via wireless sub-GHz transceivers and (2) logic analyzers for GPIO tracing and logging, enabling time-synchronized GPIO tracing at a frequency of up to 8 MHz. We deploy Grace in a testbed and evaluate it, showing that it achieves an average time synchronization error between nodes of 1.53 μs using a single time source, and 15.3 μs between nodes using different time sources, sufficient for most IoT applications.
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| 7. |
- Harms, Laura, 1991
(författare)
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Long-Term Stable Communication in Centrally Scheduled Low-Power Wireless Networks
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the emergence of the Internet of Things (IoT), more devices are connected than ever before. Most of these communicate wirelessly, forming Wireless Sensor Networks. In recent years, there has been a shift from personal networks, like Smart Home, to industrial networks. Industrial networks monitor pipelines or handle the communication between robots in factories. These new applications form the Industrial Internet of Things (IIoT). Many industrial applications have high requirements for communication, higher than the requirements of common IoT networks. Communications must stick to hard deadlines to avoid harm, and they must be highly reliable as skipping information is not a viable option when communicating critical information. Moreover, communication has to remain reliable over longer periods of time. As many sensor locations do not offer a power source, the devices have to run on battery and thus have to be power efficient. Current systems offer solutions for some of these requirements. However, they especially lack long-term stable communication that can dynamically adapt to changes in the wireless medium. In this thesis, we study the problem of stable and reliable communication in centrally scheduled low-power wireless networks. This communication ought to be stable when it can dynamically adapt to changes in the wireless medium while keeping latency at a minimum. We design and investigate approaches to solve the problem of low to high degrees of interference in the wireless medium. We propose three solutions to overcome interference: MASTER with Sliding Windows brings dynamic numbers of retransmissions to centrally scheduled low-power wireless networks, OVERTAKE allows to skip nodes affected by interference along the path, and AUTOBAHN combines opportunistic routing and synchronous transmissions with the Time-Slotted Channel Hopping (TSCH) MAC protocol to overcome local wide-band interference with the lowest possible latency. We evaluate our approaches in detail on testbed deployments and provide open-source implementations of the protocols to enable others to build their work upon them.
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| 8. |
- Harms, Laura, 1991, et al.
(författare)
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MASTER: Long-Term Stable Routing and Scheduling in Low-Power Wireless Networks
- 2020
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Ingår i: 16TH ANNUAL INTERNATIONAL CONFERENCE ON DISTRIBUTED COMPUTING IN SENSOR SYSTEMS (DCOSS 2020). - 2325-2936. ; , s. 86-94
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Konferensbidrag (refereegranskat)abstract
- Wireless Sensor-Actuator Networks (WSANs) are an important driver for the Industrial Internet of Things (IIoT) as they easily retrofit existing industrial infrastructure. Industrial applications require these networks to provide stable communication with high reliability and guaranteed low latency. A common way is using a central scheduler to plan transmissions and routes so that all packets are delivered before a deadline. However, existing centralized schedulers are only able to achieve high reliability in the absence of interference. This limitation lowers the feasibility of using centralized schedulers in most environments susceptible to interference. This paper addresses the challenge of stable, centrally scheduled communication in low-power wireless networks susceptible to interference. We introduce MASTER, a centralized scheduler and router, for IEEE 802.15.4 TSCH (Time-Slotted Channel Hopping). MASTER uses Sliding Windows, a novel transmission strategy, which builds on flow-based retransmissions instead of link-based ones. We show in our experimental evaluation that MASTER with Sliding Windows achieves routing and scheduling stability for over 24 hours with end-to-end reliability of over 99.6%. Moreover, we show that MASTER outperforms Orchestra, a state-of-the-art autonomous scheduler, in terms of latency by a factor of 8 while achieving similar reliability under a slight duty-cycle increase.
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| 9. |
- Harms, Laura, 1991
(författare)
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Modulation Schemes in Ambient Backscatter Communication
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a low-cost backscatter system using off the-shelf components. It uses simple modulation schemes and is usable with a constant carrier as well as with ambient television signals as carrier. The evaluation of the system shows that ranges of up to 225 m are coverable in line-of-sight environments using a constant carrier. Furthermore, it is usable with ambient TV signals with bit error rates as low as 10^−3. These results show that this backscatter system outperforms state-of-art backscatter systems.
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| 10. |
- Harms, Laura, 1991, et al.
(författare)
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Opportunistic Routing and Synchronous Transmissions Meet TSCH
- 2021
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Ingår i: Proceedings - Conference on Local Computer Networks, LCN. ; 2021-October, s. 107-114
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Konferensbidrag (refereegranskat)abstract
- Low-power wireless networking commonly uses either Time-Slotted Channel Hopping (TSCH), synchronous transmissions, or opportunistic routing. All three of these different, orthogonal approaches strive for efficient and reliable communication but follow different trajectories. With this paper, we combine these concepts into one protocol: AUTOBAHN. AUTOBAHN merges TSCH scheduling with opportunistically routed, synchronous transmissions. This opens the possibility to create long-term stable schedules overcoming local interference. We prove the stability of schedules over several days in our experimental evaluation. Moreover, AUTOBAHN outperforms the autonomous scheduler Orchestra under interference in terms of reliability by 13.9 percentage points and in terms of latency by a factor of 9 under a minor duty cycle increase of 2.1 percentage points.
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