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Enabling Sustainable Networked Embedded Systems
Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication. (UNO)
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

Networked Embedded Systems (NES) are small energy-constrained devices typically with sensors, radio and some form of energy storage. The past several years have seen a rapid growth of applications of NES, with several predictions stating billions of devices deployed in the near future. As NES are deployed at large scale, a growing challenge is to support NES for long periods of time without negatively impacting their physical or the radio environment, i.e., in a sustainable manner. In this dissertation, we identify intertwined challenges that affect the sustainability of NES systems: co-existence on the shared wireless spectrum; energy consumption; and the cost of the deployment and maintenance. We identify research directions to overcome these challenges and address them through the six research papers.

Firstly, NES have to co-exist with other wireless devices that operate on the shared wireless spectrum. A growing number of devices contending for the spectrum is challenging and leads to increased interference among them. To enable NES to co-exist with other wireless devices, we investigate the use of electronically steerable directional antennas (ESD). ESD antennas allow software-based control of the direction of maximum antenna gain on a per-packet basis and can operate within the severe energy constraints of NES. In the dissertation, we demonstrate that ESD antennas allow solutions that outperform the state-of-the-art in sensing and communication in wireless sensor networks while supporting operations on a single wireless channel reducing the contention on the shared wireless spectrum.

Secondly, we explore the emerging area of visible light sensing and communication to avoid the crowded radio frequency spectrum. Visible light can be an alternative or a complement to radio frequency for sensing and communication. We make two contributions in the dissertation to make the visible light communication a viable option for NES. We design a novel visible light sensing architecture that supports sensing and communication at tens of microwatts of power. An ultra-low power consumption can make visible light sensing systems pervasive. Our second contribution brings high-speed visible light communication to energy-constrained NES. We design a novel visible light receiver that adapts to the dynamics of changing light conditions, and the energy constraints of the host device while supporting a throughput comparable to radio frequency standards for NES. Through our contribution, we take a significant step to enable visible light-based sustainable NES.

Finally, replacing batteries on sensor nodes significantly affects the sustainability of NES. Battery-free sensors that harvest small amounts of energy from the ambient environment have a great potential to enable pervasive deployment of NES. To support wide-area deployments of battery-free sensors, we develop an ultra-low power and long-range communication mechanism. We demonstrate the ability to communicate to distances as long as a few kilometres while consuming tens of microwatts at the sensor device. Our contributions pave the way for a wide-area deployment of battery-free sustainable NES.

Through the contributions made in the dissertation, we take a significant step towards the broader goal of sustainable NES. The work included in the dissertation significantly improves the state-of-the-art in NES, in some case by orders of magnitude.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. , p. 52
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1648
Keyword [en]
Wireless Sensor Network; Energy harvesting; backscatter; RFID; Sensors
National Category
Computer Systems
Research subject
Computer Science with specialization in Computer Communication
Identifiers
URN: urn:nbn:se:uu:diva-346267ISBN: 978-91-513-0279-9 (print)OAI: oai:DiVA.org:uu-346267DiVA, id: diva2:1190906
Public defence
2018-05-07, 2446, ITC, Lägerhyddsvägen 2, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2018-04-18 Created: 2018-03-16 Last updated: 2018-04-18
List of papers
1. Directional Transmissions and Receptions for High-throughput Bulk Forwarding in Wireless Sensor Networks
Open this publication in new window or tab >>Directional Transmissions and Receptions for High-throughput Bulk Forwarding in Wireless Sensor Networks
2015 (English)In: Proceedings of the 13th ACM Conference on Embedded Networked Sensor Systems, 2015, p. 351-364Conference paper, Published paper (Refereed)
Abstract [en]

We present DPT: a wireless sensor network protocol for bulk traffic that uniquely leverages electronically switchable directional (ESD) antennas. Bulk traffic is found in several scenarios and supporting protocols based on standard antenna technology abound. ESD antennas may improve performance in these scenarios; for example, by reducing channel contention as the antenna can steer the radiated energy only towards the intended receivers, and by extending the communication range at no additional energy cost. The corresponding protocol support, however, is largely missing. DPT addresses precisely this issue. First, while the network is quiescent, we collect link metrics across all possible antenna configurations. We use this information to formulate a constraint satisfaction problem (CSP) that allows us to find two multi-hop disjoint paths connecting source and sink, along with the corresponding antenna configurations. Domain-specific heuristics we conceive ameliorate the processing demands in solving the CSP, improving scalability. Second, the routing configuration we obtain is injected back into the network. During the actual bulk transfer, the source funnels data through the two paths by quickly alternating between them. Packet forwarding occurs deterministically at every hop. This allows the source to implicitly "clock" the entire pipeline, sparing the need of proactively synchronizing the transmissions across the two paths. Our results, obtained in a real testbed using 802.15.4-compliant radios and custom ESD antennas we built, indicate that DPT approaches the maximum throughput supported by the link layer, peaking at 214 kbit/s in the settings we test.

Keyword
Directional antennas; Bulk data transmissions; Wireless sensor networks; Electronically controlled antennas
National Category
Computer Systems
Research subject
Computer Science with specialization in Computer Communication
Identifiers
urn:nbn:se:uu:diva-266348 (URN)10.1145/2809695.2809720 (DOI)000380612400028 ()9781450336314 (ISBN)
Conference
The 13th ACM Conference on Embedded Networked Sensor Systems (SenSys 2015), November 1-4, 2015, Seoul, South Korea
Available from: 2015-11-08 Created: 2015-11-08 Last updated: 2018-03-16Bibliographically approved
2. dRTI: Directional Radio Tomographic Imaging
Open this publication in new window or tab >>dRTI: Directional Radio Tomographic Imaging
Show others...
2015 (English)In: Proceedings of the 14th International Conference on Information Processing in Sensor Networks, 2015, p. 166-177Conference paper, Published paper (Refereed)
Abstract [en]

Radio tomographic imaging (RTI) enables device free localisation of people and objects in many challenging environments and situations. Its basic principle is to detect the changes in the statistics of radio signals due to the radio link obstruction by people or objects. However, the localisation accuracy of RTI suffers from complicated multipath propagation behaviours in radio links. We propose to use inexpensive and energy efficient electronically switched directional (ESD) antennas to improve the quality of radio link behaviour observations, and therefore, the localisation accuracy of RTI. We implement a directional RTI (dRTI) system to understand how directional antennas can be used to improve RTI localisation accuracy. We also study the impact of the choice of antenna directions on the localisation accuracy of dRTI and propose methods to effectively choose informative antenna directions to improve localisation accuracy while reducing overhead. Furthermore, we analyse radio link obstruction performance in both theory and simulation, as well as false positives and false negatives of the obstruction measurements to show the superiority of the directional communication for RTI. We evaluate the performance of dRTI in diverse indoor environments and show that dRTI significantly outperforms the existing RTI localisation methods based on omni-directional antennas.

Series
IPSN ’15
National Category
Computer Systems
Identifiers
urn:nbn:se:uu:diva-252426 (URN)10.1145/2737095.2737118 (DOI)
Conference
ACM/IEEE IPSN 2015
Available from: 2015-05-06 Created: 2015-05-06 Last updated: 2018-03-16
3. LoRea: A backscatter architecture that achieves a long communication range
Open this publication in new window or tab >>LoRea: A backscatter architecture that achieves a long communication range
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2017 (English)In: Proc. 15th ACM Conference on Embedded Network Sensor Systems, New York: ACM Press, 2017Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
New York: ACM Press, 2017
National Category
Computer Engineering
Identifiers
urn:nbn:se:uu:diva-335566 (URN)10.1145/3131672.3131691 (DOI)978-1-4503-5459-2 (ISBN)
Conference
SenSys 2017, November 5–8, Delft, The Netherlands
Available from: 2017-11-05 Created: 2017-12-06 Last updated: 2018-03-16Bibliographically approved
4. Towards wide-area backscatter networks
Open this publication in new window or tab >>Towards wide-area backscatter networks
2017 (English)In: Proc. 4th ACM Workshop on Hot Topics in Wireless, New York: ACM Press, 2017, p. 49-53Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
New York: ACM Press, 2017
National Category
Computer Engineering
Identifiers
urn:nbn:se:uu:diva-335565 (URN)10.1145/3127882.3127888 (DOI)978-1-4503-5140-9 (ISBN)
Conference
HotWireless 2017, October 16, Snowbird, UT
Available from: 2017-10-16 Created: 2017-12-06 Last updated: 2018-03-16Bibliographically approved
5. Battery-free Visible Light Sensing
Open this publication in new window or tab >>Battery-free Visible Light Sensing
2017 (English)In: Proc. 4th ACM Workshop on Visible Light Communication Systems, New York: ACM Press, 2017, p. 3-8Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
New York: ACM Press, 2017
National Category
Computer Engineering
Identifiers
urn:nbn:se:uu:diva-335564 (URN)10.1145/3129881.3129890 (DOI)978-1-4503-5142-3 (ISBN)
Conference
VLCS 2017, October 16, Snowbird, UT
Available from: 2017-10-16 Created: 2017-12-06 Last updated: 2018-03-16Bibliographically approved
6. Visible Light Communication for Wearable Computing
Open this publication in new window or tab >>Visible Light Communication for Wearable Computing
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Visible Light Communication (VLC) is emerging as a means to network computing devices that ameliorates many hurdles of radio-frequency (RF) communications, for example, the limited available spectrum. Enabling VLC in wearable computing, however, is challenging because mobility induces unpredictable drastic changes in light conditions, for example, due to reflective surfaces and obstacles casting shadows.We experimentally demonstrate that such changes are so extreme that no single design of a VLC receiver can provide efficient performance across the board. The diversity found in current wearable devices complicates matters. Based on these observations, we present three different designs of VLC receivers that i) are individual orders of magnitude more efficient than the state-of-the-art in a subset of the possible conditions, and ii) can be combined in a single unit that dynamically switches to the best performing receiver based on the light conditions.Our evaluation indicates that dynamic switching incurs minimal overhead, that we can obtain throughput in the order of MBit/s, and at energy costs lower than many RF devices.

National Category
Communication Systems
Research subject
Computer Science with specialization in Computer Communication
Identifiers
urn:nbn:se:uu:diva-346820 (URN)
Available from: 2018-03-21 Created: 2018-03-21 Last updated: 2018-03-23

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