| 1. |
- Barac, Filip
(författare)
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Error mitigation in industrial wireless sensor networks : Corrupted packet forensics and recovery
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless sensor networks (WSN) are gradually penetrating the industrial automation domain. This process is, however, inhibited by a number of challenges that need to be considered and addressed before WSN can serve the most demanding industrial applications. In the context of process automation, existing technology can only serve the three least critical application classes related to non-critical monitoring of slowly-changing physical variables. The main issue in that respect is the insufficient communication timeliness and reliability, caused by the influence of harsh radio environment and the infeasibility of applying advanced communication techniques, due to the poor computational power of low-cost specialized hardware. The goal of this work is to improve wireless communication reliability in industrial environments, where the proposed solutions are generally applicable to other WSN domains as well as radio environments. This research is based on the notion that corrupt packets contain valuable channel state information that can be leveraged to improve communication robustness. The research methodology used in this work is rather unconventional, compared to existing research, but also highly intuitive, bearing in mind that counteracting a phenomenon requires a thorough knowledge of its properties. In order to rectify the aforementioned challenges, this work makes the following three contributions. The first contribution is a comprehensive analysis of communication errors recorded in practically relevant scenarios in a number of industrial environments. The related literature is seemingly rich, but essentially poor, due to inadequate measurement objectives, environments, and scenarios. The main research outcome of this measurement campaign is a set of practically relevant conclusions, which can be used for the design of coding, interleaving and packet recovery schemes. The second contribution is the design of two packet recovery schemes, based on the knowledge about error patterns obtained in the industrial measurement campaign. The first scheme is a proposal for redefinition of the IEEE 802.15.4 physical layer, where digital errors are counteracted at the earliest stage in the receiver chain. The second scheme exploits the determinism in packet structure inherent to industrial communication. Both schemes significantly improve the correctability of corrupted packets received. The third contribution is a channel diagnostics algorithm that determines whether a packet was corrupt by multipath fading and attenuation or by wireless local area network interference. The algorithm is derived from the error traces collected in three industrial environments and tested at a fourth, previously unused, industrial site. The results of live tests verify the ability of the proposed algorithm to promptly reestablish communication after a sudden deterioration of channel quality.
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| 2. |
- Dobslaw, Felix, 1983-
(författare)
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End-to-End Quality of Service Guarantees for Wireless Sensor Networks
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless sensor networks have been a key driver of innovation and societal progressover the last three decades. They allow for simplicity because they eliminate ca-bling complexity while increasing the flexibility of extending or adjusting networksto changing demands. Wireless sensor networks are a powerful means of fillingthe technological gap for ever-larger industrial sites of growing interconnection andbroader integration. Nonetheless, the management of wireless networks is difficultin situations wherein communication requires application-specific, network-widequality of service guarantees. A minimum end-to-end reliability for packet arrivalclose to 100% in combination with latency bounds in the millisecond range must befulfilled in many mission-critical applications.The problem addressed in this thesis is the demand for algorithmic support forend-to-end quality of service guarantees in mission-critical wireless sensor networks.Wireless sensors have traditionally been used to collect non-critical periodic read-ings; however, the intriguing advantages of wireless technologies in terms of theirflexibility and cost effectiveness justify the exploration of their potential for controland mission-critical applications, subject to the requirements of ultra-reliable com-munication, in harsh and dynamically changing environments such as manufactur-ing factories, oil rigs, and power plants.This thesis provides three main contributions in the scope of wireless sensor net-works. First, it presents a scalable algorithm that guarantees end-to-end reliabilitythrough scheduling. Second, it presents a cross-layer optimization/configurationframework that can be customized to meet multiple end-to-end quality of servicecriteria simultaneously. Third, it proposes an extension of the framework used toenable service differentiation and priority handling. Adaptive, scalable, and fast al-gorithms are proposed. The cross-layer framework is based on a genetic algorithmthat assesses the quality of service of the network as a whole and integrates the phys-ical layer, medium access control layer, network layer, and transport layer.Algorithm performance and scalability are verified through numerous simula-tions on hundreds of convergecast topologies by comparing the proposed algorithmswith other recently proposed algorithms for ensuring reliable packet delivery. Theresults show that the proposed SchedEx scheduling algorithm is both significantlymore scalable and better performing than are the competing slot-based schedulingalgorithms. The integrated solving of routing and scheduling using a genetic al-vvigorithm further improves on the original results by more than 30% in terms of la-tency. The proposed framework provides live graphical feedback about potentialbottlenecks and may be used for analysis and debugging as well as the planning ofgreen-field networks.SchedEx is found to be an adaptive, scalable, and fast algorithm that is capa-ble of ensuring the end-to-end reliability of packet arrival throughout the network.SchedEx-GA successfully identifies network configurations, thus integrating the rout-ing and scheduling decisions for networks with diverse traffic priority levels. Fur-ther, directions for future research are presented, including the extension of simula-tions to experimental work and the consideration of alternative network topologies.
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| 3. |
- Farag, Hossam
(författare)
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Enabling Industrial IoT Applications : Supporting Reliable and Real-Time Data Delivery
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Industrial Internet of Things (IIoT) has become a promising technology for the improvement of the productivity, efficiency, and intelligence of the manufacturing process. Industrial Wireless Sensor Networks (IWSNs) represent a main pillar of IIoT to support communications within the field network level. For several IIoT applications, IWSNs are defined by strict communication requirements in terms of latency and reliability to support the proper functioning of the industrial system and avoid production loss. However, there are many challenges in efficiently satisfying these requirements. The key challenges investigated in this thesis are related to the shortcomings of the existing IWSN standards to enable timely delivery of aperiodic critical data, support traffic differentiation, and maintain reliable end-to-end communications. The overall objective of this work is to improve the reliability and real-time communication at the field network level in IIoT applications, particularly in process automation scenarios. Specifically, the proposed solutions represent improvements within the data-link and network layers of the IWSN protocol stack. The work in this thesis introduces the following contributions. The first part of the thesis focuses on improving real-time delivery for critical traffic and enabling traffic differentiation for mixed-criticality systems. The contribution in this part comprises three approaches. The first approach introduces a deterministic priority-based channel access mechanism for emergency data in time- and mission-critical applications. The approach is based on a dynamic deadline-aware schedule to provide a delay-bounded performance for the unpredictable emergency traffic along with efficient channel utilization. In the second approach, a priority-based wireless fieldbus protocol is proposed to enable traffic differentiation in mixed-criticality systems, where each traffic flow is given a transmission priority according to its corresponding criticality level. The third approach presents an optimized retransmission scheme to maximize the probability that an emergency packet is successfully delivered within its deadline bound. The results of the proposed schemes prove their effectiveness in providing real-time delivery for critical traffic and efficient service differentiation for mixed-criticality systems. The second part of the thesis introduces a routing framework to improve the connectivity and the end-to-end communication reliability of 6TiSCH networks. The proposed solutions in this part are mainly designed on the basis of the standard Routing Protocol for Low-Power and Lossy Networks (RPL). The proposed framework comprises the following approaches: 1) a reliable mobility-aware routing scheme to support node connectivity and reliable routing in mobile 6TiSCH networks, 2) a congestion control and detection strategies to enhance packet delivery performance under imbalanced network and heavy load scenarios, 3) a hybrid multi-cast method to maintain downlink connectivity and mitigate routing memory limitations in large-scale 6TiSCH networks. The conducted performance evaluations prove the effectiveness of the proposed approaches to enhance network performance in terms of reliability and delay metrics. The proposed approaches manage to improve routing performance of 6TiSCH networks in terms of connectivity and end-to-end data delivery, which in turn improves the real-time communication in IIoT.
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| 4. |
- Gidlund, Mikael
(författare)
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Design and Performance of Packet Retransmission Diversity Scheme for Wireless Networks
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High data-rate wireless access systems are currently under discussion since the demand for wireless multimedia communication is rapidly increasing due to strong advances in wireless Internet services. Reliable high-speed data communications is one of the major challenges with regards to harsh conditions. With the necessity for high data rates, linear multi-level modulation schemes are becoming more and more important in wireless communication systems since they are bandwidth efficient. In this thesis protocols are designed and evaluated which improve system performance by combining ARQ-induced retransmissions through multipath channels in order to reduce the latency and improve the system throughput. The starting point is to show that the employment of simple packet combining schemes to wireless LANs such as IEEE 802.11, can achieve a considerable performance gain with the addition of only a small increase in complexity. A low-complexity method for enhancing and exploiting retransmission diversity by varying the bit-to-symbol mapping for each retransmission of a packet is evaluated. The selected mappings are chosen in order to maximize a bit log likelihood ratio (LLR) based metric. An ARQ scheme is also proposed, which combines retransmissions and bandwidth efficient multi-level modulation techniques with a change in the symbol mapping for every retransmission. The main idea behind this proposal is to take advantage of the extra dimension provided by a retransmission diversity scheme in improving the power efficiency if the used modulation without altering the diversity order of the system. Considering the overall scheme as one entity it is possible to obtain a transmission scheme able to perform very well in both additive Gaussian and fading channels without increase in receiver complexity. Finally, multiple antenna systems with ARQ functionality are evaluated. It has been established that using multiple antennas at both the transmitter and receiver along with intelligent signal design enables us to achieve better reliability as well as increase the transmission rate. In this thesis a space-time block coded hybrid ARQ scheme is considered which exploits both the spatial and time diversity of the MIMO channel. A bit-to-symbol mapping ARQ scheme suitable for multiple antenna systems is also considered.
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| 5. |
- Shen, Wei
(författare)
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A Protocol Framework for Adaptive Real-Time Communication in Industrial Wireless Sensor and Actuator Networks
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Low-power and resource-constrained wireless technology has been regarded as an emerging technology that introduces a paradigm shift in a wide range of applications such as industrial automation, smart grid, home automation and so on. The automation industry has significant contributions to economic revenues, job opportunities and world-class research. The low-power and resource-constrained wireless technology has brought new opportunity and challenges for industrial automation. The solutions of such wireless technology offer benefits in relation to lower cost and more flexible deployments/maintenances than the wired solutions, and new applications that are not possible with wired communication. However, these wireless solutions have been introducing new challenges. Wireless links are inherently unreliable, especially in industrial harsh environment, and wireless interference makes the problem even worse. Low-power consumption is required and real-time communication is generally crucial in industrial automation applications.This research work addresses that industrial wireless sensor and actuator network (IWSAN) should even be designed to provide service differentiation for wireless medium access and adapt to link dynamics for scheduling algorithms on top of real-time services. Specifically, exceeding the required delay bound for unpredictable and emergency traffic in industrial automation applications could lead to system instability, economic and material losses, system failure and, ultimately, a threat to human safety. Therefore, guaranteeing the timely delivery of the IWSAN critical traffic and its prioritization over regular traffic (e.g. non-critical monitoring traffic) is a significant topic. In addition, the state-of-the-art researches address a multitude of objectives for scheduling algorithms in IWSAN. However, the adaptation to the dynamics of a realistic wireless sensor network has not been investigated in a satisfactory manner. This is a key issue considering the challenges within industrial applications, given the time-constraints and harsh environments.In response to those challenges, a protocol framework for adaptive real-time communication in IWSAN is proposed. It mainly consists of a priority-based medium access protocol (MAC) and its extension for routing critical traffic, a hybrid scheme for acyclic traffic, and adaptive scheduling algorithms. To the best of our knowledge, the priority-based MAC solution is the first priority-enhanced MAC protocol compatible with industrial standards for IWSAN. The proposed solutions have been implemented in TinyOS and evaluated on a test-bed of Telosb motes and the TOSSIM network simulator. The experimental results indicate that the proposed priority-based solutions are able to efficiently handle different traffic categories and achieve a significant improvement in the delivery latency. The hybrid scheme for acyclic traffic increases the throughput and reduces the delay compared to the current industrial standards. Numerical results show that the adaptive scheduling algorithms improve the quality of service for the entire network. They achieve significant improvements for realistic dynamic wireless sensor networks when compared to existing scheduling algorithms with the aim to minimize latency for real-time communication.
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