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Item type:Publication, Access status: without files , QMA: A resource-efficient, q-learning-based multiple access scheme for the IIoT(2021-07); Many MAC protocols for the Industrial Internet of Things, such as IEEE 802.15.4 and its extensions, require contention-based channel access for management traffic, e.g., for slot (de)allocations and broadcasts. In many cases, subtle but hidden patterns characterize this secondary traffic, but present contention-based protocols are unaware of these patterns and therefore cannot exploit them. Especially in dense networks, these protocols often do not provide sufficient throughput and reliability for primary traffic, i.e., they cannot allocate transmission slots in time. In this paper, we propose QMA, a contention-based multiple access scheme based on Q-learning. It dynamically adjusts transmission times to avoid collisions by learning patterns in contention-based traffic. We show that QMA solves the hidden node problem without the overhead for RTS/CTS messages and, for example, increases throughput from 10 packets/s to 50 packets/s in a hidden three-node scenario without sacrificing reliability. Additionally, QMA's scalability is evaluated in a realistic scenario for slot (de)allocation in IEEE 802.15.4 DSME, where it achieves up to twice more slot (de)allocations per second.Publicationtype: Conference Paper54 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Performance Analysis of the Slot Allocation Handshake in IEEE 802.15.4 DSMEWireless mesh networks using IEEE 802.15.4 are getting increasingly popular for industrial applications because of low energy consumption and low maintenance costs. The IEEE 802.15.4 standard introduces DSME (Deterministic and Synchronous Multi-channel Extension). DSME uses time-slotted channel access to guarantee timely data delivery, multi-channel communication, and frequency hopping to mitigate the effects of external interferences. A distinguishing feature of DSME is its flexibility and adaptability to time-varying network traffic and to changes in the network topology. In this paper we evaluate the ability of DSME to adapt to time-varying network traffic. We examine the limits for slot allocation rates for different topologies. The evaluation is performed with openDSME, an open-source implementation of DSME.Publicationtype: Conference Paper186 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Live Monitoring and Remote Control of OMNeT++ SimulationsUsing event-based simulations is an excellent method for demonstrating and learning the functionality of computer networks. OMNeT++ provides many features for building and analyzing networks and is widely used in research and teaching. It is, however, difficult to influence a running simulation and the interfaces are more optimized for in-depth analyses so it is easy to get distracted from the main point of interest. This motivation led to the development of a remote interface for the OMNeT++ simulator that facilitates live modifications of parameters as well as monitoring of events. It is based on web technologies and allows for convenient creation of customized interactive interfaces for conferences, fairs, or teaching environments.Publicationtype: Journal Article185 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , openDSME: Reliable Time-Slotted Multi-Hop Communication for IEEE 802.15.4Using wireless sensor and actuator networks in industrial applications promises timely and fine-grained feedback and control of plants. However, these applications call for very high reliability that cannot be fulfilled with contention-based medium access. Therefore, the IEEE 802.15.4 standard was extended with multiple time-slotted as well as frequency-agile medium access techniques. The Deterministic and Synchronous Multi-Channel Extension (DSME) is of particular interest due to its extensive set of standardized methods for distributed slot management. This chapter presents openDSME, a comprehensive implementation of DSME to be used in the OMNeT++ simulator as well as on real-life wireless sensor nodes. The main features of DSME are presented, together with implementation details of openDSME. The chapter concludes with a step-by-step tutorial to get started with openDSME.Publicationtype: Journal Article164 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Delay-bounded scheduling in IEEE 802.15.4e DSME using linear programming(2019-05); The Deterministic and Synchronous Multi-Channel Extension (DSME) protocol is a recent amendment to the IEEE 802.15.4 standard. It combines contention-based and time-division medium access, offers channel diversity, and is aimed to support IIoT applications with stringent requirements in terms of timeliness and reliability. In this paper, we show how to configure DSME for a given data collection task. This includes the definition of the slot and frame length and the slot and channel schedule. We formulate different scheduling strategies as linear programs minimizing latency and energy. We verify our results through theoretical analysis and simulations and compare them with state-of-the-art scheduling algorithms. The results indicate a reduced delay of up to 80% for deep networks while also increasing reliability. Additionally, the proposed scheduling strategies significantly reduce the required buffer size.Publicationtype: Conference Paper200 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Scalable wireless multi-hop networks for industrial applications(2019); Wireless technology promises flexible and cost-efficient machine-to-machine communication. However, high packet loss can emerge from simultaneous transmissions of many devices, undermining the reliability required for industrial applications. This thesis analyzes and develops techniques for time-slotted multi-hop communication with focus on IEEE 802.15.4 DSME. In a holistic approach, simulations, formal and analytical analyses and testbed experiments are combined, concluding the utility of the proposed methods. For future usage in research and real-world deployments, openDSME is developed as open-source implementation of DSME and application-specific insights are provided.Publicationtype: Doctoral Thesis914 2810 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , An analytical model for wireless mesh networks with collision-free TDMA and finite queuesWireless mesh networks are a promising technology for connecting sensors and actuators with high flexibility and low investment costs. In industrial applications, however, reliability is essential. Therefore, two time-slotted medium access methods, DSME and TSCH, were added to the IEEE 802.15.4 standard. They allow collision-free communication in multi-hop networks and provide channel hopping for mitigating external interferences. The slot schedule used in these networks is of high importance for the network performance. This paper supports the development of efficient schedules by providing an analytical model for the assessment of such schedules, focused on TSCH. A Markov chain model for the finite queue on every node is introduced that takes the slot distribution into account. The models of all nodes are interconnected to calculate network metrics such as packet delivery ratio, end-to-end delay, and throughput. An evaluation compares the model with a simulation of the Orchestra schedule. The model is applied to Orchestra as well as to two simple distributed scheduling algorithms to demonstrate the importance of traffic-awareness for achieving high throughput.Publicationtype: Journal ArticleScopus© Citations 3 587 622 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A dual-radio approach for reliable emergency signaling in critical infrastructure assets with large wireless networks(2018-06); ; Wireless communications techniques are finding their way into industrial applications, but commercial wireless technologies lack the dependability required for critical applications in very large networks. In many wireless-controlled industrial facilities, safety regulations mandate real-time communications for tasks such as emergency shutdowns. This requires a wireless communications architecture that supports the coexistence of non-real-time and real-time tasks. To address this requirement, this paper proposes an architecture that augments a wireless mesh network with a unidirectional long-range communications system. Various configuration parameters of the system, including its security features, are optimized. Additionally, a physical realization of the architecture is evaluated using a series of experiments, including some performed on a real solar tower power plant. The experimental results demonstrate that the extension of a wireless mesh network with a unidirectional long-range communications system provides safety and scalability for industrial applications while promoting cost effectiveness and energy efficiency.Publicationtype: Journal Article99 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Constructing customized multi-hop topologies in dense wireless network testbedsTestbeds are a key element in the evaluation of wireless multi-hop networks. In order to relieve researchers from the hassle of deploying their own testbeds, remotely controllable testbeds, such as the FIT/IoT-LAB, are built. However, while the IoT-LAB has a high number of nodes, they are deployed in constraint areas. This, together with the complex nature of radio propagation, makes an ad-hoc construction of multi-hop topologies with a high number of hops difficult. This work presents a strategic approach to solve this problem and proposes algorithms to generate topologies with desired properties. The implementation is evaluated for the IoT-LAB testbeds and is provided as open-source software. The results show that preset topologies of various types can be built even in dense testbeds.Publicationtype: Conference Paper174