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Item type:Publication, Access status: with files , Adaptive multi-hop networks for industrial applications with dynamically changing traffic(2023); This dissertation explores techniques for adaptive multi-hop networks in the IIoT concerning time-varying, dynamically changing traffic. It demonstrates that efficient transmission of management traffic is crucial for high adaptability in IEEE 802.15.4 DSME, develops several techniques to increase adaptability and validates them through simulations, hardware experiments, and analytical models. In particular, QMA reduces collisions in management traffic by learning when it is feasible to transmit a packet. Sending multiple packets per GTS and group acknowledgments further relieve the management traffic load. Finally, dynamic CAP-reduction enables a fine-grained trade-off between management and data traffic.Publicationtype: Doctoral Thesis117 951 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Machine learning-based dynamic spectrum access for aircraft-to-aircraft communication under coexistence with legacy radio systems(2022-06-30)Spectrum scarcity is viewed as one of the key obstacles in the area of wireless communications. The lack of available unlicensed resources is impairing the development of newer and more modern communications systems. This is the case of L-band Digital Aeronautical Communications System (LDACS), an innovative air communication system that aims to use the part of the frequency spectrum licensed by Distance Measuring Equipment (DME), a legacy radio navigation system. DME has a low channel utilization rate, leaving idle numerous resources that could be used by LDACS through the use of Dynamic Spectrum Access (DSA) in Cognitive Radio (CR). In order to avoid interferences and collisions while taking advantage of these idle resources, this thesis proposes a new LDACS Machine Learning (ML)-based Medium Access Control (MAC). It incorporates a Long Short Term Memory (LSTM) Recurrent Neural Network (RNN) in order to observe, learn, predict and avoid the DME licensed users. The results from this new MAC are analyzed and compared to two alternative approaches, showing the advantages of a ML-based approach.Publicationtype: Master Thesis107 304 - Some of the metrics are blocked by yourconsent settings
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Item type:Publication, Access status: with files , Reliable data streams in the presence of external interference(2018); Wireless mesh networks, as a tool for the wireless communication in large industrial applications, gained more and more popularity over the last few years. Thereby, these applications introduce new demands on the wireless solutions regarding their reliability and predictability in the presence of external interference, especially in the controlling and monitoring of safety critical systems. Additionally, many applications require a loss-free data transmission, in the sense that every packet sent at the application layer will eventually arrive at the receiver. This can mainly be achieved by retransmitting packets until they are successfully delivered and lowering the throughput of the application, so that no packet loss occurs due to queue drops. In the course of this thesis, two popular protocols for the application in wireless mesh networks and industrial applications are examined regarding their performance in the presence of external interference, namely Bluetooth Low Energy and IEEE 802.15.4 DSME. For these, a theoretical model is developed, which allows the calculation of the maximum transmission rate of an application in a multi-hop environment, so that a loss-free transmission is guaranteed. Furthermore, the model is evaluated with respect to different metrics and parameters and a comparison of the performance of the two protocols in the presence of external interference is provided. As a second contribution, a series of hardware experiments with and without artificially generated interference is conducted to assess the influence of interference under realistic conditions. The results are compared to the model and show good conformance. Finally, two mechanisms on top of the Bluetooth Low Energy application layer are introduced that significantly increase its reliability and performance in the presence of external interference.Publicationtype: Master Thesis388 721 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Forwarding strategies for 6LoWPAN-fragmented IPv6 datagramsThis dissertation explores different implementation strategies for the fragment-forwarding aspect of the 6LoWPAN protocol for “low power and lossy networks” (LLNs). The performance in terms of latency and reliability for the LLN-typical collection traffic pattern is analyzed for several “direct” and “reassembling” strategies. A novel approach based on snooping and suspending transmissions is developed and it is shown that this approach improves the end-to-reliability significantly in most of the evaluated simulation and testbed scenarios.Publicationtype: Doctoral Thesis768 2167 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Joint analysis of TDMA and geographic routing for a large scale wireless mesh network(2015-07-01); Wireless Mesh Networks are a promising technique for large scale networks with low-power and high reliability requirements such as in industrial plants. The shared transmission medium requires a medium access control mechanism which reduces the amount of parallel transmission, because nearby simultaneous transmitting devices hinder the successful reception at the destination device. The common CSMA-CA mechanism cannot satisfy the reliability requirement of an industrial plant, as many messages get dropped when the channel is busy for too long. Current standards introduce TDMA schemes for wireless mesh networks to improve the reliability with higher throughput and deterministic latency. In this work these standards are reviewed and one of the specified TDMA protocols, the deterministic synchronous multi-channel extension (DSME), is analyzed in more detail by examining its performance analytically and also by simulation. For this purpose, a simulation model was implemented, which is used to simulate an example network utilizing DSME and a promising geographic routing algorithm for a solar tower power plant. The introduced analytical model allows to determine the maximum performance for a network using DSME. The simulation results show that DSME achieves a strongly improved packet loss probability compared to CSMA-CA.Publicationtype: Master Thesis262 428