Reliable Data Streams in the Presence of External Interference
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.