Isochronous Wireless Network for Real-time Communication in Industrial Automation
In industrial automation systems the deployment of wireless technologies is more and more common. This is mainly due to applications which consist either of moving components, for example rotating machine parts, or require a high degree of flexibility. However, due to their high real-time requirements the implementation of applications, such as wireless networked control systems (NCS), is rather limited or even impossible with existing wireless technologies. The objective of this dissertation is to design an isochronous wireless network for industrial control applications with guaranteed latencies and jitter. The main challenges are a non-deterministic medium access of existing systems, the uncontrolled, shared wireless medium and its limited capacity, as well as the asynchronous behaviour of wireless and wired communication systems degrading the temporal behaviour of such hybrid systems. Based on the requirements analysis of real industrial applications and the characterisation of the wireless channel for the application scenario, a solution approach is presented consisting of a deterministic, TDMA-based medium access control, a dynamic resource allocation and the provision of a global time base for the wired and the wireless network. The global time base allows a seamless and synchronous integration into existing wired Real-time Ethernet systems. An implementation prototype of the proposed wireless system and a simulation case study are used for the evaluation of the solution approach in two case studies. The prototype is used for the evaluation in a real factory environment and for the validation of the simulation model. Due to given scalability constraints of the prototype, a second case study based on a realistic simulation model is conducted. A realistic channel model for the simulation, implemented based on the channel characterisation, allows more realistic simulation results. The obtained evaluation results show that latencies ≤ 10 ms and a maximum jitter ≤ 100 μs can be achieved with the presented solution approach as long as all components are active. Thus the solution approach allows a deployment within NCSs with the given requirements. As soon as components are deactivated, the behaviour of the network is significantly degraded and the requirements cannot be satisfied any more.