Performance Analysis of Wireless-enabled PROFIBUS Networks
Ref: HURRAY-TR-070607       Publication Date: 6, Jun, 2007

Performance Analysis of Wireless-enabled PROFIBUS Networks

Ref: HURRAY-TR-070607       Publication Date: 6, Jun, 2007

Most of the industrial community is very reluctant to integrate new technologies in their consolidated automation systems, either by preconception or by the lack of matureness of these technologies. When addressing communication systems for control applications, these fears become even more acute. Usually, these communication systems are based on fieldbus networks, which provide adequate levels of performance, dependability, timeliness and maintainability. The PROFIBUS (PROcess FIeldBUS) is the most widely used fieldbus, with over 15 million nodes worldwide, in applications ranging from discrete-part automation to process control.
During the cellular phone and WLAN boom of the last decade, soon it became evident that wireless (radio-based) communications could leverage a whole new set of potentialities in field level and control applications. Moving parts in machinery, hand-held equipment, wearable computers, transportation equipment and autonomous vehicles are just a few examples requiring wireless/mobile communications.
However, the requirements of real-time systems, usually served by fieldbuses, impose the use of predictable and reliable communication services, which provide certain guarantees on eventual delivery of packets and delivery times. Therefore, running real-time applications using wireless technology can be especially challenging, because the real-time and reliability requirements are more likely to be jeopardized than they would be over a wired channel.
The RFieldbus architecture, driven by the European Project IST-1999-11316 consortium has provided a complete solution where multiple segments and multiple wireless cells are interconnected via Physical Layer (PhL) Intermediate Systems (operating as repeaters). This solution is compatible with standard PROFIBUS, but the fact that all messages are broadcast throughout the network leads to some problems, namely no error containment between different segments and low responsiveness to failures. Additionally, it is also necessary to set the network parameters in a particular way which guarantees the operation of the network and leads to a lower performance.
These facts triggered the analysis and proposal of an alternative approach where the Intermediate Systems (ISs) operate at the Data Link Layer (DLL) level as bridges. This approach required two new protocols, one for supporting the communication between stations in different network segments – the Inter Domain Protocol (IDP), and another to support the mobility of wireless stations between different wireless segments – the Inter-Domain Mobility Procedure (IDMP).
The main objective of this dissertation is to compare the timing behaviour of the bridge and repeater-based approaches over error free and error prone environments. Additionally, we also intended to show that the bridge-based approach implementation is feasible and propose additional error detection and correction mechanisms which would improve its performance over error prone environments. To achieve these objectives two simulation tools have been developed, one for the repeater-based approach and another to the bridge-based approach, and a set of result analysis tools. Additionally, we have also developed another tool to simulate the mobility of wireless stations.

Paulo Baltarejo Sousa

Master Thesis, Instituto Superior Técnico.
Lisbon, Portugal.

Record Date: 6, Jun, 2007