Polling-based MAC protocols for improving real-time performance in a wireless PROFIBUS

The idea of having a wireless PROFIBUS is appealing, since this can bring benefits like reduced cabling need and mobile stations to the factory floor. But unfortunately wireless transmission is error-prone, which affects the timeliness and reliability behavior users expect from a fieldbus system (hard real-time). In this paper we compare two different approaches for the medium access control and link layer of a wireless PROFIBUS system with respect to their so-called real-time performance in the presence of transmission errors. Specifically, we compare the existing PROFIBUS MAC and link layer protocol with a simple round-robin protocol. It shows up that round-robin delivers significantly better real-time performance than the PROFIBUS protocol under bursty error conditions. In a second step we propose three add-ons to round-robin and we show that they further increase the real-time performance of round-robin. The add-ons take certain characteristics of the wireless medium into account. Keywords—PROFIBUS, Wireless PROFIBUS, Real-Time Performance, MAC Protocols, Polling