Influence of real components behavior on the performance of wireless industrial communication systems

The performance analysis of wireless industrial communication systems could be significantly improved by introducing adequate models of the employed real components obtained through experimental measurements. In this paper we present an example of characterization of the elaboration delay introduced by a commercial access point. The pdfs of such a delay, obtained under different traffic conditions, show that the considered device enters a sort of sleep mode if it remains inactive for a period longer than a measured threshold. Resuming the access point from this sleep state makes the delay it introduces higher and more variable. The aforementioned delay pdfs are used to analyze via numerical simulations the behavior of a hybrid (wired/wireless) industrial network using a master-slave protocol. We consider as a performance indicator, the jitter on the cyclic queries of the slaves, relevant to two different polling strategies, namely continuous and TDMA-based polling. The simulation results show that the jitter introduced by the access point behavior is relevant. On the other hand, the TDMA-based technique allows to mitigate such negative effects provided that the TDMA slots assigned to the slaves are chosen carefully.