Tuning of IEEE 802.11 MAC for improving real-time in industrial wireless networks

The problem of enhancing reliability while providing real-time guarantees in industrial communication over wireless networks has been widely addressed by the scientific literature. Several analyses have been carried out that consider this problem in a real-time scheduling framework, modeling both real-time transmission flows and possible retransmissions as a set of periodic tasks. These analyses, however, approach the schedulability problem from a high level point of view, where lower communication layers are modeled as if they were a unique stack that introduces a certain error probability and do not take into account their actual behavior. In this paper, we present an accurate evaluation of the transmission times of the packets belonging to the flows in case of an IEEE 802.11g WLAN is employed at the lower layers. Moreover, we address the negative influence of the wireless network non-deterministic behavior, mainly caused by both backoff procedures and MAC-layer retransmissions, on the feasibility of a flow set providing some possible solutions.