A fixed-priority access scheme for industrial Wi-Fi networks

The current version of IEEE 802.11, based on EDCA, is unable to support fine-grained assignments of priorities to messages. Instead, such an ability could be advantageous in distributed real-time control systems communicating over the air, as it would enable the exploitation of feasibility analysis to assess whether or not timing constraints are met. In this paper, a proposal is made for implementing a simple fixed-priority access scheme on conventional, commercial Wi-Fi devices. Basically, this is obtained by disabling the random backoff mechanism and suitably managing interframe gaps only. In particular, each real-time message is assigned a unique gap duration, so as to help in preventing collisions. An experimental campaign has been carried out on real devices aimed at assessing the performance this approach can achieve.