Drive-by-Wi-Fi: Testing 1 kHz control experiments over wireless

Wireless communication is a very appealing technology for industrial automation and networked control systems but much more unreliable as compared to wired solutions. Existing wireless standards for industrial automation such as ISA100 and WirelessHart address such unreliability but are limited to low control rates not exceeding 20 Hz, which are suitable for supervisory tasks, but not for high-bandwidth applications. In this work, we propose to use Wi-Fi, which thanks to its high data rates (> 300 Mbit/s), seems to be eligible for high performance applications requiring control rates greater than 1 kHz. Preliminary works mostly rely on emulation approaches, in which no change in the control design is needed, but the communication protocols have to be modified to enforce determinism (e.g. via TDMA-like protocols) at the price of longer delays. Conversely, this work follows a different paradigm, where the unreliability of the communication, due to random packet losses and delays, is coped by a robust model-based controller, which is capable of dealing with the stochastic nature of the communication channel while guaranteeing high control rates. The proposed approach has been tested on a hardware-in-the-loop laboratory setup involving conventional off-the-shelf Wi-Fi network interface cards, which showed how control rates in the order of 1 kHz are well within the possibility of Wi-Fi, even in the presence of substantial communication channel noise.