Drive-by-Wi-Fi: Model-Based Control Over Wireless at 1 kHz

In this work, we address the problem of remotely controlling possibly unstable systems using wireless channels with communication and control rates on the order of 1 kHz. While remote control over wireless has been used for applications in the kHz control rate range via low-bitrate communication protocols such as IEEE 802.15.4 (Zigbee) and IEEE 802.15.1 (Bluetooth), this represents the first successful demonstration of remotely controlling an unstable system, namely a balancing robot, using the high-bitrate IEEE 802.11 standard (Wi-Fi) with a control/communication rate in the kHz range, thus being suitable for time-critical industrial applications. This is achieved through a suitable design of both the communication and the control layer; the Wi-Fi protocol parameters are modified to reduce communication latency while still abiding to the standard and a model-based controller is implemented using a time-varying buffered Kalman filter to compensate for the sensor-to-controller lossy communication and using a packetized predictive controller to compensate for the controller-to-actuator lossy communication. The validity of this architecture is experimentally tested on a balancing robot, which adopts off-the-shelf embedded hardware (Rasperry Pi) and software (Arduino) within an industrial-like environment where substantial channel interference is present due to coexisting Wi-Fi networks, showing major improvements compared to more traditional emulation-based architectures.