Data Rate Control for Closing Networked Control System Loop Over Costly Wireless Channel

Frederick M. Chache, Caden J. Pici, Ramesh Bharadwaj

Abstract: LoRa is a low power, long range modulation scheme that has grown in popularity in recent years. Wireless sensors utilizing LoRa have very limited bandwidth, particularly in regions like the EU, that impose strict 1% duty cycles. Thus, it is critical to reduce the number of transmissions while still meeting performance goals. In doing so, these sensors can greatly improve the quality of service and extend the battery life of the sensors. The importance of efficient bandwidth usage is amplified in time critical applications, such as in feedback control. In this work, we studied event-based transmission schemes used for sampling the state of a control system. Modern communication protocols, such as LoRa, have different transmission options to match transmission rates to channel quality. To model these transmission options, we extended past work by modeling the option to use different transmission schemes, which have independent packet drop rates and quantization error. To this end, we developed model based algorithms to allow nodes to adapt to unknown channel conditions when transmitting packets. We verified the performance of these algorithms in simulation and compared them to previous work.