Adaptive Network-Device Cooperative Diversity for Ultra-Reliable and Low-Latency Wireless Control

Wireless motion control in the next generation of industrial control systems aims to provide the sensor/actuator devices on a factory floor with continuous closed-loop control updates from the controller entity, requiring communications with extremely low latency in the order of sub-ms and "cablelike" high reliability. This paper introduces a wireless communication protocol that uses channel state information (CSI) and cooperative communication among the devices to best utilize the radio resources and provide an ultra-reliable radio access. We propose to use CSI to identify devices with strong and weak channel conditions. We show that strong devices in the network are best to be served in a single-hop transmission with transmission rate adapted to their instantaneous channel conditions. Meanwhile, the remainder of time-frequency resources is used to serve the devices with weak channel condition, using a two-hop transmission with cooperative relaying. We formulate the optimization problem of partitioning time budget between the two groups and associating devices to each group. Numerical solution to the optimization problem and simulation results are provided. Thanks to combining multi-user diversity gain together with cooperative relaying, the proposed solution provides orders of magnitude improvement in system reliability, resulting in more than 10 dB signal to noise ratio (SNR) gain at 10−5 system outage probability point, with respect to state-of-the-art protocols.