Networked Control Systems with Intermittent Acknowledgement

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Networked control systems (NCSs) utilize communication channels or networks to transmit signals among different components. A crucial issue in NCSs is that data transmission is no longer lossless, and data packets may be dropped due to various reasons. Two well-known transport protocols, Transmission Control Protocol (TCP) and User Datagram Protocol (UDP), are usually used to treat this issue. NCSs with TCP and UDP deployed are called TCP-like and UDP-like NCSs, respectively. TCP-like NCSs feature the reliable data transmission by sending an acknowledgement (ACK) of receipt from destination to source but require extra resources to establish and maintain a connection between source and destination. Also, handshake, retransmission, and other mechanisms may cause a significant delay in the feedback loop. By contrast, UDP-like NCSs, at the cost of lower data delivery reliability, reduce resource consumption and cause lower latency. However, the performance deterioration resulting from data loss may be unacceptable for some control tasks. Despite the remarkable progress in TCP-like and UDP-like NCSs, emerging control-related applications such as wireless process automation, autonomous driving, and networked factory have posed new challenges. On the one hand, high data reliability and control performance are desired as many packets are related to the safety-critical message, whose loss and resulting performance deterioration can be harmful to people or equipment. On the other hand, low latency is essential to fulfiling stringent timeliness and agility requirements of control tasks. Besides, reduced resource consumption is desired as many devices are powered by batteries and have limited resources for computation, control, and communication. Neither TCP-like NCSs nor UDP-like NCSs is able to address all these issues, and this calls for new approaches and tools. To this end, a new type of NCSs with intermittent ACK (iACK-NCSs), and related control analysis and design framework covering modelling, estimation, control, and distributed deployment are to be developed in this research program. The novelty of iACK-NCSs is that a pair of source and destination generates ACK signals adaptively according to control targets, plant dynamics, and network conditions. Through deliberate integration of active and adaptive ACK, it has the potential to achieve fast responses, low latency, and high-performance estimation/control with minimum use of resources. The successful completion of the research program will not only deepen understanding of theory on control and communication in the context of networked and distributed systems but also provide novel algorithms and protocols which can be applied to practical networked control problems. Also, it will lead to the training of research students in a significant and rapidly growing area, enabling them to develop new approaches and skills which are very likely to impact both academic and industrial sectors.