Challenges and recent advances in the design of real-time wireless Cyber-Physical Systems

Cyber-Physical Systems (CPS) refer to systems where some intelligence is embedded into devices that interact with their environment. Using wireless technology in such systems is desirable for better flexibility, improved maintainability, and cost reduction, among others. Moreover, CPS applications often specify deadlines; that is, maximal tolerable delays between the execution of distributed tasks. Systems that guarantee to meet such deadlines are called real-time systems. In the past few years, a technique known as synchronous transmissions (ST) has been shown to enable reliable and energy efficient communication, which is promising for the design of real-time wireless CPS.

We identify at least three issues that limit the adoption of ST in this domain: (i) ST is difficult to use due to stringent time synchronization requirements (in the order of $\mu \text{s}$). There is a lack of tools to facilitate the implementation of ST by CPS engineers, which are often not wireless communication experts. (ii) There are only few examples showcasing the use of ST for CPS applications and academic works based on ST tend to focus on communication rather than applications. Convincing proof-of-concept CPS applications are missing. (iii) The inherent variability of the wireless environment makes performance evaluation challenging. The lack of an agreed-upon methodology hinders experiment reproducibility and limits the confidence in the performance claims. This paper synthesizes recent advances what address these three problems, thereby enabling significant progress for future applications of low-power wireless technology in real-time CPS.