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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SENTIENT (SCHEDULING OF EVENT-TRIGGERED CONTROL TASKS)

Teaser

Summary

The advances in electronic communication and computation have enabled the ubiquity of Cyber-Physical Systems (CPS): digital systems that regulate and control all sorts of physical processes, such as chemical reactors, water distribution and power networks. These systems require the timely communication of sensor measurements and control actions to provide their prescribed functionalities. Event-triggered control (ETC) techniques, which communicate only when needed to enforce performance, have attracted attention as a mean to reduce the communication traffic and save energy on (wireless) networked control systems (NCS). However, despite ETCâ€™s great communication reductions, the scheduling of the aperiodic (and largely unpredictable) traffic that ETC generates remains widely unaddressed â€“ hindering its true potential for energy and bandwidth savings.

To address this problem, in the project SENTIENT we are investigation the following scientific challenges:

- the construction of models for ETCâ€™s communication traffic;
- the design of schedulers based on such models guaranteeing prescribed performance levels.

These challenges are addressed employing methods at the cross-roads between theoretical computer science, control systems and communications engineering.
In particular, we are following a two step approach:

1. modeling as timed-priced-game-automata (TPGA) the timing of communications of event-triggered control systems;
2. solving games over TPGAs to prevent data communication collisions and ensure prescribed performances for the control tasks.

The project\'s most practical outcome are algorithms (and their software implementations) facilitating the efficient implementation of control loops over shared communication resources, and increasing the energy efficiency of wireless NCS.
The advances will be demonstrated on automotive and wireless water-distribution control applications, showcasing the potential economic impact from the reduction of implementation and maintenance costs on CPSs.

Work performed

1. A change of paradigm when constructing the traffic abstractions has been proposed and developed: instead of partitioning the space and then compute the associated times, reversing the logic and partitioning first time and then compute the associated state-space regions help mitigate in part the curse of dimensionality. This approach is reflected on a publication at Necsys 2018 and two journal submissions (one for linear systems and the other for non-linear systems)
2. The construction of abstractions considering the presence of disturbances has been addressed for linear systems in two forms reflected on the conference paper in Necsys 2018 (with an extension submitted to a journal), and on a published paper at the IEEE Transactions on Automatic Control.
3. The work on abstractions for non-linear systems has led to the discovery of some theoretical problems in the paper of Anta, Tabuada (TAC 2011) which served as basis for our research plan. These issues have been solved and a more effective computational approach to construct isochronous manifolds has been proposed. These advances have been submitted for a journal publication with an application to self-triggered control (STC).
4. Some small progress on distributed abstractions has been made to enable our first experiments on wireless control of water distribution systems. These experiments have been performed on a Hardware-in-the-loop setup in collaboration with the University of Trento, illustrating how a low-power wireless communication protocol can be used to implement event-triggered controllers. A journal publication is being prepared.
5. Progress in creating a toolchain for scheduling: a tool has been constructed allowing to bring the abstractions of event-triggered controllersâ€™ traffic to UPPAAL for their analysis and to synthesize schedulers.
6. A test-bed for the testing of wireless control in the context of water distribution is being instrumented with a network of wireless sensors and actuators to start real experiments.

Final results

The expected advances will go beyond the state of the art in several directions:

1. providing models of traffic of ETC systems, which are largely unavailable at this moment.
2. allowing a more methodological evaluation of ETC systems and their expected communication reductions, through automatic analysis of the constructed models
3. enabling the (automated) synthesis of schedulers for ETC systems in a modular way

These advances, together with their implementations as software packages will greatly simplify the design and analysis of event-based systems, and in turn of more efficient Cyber-Physical Systems in which networking is central.