Section: New Results

Communication and control co-design for networked systems

Energy-aware communication and control co-design in wireless networked control systems

Participants : C. Canudas de Wit [Contact person] , N. Cardoso de Castro, F. Garin.

This work is the topic of the PhD thesis of N. Cardoso de Castro. We have considered an event-based approach to energy-efficient management of the radio chip in the sensor node of a wireless networked control system [54] , [66] . Indeed, as we had pointed out in the review paper [67] , the radio is the main energy consumer, and intermittent data transmission allows one to reduce the use of the radio. While the existing literature in the control community on event-based control only addresses policies using two radio-modes (Transmitting/Sleep), our work follows some considerations on the radio-chip modes well-known in the communication networks literature, and introduces some intermediate radio-modes, which consume more energy than `Sleep’ but allow to reach the transmitting mode consuming less energy in the transition. We propose an event-based radio-mode switching policy, which allows to perform a trade-off between energy saving and performance of the control application. To this end, a switched model describes the system, taking into account control and communication. The optimal switching policy is computed using Dynamic Programming. This work is described in [66] and in a journal paper (in preparation). A further research direction is the exploration of receding-horizon techniques (Model Predictive Control), to solve a slightly modified formulation of the same problem. This research is in collaboration with Dr. Daniel Quevedo, senior lecturer at the University of Newcastle, Australia, in particular during a three-months visit of N. Cardoso de Castro at University of Newcastle.

Adaptive Delta Modulation in Networked Controlled Systems with bounded disturbances

Participants : C. Canudas de Wit [Contact person] , F. Gomez-Estern [University of Sevilla] , F. R. Rubio [University of Sevilla] .

In the context of communication and control co-design for networked systems, this work investigates the closed-loop properties of the differential coding scheme known as Delta Modulation when used in feedback loops within the context of linear systems controlled through a communication network [19] . We propose a new adaptive scheme with variable quantization step, by defining an adaptation law exclusively in terms of information available at both the transmitter and receiver. With this approach, global asymptotic stability of the networked control system is achieved for a class of controllable (possibly unstable) linear plants. Moreover, thanks to the globally defined switching policy, this architecture enjoys a disturbance rejection property that allows the system to recover from any finite–time unbounded disturbance or communication loss.

Control, communication, computation (3C) co-design: Multi - level classification and formulation

Participants : C. Canudas de Wit [Contact person] , A. Farhadi [University of Melbourne] .

We introduce here an integration framework for Control/Communication/Computation (3C) co-design based on the motivating example of fleet control of Autonomous Underwater Vehicles (AUVs) [35] , [75] . Specifically, we address the problem of almost sure stability of an unstable system with multiple observations over packet erasure channel, with emphasis on coding computational complexity. We look at the tradeoff between duty cycle for feedback channel use, coding computational complexity, and performance. We compare coding computational complexity and performance for two cases: a) No feedback channel at all, and b) Feedback channel all the time. It is shown that the strategy of using feedback channel results in a better performance.