Resource Allocation in Distributed Control and Embedded Systems

Traditionally, control design problems are decoupled from software design and implementation considerations. Such a separation allowed the control and computer science communities to focus on specific problems independently, and led to the development that we are familiar with nowadays. However, as explained in Arzen et al. [13], this separation relies on the fact that these two fields use very simplified models of their interface with each other. In fact, control designers disregard the characteristics of the implementation and the available computational and communication resources. On the other hand, real-time designers see the control loop as a periodic task with a hard deadline, that have sometimes to fulfill data dependency constraints (especially when the sensing and actuation are distant). Recently, researchers from these two communities have shown that if more elaborate models are used, significant improvements in terms of implementation efficiency and quality of control may be achieved. This integrative co-design approach is central to this book.This chapter is organized into two parts. The first part presents the state of the art of the real-time scheduling theory, focusing on the most used results in distributed control and embedded system (DCES) applications. We start by presenting real-time single-processor scheduling problems. Next, we focus on the problem of ensuring real-time networked communications. We emphasize different methods for managing the access concurrency having a determinant impact on the guarantee of deterministic real-time communications. Finally, an overview of the problem of guaranteeing end-to-end real-time constraints in distributed systems is given. In the second part, we present a state of the art of the new approaches, that are based on more elaborate models, and that take into account both the dynamic nature of the controlled systems as well as some characteristics of their implementation. Various problems and models were discussed in the literature. We propose a classification of these different approaches and illustrate the different problems and models that were addressed.