Pjl Pieter Cuijpers

Hybrid process algebra

We develop an algebraic theory, called hybrid process algebra (HyPA), for the description and analysis of hybrid systems. HyPA is an extension of the process algebra ACP, with the disrupt operator from LOTOS and with flow clauses and re-initialization clauses for the description of continuous behavior and discontinuities. The semantics of HyPA is defined by means of deduction rules that associate a hybrid transition system with each process term. A large set of axioms is presented for a notion of bisimilarity. HyPA may be regarded as an algebraic approach to hybrid automata, although the specific semantics of re-initialization clauses makes HyPA a little more expressive.

Linearization of hybrid processes

HyPA is a formalism that is suitable for the algebraic analysis of hybrid systems, i.e., systems with continuous (physical) as well as discrete (computational) components. Linearization is a useful first step in this analysis, because it reduces the complexity of model descriptions by transforming them into so-called linear form. We present an algorithm for the linearization of hybrid processes modeled in a subset of hybrid process algebra (HyPA) and prove its correctness. This algorithm is able to linearize most HyPA constructs, except recursive parallelism, the empty process, and disrupts that are not a flow prefix. We also extend HyPA with an abstraction operator, which is used in the linearization algorithm.

Lost in Translation: Hybrid-Time Flows vs. Real-Time Transitions

Recently, hybrid-time flow systems have been introduced as an extension to timed transition systems, hybrid automata, continuous time evolutions of differential equations etc. Furthermore, a number of notions of bisimulation have been defined on these flow systems reflecting abstraction from certain timing properties. In this paper, we research the difference in abstraction level between this new semantic model of flow systems, and the more traditional model of real-time transition systems. We explore translations between the old and new semantic models, and we give a necessary and sufficient condition, called finite-set refutability, for these translations to be without loss of information. Finally, we show that differential inclusions with an upper-semicontinuous, closed and convex right-hand side, are finite-set refutable, and easily extend this result to impuls differential inclusions and hybrid automata.

A new data flow analysis model for TDM

This paper proposes a new data ow model for analyzing the worst-case temporal behavior of resource arbitration through Time Division Multiplexing (TDM). TDM arbitration allows resource sharing amongst the tasks of concurrent applications, where each application may have its own end-to-end hard real time requirements, such as minimum throughput and maximum latency. Current data flow modeling techniques for the temporal analysis of TDM arbitration over-estimate the worst-case temporal behavior of tasks. This causes unnecessary over-reservation of resources to the application, leading to under-utilization of system re- sources and unnecessary rejection of additional applications. We propose a conservative data ow model that accurately estimates the worst-case temporal behavior of TDM arbitration. Unlike existing models, we do not make restrictive assumptions on the characteristics of TDM, nor on the amount of resources reserved. This enables optimized resource allocation for TDM arbitration. We present a new model that closely mimicks the worst-case temporal behavior of TDM arbitration. We formally prove that this model is conservative with respect to the worst-case behavior of TDM arbitration, and we prove that it is strictly more accurate than the state-of-the-art. Quantitatively, we show that our new model leads to a 20% improvement of resource allocation, in a case study of a wireless LAN radio down-link.

Improving the performance of trickle-based data dissemination in low-power networks

Trickle is a polite gossip algorithm for managing communication traffic. It is of particular interest in low-power wireless networks for reducing the amount of control traffic, as in routing protocols (RPL), or reducing network congestion, as in multicast protocols (MPL). Trickle is used at the network or application level, and relies on up-to-date information on the activity of neighbors. This makes it vulnerable to interference from the media access control layer, which we explore in this paper. We present several scenarios how the MAC layer in low-power radios violates Trickle timing. As a case study, we analyze the impact of CSMA/CA with ContikiMAC on Trickle’s performance. Additionally, we propose a solution called Cleansing that resolves these issues.

A theory of desynchronisable closed loops system

The task of implementing a supervisory controller is non-trivial, even though different theories exist that allow automatic synthesis of these controllers in the form of automata. One of the reasons for this discord is due to the asynchronous interaction between a plant and its controller in implementations, whereas the existing supervisory control theories assume synchronous interaction. As a consequence the implementation suffer from the so-called inexact synchronisation problem. In this paper we address the issue of inexact synchronisation in a process algebraic setting, by solving a more general problem of refinement. We construct an asynchronous closed loop system by introducing a communication medium in a given synchronous closed loop system. Our goal is to find sufficient conditions under which a synchronous closed loop system is branching bisimilar to its corresponding asynchronous closed loop system.

A Context-Free Process as a Pushdown Automaton

A well-known theorem in automata theory states that every context-free language is accepted by a pushdown automaton. We investigate this theorem in the setting of processes, using the rooted branching bisimulation and contrasimulation equivalences instead of language equivalence. In process theory, different from automata theory, interaction is explicit, so we realize a pushdown automaton as a regular process communicating with a stack.

CASE STUDIES IN THE HYBRID PROCESS ALGEBRA HyPA

HyPA is an algebraic theory based on the classical process algebra Algebra of Communicating Processes (ACP) for the specification and analysis of hybrid systems. We have the idea that HyPA is also well suited for addressing various aspects of digital embedded systems including hardware, software and concurrency, as well as mixed-signal designs. To show that HyPA is useful for the specification and analysis of hybrid systems and that our idea is correct, we illustrate the use of HyPA with some case studies: a point-to-point communication , a thermostat, a positive-edge-triggered D flip flop, and a small part of a mixed-signal fuzzy controller.

Patching a patch — Software updates using horizontal patching

This paper presents a method for optimizing software updates of consumer electronic devices running multiple applications with a common software component, called horizontal patching. Instead of using separate deltas for patching different applications, the method generates one delta from the other. Due to the large similarities between the deltas, this horizontal delta is small in size. Experimental results on two test sets, consisting of software updates for sensor networks and smart phones, show that significant improvements can be achieved. Between 27% and 84% data can be saved from transmission, depending on the type of applications and shared components.

A process-theoretic look at automata

Automata theory presents roughly three types of automata: finite automata, pushdown automata and Turing machines. The automata are treated as language acceptors, and the expressiveness of the automata models are considered modulo language equivalence. This notion of equivalence is arguably too coarse to satisfactorily deal with a notion of interaction that is fundamental to contemporary computing. In this paper we therefore reconsider the automaton models from automata theory modulo branching bisimilarity, a well-known behavioral equivalence from process theory that has proved to be able to satisfactorily deal with interaction. We investigate to what extent some standard results from automata theory are still valid if branching bisimilarity is adopted as the preferred equivalence.