Behavioural hybrid process calculus

Process algebra is a theoretical framework for the modelling and analysis of the behaviour of concurrent discrete event systems that has been developed within computer science in past quarter century. It has generated a deeper nderstanding of the nature of concepts such as observable behaviour in the presence of nondeterminism, system composition by interconnection of concurrent component systems, and notions of behavioural equivalence of such systems. It has contributed fundamental concepts such as bisimulation, and has been successfully used in a wide range of problems and practical applications in concurrent systems. We believe that the basic tenets of process algebra are highly compatible with the behavioural approach to dynamical systems. In our contribution we present an extension of classical process algebra that is suitable for the modelling and analysis of continuous and hybrid dynamical systems. It provides a natural framework for the concurrent composition of such systems, and can deal with nondeterministic behaviour that may arise from the occurrence of internal switching events. Standard process algebraic techniques lead to the characterisation of the observable behaviour of such systems as equivalence classes under some suitably adapted notion of bisimulation

Stability Analysis for Hybrid Automata Using Conservative Gains

This paper presents a stability analysis approach for a class of hybrid\ud automata. It is assumed that the dynamics in each location of the hybrid automaton is linear and asymptotically stable, and that the guards on the transitions are hyperplanes in the state space. For each pair of ingoing and outgoing transitions in a location a conservative estimate is made of the gain via a Lyapunov function for the dynamics in that location. It is shown how the choice of the Lyapunov function can be optimized to obtain the best possible estimate. The calculated conservative gains are used in defining a so-called gain automaton that forms the basis of an algorithmic criterion for the stability of the hybrid automaton

Specification and verification of radiation therapy system with respiratory compensation using Uppaal

The goal of radiation therapy is to give as much dose as possible to the target volume of tissue and avoid giving any dose to a healthy tissue. Advances of the digital control allow performing accurate plans and treatments. Unfortunately, motion compensation during the treatment remains a considerable problem. Currently, a combination of the different techniques, such as gating (restricting movement of patient) and periodic emission are used to avoid damaging healthy tissue. This paper focuses on systems that completely compensate respiratory movement (up to certain limit) and start by investigating adequacy of the existing hardware and software platform. In this paper a radiation therapy system consisting of a HexaPOD couch with 6-degrees movement, a tracking camera, a marker (markers) and a controller is modeled. A formal un-timed model was evaluated and found to be insufficient to completely determine adequacy of the system to compensate respiratory motion. Therefore, un-timed model was extended to include time and investigated. It provides more information than un-timed model, but does not answer all interesting question. Therefore, based on the results further research directions are sketched

A WSN approach to unmanned aerial surveillance of traffic anomalies: Some challenges and potential solutions

Stationary CCTV cameras are often used to help monitor car movements and detect any anomalies - e.g., accidents, cars going faster than the allowed speed, driving under the influence of alcohol, etc. The height of the cameras can limit their effectiveness and the types of image processing algorithm which can be used. With advancements in the development of inexpensive aerial flying objects and wireless devices, these two technologies can be coupled to support enhanced surveillance. The flying objects can carry multiple cameras and be sent well above the ground to capture and feed video/image information back to a ground station. In addition, because of the height the objects can achieve, they can capture videos and images which could lend themselves more suitably for the application of a variety of video and image processing algorithms to assist analysts in detecting any anomalies. In this paper, we examine some main challenges of using flying objects for surveillance purposes and propose some potential solutions to these challenges. By doing so, we attempt to provide the basis for developing a framework to build a viable system for improved surveillance based on low-cost equipment. © 2013 IEEE.t.published_or_final_versio

Hybrid Techniques for Hybrid Systems

Computer controlled systems are almost omnipresent nowadays. We expect such systems to function properly at any time we need them. The malfunctioning of home electronics just irritates us, but glitches in a car, power plant or medical support system may threaten life, and faults in nuclear missile control facility may bring the end to civilisation. Such ubiquity of computer-based control puts very high reliability requirements on such systems. Hybrid systems combine continuous real-time behaviour and discrete events. Research in hybrid systems aims at providing means for reliable design and production of hybrid systems. In this thesis, we explore the world of hybrid systems. We acknowledge relevance and complexity of hybrid systems research, and emphasise several different research topics: modelling, analysis, testing and deployment of hybrid systems. We illustrate hybrid systems by presenting a collection of examples that reflect hybrid phenomena, its variety and occurrence in different applications. Of course, the list is not exhaustive, because only illustrative examples were chosen. However, it represents the diversity of hybrid systems sufficiently well to reveal the size and complexity of problems, and the broadness of the application area. We survey several major formalisms for modelling and analysis of hybrid systems. We overview an existing classification of hybrid systems, and propose a generalised classification scheme for diverse frameworks. Moreover, we classify the surveyed formalisms according to the proposed scheme. We propose a technique for stability estimation for a certain class of hybrid automata. It combines ideas from computer science and control theory, and is based on cycles detection and conservative gains estimation. We borrow the well-known algorithm for transforming a finite automaton into an equivalent regular expression for cycles detection from computer science. From control theory, we take the idea of conservative gains and use them to estimate stability of cycles. We introduce Behavioural Hybrid Process Calculus (BHPC), a formalism for modelling and analysis of hybrid systems. It combines process algebraic techniques and the behavioural approach [Polderman and Willems, 1998] to dynamical systems. We take an attempt to advance fusion of computer science and control theory in hybrid systems research. BHPC is based on two fundamental notions of actions and trajectories that describe discrete and continuous evolution of dynamical systems, respectively. At a higher abstraction level these two types of behaviour are treated uniformly, i.e., as normal elements of process algebra. Their behaviour is defined using structural operational semantics (SOS) rules [Plotkin, 1981, 2003]. Moreover, the rules already respect the differences between trajectory prefixes and action prefixes, based on our intuition on how such processes should behave. For example, in parallel composition trajectory prefixes are always required to synchronise, while for action prefixes interleaving semantics is adopted. Furthermore, we define a hybrid strong bisimulation relation for BHPC and prove that it is congruence. It is one of the most important properties to attain well-defined compositionality. Such a property allows interchanging bisimilar processes in any process algebraic expression. In other words, it allows refining process, changing their internal representation, and interchanging them without any losses as long as they manifest the same behaviour. We propose a technique for simulation of BHPC. We devise a simulation algorithm for a subset of BHPC operators and test some of the proposed techniques in the BHAVE prototype. The proposed simulation algorithm defines one of the possible ways to simulate Behavioural Hybrid Process Calculus. Moreover, we survey the major problems in simulation of hybrid systems in the light of BHPC and in a more general layout. For some of the issues we propose solutions, for the remaining we discuss potential ways to tackle the problems

Modeling and analysis of radiation therapy system with respiratory compensation using Uppaal

The goal of radiation therapy is to give as much dose as possible to the exact target location and minimizing any dose to a normal tissue. Advances of Cyber-physical control systems allow planning and provide very accurate treatments. However, the current technology does not sufficiently compensate a respiratory movement that is especially important in case of lung (area) cancer. In this paper we present a model of radiation treatment system developed to analyze a system that compensates respiratory motion. We use Uppaal, an integrated tool environment for modeling, validation and verification of real-time systems modeled as networks of timed automata, extended with data types (bounded integers, arrays, etc.)