David J. Holding

Radio range adjustment for energy efficient wireless sensor networks

In wireless ad hoc sensor networks, energy use is in many cases the most important constraint since it corresponds directly to operational lifetime. Topology management schemes such as GAF put the redundant nodes for routing to sleep in order to save the energy. The radio range will affect the number of neighbouring nodes, which collaborate to forward data to a base station or sink. In this paper we study a simple linear network and deduce the relationship between optimal radio range and traffic. We find that half of the power can be saved if the radio range is adjusted appropriately compared with the best case where equal radio ranges are used.

Design of reliable software in distributed systems using the conversation scheme

The problems of error detection and recovery are examined in a number of concurrent processes expressed as a set of communicating sequential processes (CSP). A method is proposed which uses a Petri net model to formally identify both the state and the state reachability tree of a distributed system. These are used to define systematically the boundaries of a conversation, including the recovery and test lines which are essential parts of the fault-tolerant mechanism. The techniques are implemented using the OCCAM programming language, which is derived from CSP. The application of this method is shown by a control example.

Analysis of energy conservation in sensor networks

In this paper we use the Erlang theory to quantitatively analyse the trade offs between energy conservation and quality of service in an ad-hoc wireless sensor network. Nodes can be either sleeping, where no transmission or reception can occur, or awake where traffic is processed. Increasing the proportion of time spent in the sleeping state will decrease throughput and increase packet loss and delivery delay. However there is a complex relationship between sleeping time and energy consumption. Increasing the sleeping time does not always lead to an increase in the energy saved. We identify the energy consumption profile for various levels of sensor network activity and derive an optimum energy saving curve that provides a basis for the design of extended-life ad hoc wireless sensor networks.

UML and Petri nets for design and analysis of distributed systems

This paper presents a modification to UML to improve the modelling and analysis of discrete-event dynamic system (DEDS) representations of manufacturing systems. It shows how Petri nets can be used to improve the representation and analysis of the dynamic model of a system specified using UML. Finally the technique is illustrated by its application to a simplified production line.

The specification and design of hard real-time systems using timed and temporal petri nets

Abstract This paper considers the specification and design of software for embedded real-time systems which have safety functions or implications for safety. It addresses the problem of specifying a system in a tangible application-oriented manner while retaining sufficient formalism and rigour for exploring and verifying the performance and safety properties of the system. It presents an overview of relevant formal specification techniques and examines the use of temporal and timed Petri nets in specification, verification and performance evaluation. These techniques are applied to the design of the real-time control software for two independently-driven interacting mechanisms for a high-speed packaging machine.

Routing analysis and energy efficiency in wireless sensor networks

A simple energy model of radio transceivers with analysis of ad-hoc routing to optimize system performance is combined in this paper. A simple example of a linear wireless ad hoc sensor network is used to deduce the relationship between traffic load and optimal radio range of topology management schemes. It is found that half of the power can be saved if the radio range is adjusted appropriately compared with the best case where equal radio ranges are used.

A comparison of temporal Petri net techniques in the specification and design of hard real-time systems

Abstract This paper assesses the suitability of two techniques, based on Petri nets and temporal logic, for the specification, design and verification of a real-time industrial control system that forms part of a high speed packaging machine. It presents a brief overview of Petri nets and temporal logic and describes how the strengths of both techniques are captured in the combined formalism of temporal Petri nets. The paper discusses the advantages of using temporal Petri nets and an extended form of temporal Petri nets in specification and design. These techniques are applied to the specification and design of control and synchronisation logic for a flexible manufacturing system comprising loosely coupled asynchronous mechanisms. It is shown that the problem can be specified elegantly using Petri nets, the verification of the specification can be completely carried out using temporal logic, and the specification can be evolved into a design in such a manner that the design inherits the specified properties.

Design of Distributed Manufacturing Systems using UML and Petri Nets

Abstract This paper describes the design of a supervisory control system for a distributed manufacturing process, which forms part of a wider manufacturing system. The focus of the paper is on the design of a verifiable discrete event controller using a UML based method. The approach adopted involves (i) using Petri net models instead of conventional Statecharts to provide analytic Dynamic Models; and (ii) using compositional Petri net techniques to synthesise the Interconnection Model. The model of the complete controller can be then analysed and verified using Petri net theory. The approach is demonstrated by application to a prototype packaging machine.

The Formalisation and Analysis of Sequential Function Charts Using a Petri Net Approach

Abstract This paper presents an analysis of the sequential function charts (SFC), defined in the international standard IEC 1131 Part 3. It examines the relationship between the evaluation system and the execution system of SFC and its action qualifiers, to show that inaccuracies exist in SFC. It presents a formalisation of SFC using an extended time-related Petri net which permits the analysis of SFC designs. The method is illustrated by a simple application.

The design and simulation of software fault tolerant mechanisms for application in distributed processing systems

Abstract A number of fault tolerant mechanisms have been proposed for sequential and concurrent systems. Discussion of these mechanisms has concentrated on structural aspects; a systematic approach to the design and placement of fault tolerant structures has been lacking. This paper considers techniques for the systematic and proper placement of software fault tolerant structures for distributed systems. It describes the design of such a system and shows how the error detection and recovery mechanisms can be included in the system model. The methods which are presented should have a wide range of application including microprocessor and transputer implementation.