Energy efficient scheduling for cluster-tree wireless sensor networks with time-bounded data flows: application to IEEE 802.15.4/ZigBee

Cluster scheduling and collision avoidance are crucial issues in large-scale cluster-tree Wireless Sensor Networks (WSNs). The paper presents a methodology that provides a Time Division Cluster Scheduling (TDCS) mechanism based on the cyclic extension of RCPS/TC (Resource Constrained Project Scheduling with Temporal Constraints) problem for a cluster-tree WSN, assuming bounded communication errors. The objective is to meet all end-to-end deadlines of a predefined set of time-bounded data flows while minimizing the energy consumption of the nodes by setting the TDCS period as long as possible. Sinceeach cluster is active only once during the period, the end-to-end delay of a given flow may span over several periods when there are the flows with opposite direction. The scheduling tool enables system designers to efficiently configure all required parameters of the IEEE 802.15.4/ZigBee beaconenabled cluster-tree WSNs in the network design time. The performance evaluation of thescheduling tool shows that the problems with dozens of nodes can be solved while using optimal solvers

Balancing the Waiting Times in a Simple Traffic Intersection Model

We propose a novel dynamical model of a simple traffic intersection, where the state variables represent the queue lengths and the mean waiting times in the queues. Including the mean waiting times in the model allows for a more fair traffic control, where the waiting times of the individual vehicles in the various streets of the intersection are taken into account to some degree. The model is linearized and its parameters are estimated using real traffic data measured during one day in Prague. For the balancing of the waiting times, two different controllers are considered: a linear quadratic regulator and a nonlinear model predictive controller. The controllers are evaluated in simulations where real traffic data is used for the incoming flows

Continuous Petri Nets and Polytopes

This article addresses the problem of the computation of instantaneous firing speed in Invariant Behavior state (IB-state) of Constant speed Continuous Petri Net (CCPN) with presence of actual conflicts. The adopted approach is based on polyhedral computations applied to specify an area of possible instantaneous firing speed. If the actual conflicts are resolved by global priorities, the instantaneous firing speed is found in a set of the polytop vertices or alternatively it is found by one formulation of the linear programming problem per each priority level. The approach shown in this article assumes the speed maximisation being prior to priority resolution

Petri Net Models for Manufacturing Systems

This paper presents an experimental laboratory setup aimed at creating a flexible manufacturing system for use in teaching real-time control. The machine models (robots, conveyors, etc.) are self-contained elements with their own intelligence, communicating with a master computer. A supervisor program running on the master computer is implemented by a real-time operating system, enabling the dynamic creation of processes. The supervisor program is fully parameterized, with parameters specifying manufacturing subtasks of all machines and synchronization among them. This makes the control system modular and flexible. A manufacturing task is specified by Petri nets that are automatically decomposed into a set of unique P-invariant generators. The choice of concurrent processes corresponding to P-invariants is done semi-automatically to reflect the physical tenor of the manufacturing system