On biases in precise point positioning with multi-constellation and multi-frequency GNSS data

© 2016 IOP Publishing Ltd. Various types of biases in Global Navigation Satellite System (GNSS) data preclude integer ambiguity fixing and degrade solution accuracy when not being corrected during precise point positioning (PPP). In this contribution, these biases are first reviewed, including satellite and receiver hardware biases, differential code biases, differential phase biases, initial fractional phase biases, inter-system receiver time biases, and system time scale offset. PPP models that take account of these biases are presented for two cases using ionosphere-free observations. The first case is when using primary signals that are used to generate precise orbits and clock corrections. The second case applies when using additional signals to the primary ones. In both cases, measurements from single and multiple constellations are addressed. It is suggested that the satellite-related code biases be handled as calibrated quantities that are obtained from multi-GNSS experiment products and the fractional phase cycle biases obtained from a network to allow for integer ambiguity fixing. Some receiver-related biases are removed using between-satellite single differencing, whereas other receiver biases such as inter-system biases are lumped with differential code and phase biases and need to be estimated. The testing results show that the treatment of biases significantly improves solution convergence in the float ambiguity PPP mode, and leads to ambiguity-fixed PPP within a few minutes with a small improvement in solution precision

Reliability Analysis of Component-Based Systems with Multiple Failure Modes

This paper presents a novel approach to the reliability modeling and analysis of a component-based system that allows dealing with multiple failure modes and studying the error propagation among components. The proposed model permits to specify the components attitude to produce, propagate, transform or mask different failure modes. These component-level reliability specifications together with information about systems global structure allow precise estimation of reliability properties by means of analytical closed formulas, probabilistic modelchecking or simulation methods. To support the rapid identification of components that could heavily affect systems reliability, we also show how our modeling approach easily support the automated estimation of the system sensitivity to variations in the reliability properties of its components. The results of this analysis allow system designers and developers to identify critical components where it is worth spending additional improvement efforts

ESCAPE: a component-based policy framework for sense and react applications.

Sense-and-react applications are characterised by the fact that actuators are able to react to data collected by sensors and change the monitored environment. With the introduction of nodes sporting actuators, Wireless Sensor Networks (WSNs) are being used for realising such applications. Sensor and actuator nodes are capable of interact locally. As a result, the logic that coordinates the activities of the different nodes towards a common goals has to be embedded in the network itself. In this scenario, the development of applications becomes more complex. In this paper, we present a component-based framework that facilitates the development of sense-and-react applications promoting reuse of code. While applications components are used to implement basic functionalities (sense and reaction) our framework allows the specification of application-domain requirements. Our framework is composed of a Publish/Subscribe Broker, a component-based service layer and a Policy Manager. The broker manages subscriptions information and the service layer provides mechanisms orthogonal to publish/subscribe core (e.g., diffusion protocols, data communication protocols, data encryption, etc.). The novelty of our approach is the introduction of the Policy Manager where policies are enforced. Policies are rules that govern the choices and behaviour of the system. They can be used for specifying which services have to be associated with the broker operations. Moreover, policies can embed rules for coordinating the activities of the different sensors and actuators for reaching the common goals of applications

An XML-Based Language to Support Performance and Reliability Modeling and Analysis in Software Architectures

Abstract. In recent years, the focus of software development has pro-gressively shifted upward, in the direction of the abstract level of ar-chitecture specification. However, while the functional properties of the systems have been extensively dealt with in the literature, relatively less attention has been given until recently to the specification and analysis at the architectural level of quality attributes such as performance and reliability. The contribution of this paper is twofold: first we discuss the type of information that should be provided at the architectural level in order to successfully address the problem of performance and reliability modeling and analysis of software systems; based on this discussion, we define an extension of the xADL architectural language that enables the support for stochastic modeling and analysis of performance and relia-bility in software architectures.

Titelei

Architectural description languages (ADLs) are used to specify a high-level, compositional view of a software application, specifying how a system is to be composed from coarse-grain components. ADLs usually come equipped with a formal dynamic semantics, facilitating specification and analysis of distributed and event-based systems. In this paper, we describe the Radl, an ADL framework that provides both a process and a structural view of web service-based systems. We use Petri-net descriptions to give a dynamic view of business workflow for web service collaboration. We adapt the approach of to define a form of design-by-contract for configuring workflow architectures. This serves as a configuration-level means of constructing safer, more robust systems

Software als Institution und ihre Gestaltbarkeit

Software regelt immer mehr zwischenmenschliche Interaktionen. Üblicherweise werden die Funktionsmechanismen, Wirkungen und Gestaltungsoptionen von Regeln in der Institutionenforschung behandelt. In diesem Artikel soll beleuchtet werden, inwieweit sich Ansätze der Institutionenforschung auf Software anwenden lassen und was sich aus dieser Forschungsperspektive zu den Regelungswirkungen und Gestaltungsoptionen von Software ableiten lässt