Reliability (Engineering)

To ensure that a system is robust and will continue operation even when facing
disruptive or traumatic events, we have created a methodology for system architects and
designers which may be used to locate risks and hazards in a design and enable the
development of more robust and resilient system architectures. It uncovers design
vulnerabilities by conducting a complete exploration of a systems’ component
operational state space by observing the system from multi-dimensional perspectives and
conducts a quantitative design space analysis by means of probabilistic risk assessment
using Bayesian Networks. Furthermore, we developed a tool which automated this
methodology and demonstrated its use in an assessment of the OCTT PHM communication system architecture. To boost the robustness of a wireless communication system and efficiently allocate bandwidth, manage throughput, and ensure quality of service on a wireless link, we created a wireless link management architecture which applies sensor fusion to gather and store platform networked sensor metrics, uses time series forecasting to predict the platform position, and manages data transmission for the links (class based, packet scheduling and capacity allocation). To validate our architecture, we developed a link management tool capable of forecasting the link quality and uses cross-layer scheduling and allocation to modify capacity allocation at the IP layer for various packet flows (HTTP, SSH, RTP) and prevent congestion and priority inversion. Wireless sensor networks (WSN) are vulnerable to a plethora of different fault types and external attacks after their deployment. To maintain trust in these systems and
increase WSN reliability in various scenarios, we developed a framework for node fault
detection and prediction in WSNs. Individual wireless sensor nodes sense characteristics
of an object or environment. After a smart device successfully connects to a WSN’s base
station, these sensed metrics are gathered, sent to and stored on the device from each
node in the network, in real time. The framework issues alerts identifying nodes which
are classified as faulty and when specific sensors exceed a percentage of a threshold
(normal range), it is capable of discerning between faulty sensor hardware and anomalous
sensed conditions. Furthermore we developed two proof of concept, prototype
applications based on this framework.

Reliability and risk assessment play an important role in product design, development and production. In mass production items, data is abundant and testing in product development and certification is usually thorough. In contrast, for nonparametric applications, product cost is high, there is limited production and the product is often used only once and discarded. In this type of manufacturing, data is usually limited because of the cost of testing. This makes reliability and risk assessments a difficult task. To circumvent this shortfall in data and its analysis, it is the intent of this paper to provide an alternative approach to models for reliability and risk analysis. This was accomplished by first surveying existing literature and models; then, approaching the problem with a set of block diagrams for each of the required analyses. Additionally, a full set of current models and failure analysis tools were also incorporated. With these tools the proposed methodology was demonstrated in case studies. These studies provided the validation for the methodology presented.

Reliability is a key system characteristic that is an increasing concern for current systems. Greater reliability is necessary due to the new ways in which services are delivered to the public. Services are used by many industries, including health care, government, telecommunications, tools, and products. We have defined an approach to incorporate reliability along the stages of system development. We first did a survey of existing dependability patterns to evaluate their possible use in this methodology. We have defined a systematic methodology that helps the designer apply reliability in all steps of the development life cycle in the form of patterns. A systematic failure enumeration process to define corresponding countermeasures was proposed as a guideline to define where reliability is needed. We introduced the idea of failure patterns which show how failures manifest and propagate in a system. We also looked at how to combine reliability and security. Finally, we defined an approach to certify the level of reliability of an implemented web service. All these steps lead towards a complete methodology.

The efforts addressed in this thesis refer to assaying the degradations in modern solar cells used in space-borne and/or nuclear environment applications. This study is motivated to address the following: 1. Modeling degradations in Si pn-junction solar cells (devices-under-test or DUTs) under different ionizing radiation dosages 2. Preemptive and predictive testing to determine the aforesaid degradations that decide eventual reliability of the DUTs; and 3. Using electrical overstressing (EOS) to emulate the fluence of ionizing radiation dosage on the DUT. Relevant analytical methods, computational efforts and experimental studies are described. Forward/reverse characteristics as well as ac impedance performance of a set of DUTs under pre- and post- electrical overstressings are evaluated. Change in observed DUT characteristics are correlated to equivalent ionizing-radiation dosages. The results are compiled and cause-effect considerations are discussed. Conclusions are enumerated and inferences are made with direction for future studies.

The need to achieve dependability in critical infrastructures has become indispensable for government and commercial enterprises. This need has become more necessary with the proliferation of malicious attacks on critical systems, such as healthcare, aerospace and airline applications. Additionally, due to the widespread use of web services in critical systems, the need to ensure their reliability is paramount. We believe that patterns can be used to achieve dependability. We conducted a survey of fault tolerance, reliability and web service products and patterns to better understand them. One objective of our survey is to evaluate the state of these patterns, and to investigate which standards are being used in products and their tool support. Our survey found that these patterns are insufficient, and many web services products do not use them. In light of this, we wrote some fault tolerance and web services reliability patterns and present an analysis of them.