A distributed networked approach for fault detection of large-scale systems

Networked systems present some key new challenges in the development of fault diagnosis architectures. This paper proposes a novel distributed networked fault detection methodology for large-scale interconnected systems. The proposed formulation incorporates a synchronization methodology with a filtering approach in order to reduce the effect of measurement noise and time delays on the fault detection performance. The proposed approach allows the monitoring of multi-rate systems, where asynchronous and delayed measurements are available. This is achieved through the development of a virtual sensor scheme with a model-based re-synchronization algorithm and a delay compensation strategy for distributed fault diagnostic units. The monitoring architecture exploits an adaptive approximator with learning capabilities for handling uncertainties in the interconnection dynamics. A consensus-based estimator with timevarying weights is introduced, for improving fault detectability in the case of variables shared among more than one subsystem. Furthermore, time-varying threshold functions are designed to prevent false-positive alarms. Analytical fault detectability sufficient conditions are derived and extensive simulation results are presented to illustrate the effectiveness of the distributed fault detection technique

System-on-chip Computing and Interconnection Architectures for Telecommunications and Signal Processing

This dissertation proposes novel architectures and design techniques targeting SoC building blocks for telecommunications and signal processing applications. Hardware implementation of Low-Density Parity-Check decoders is approached at both the algorithmic and the architecture level. Low-Density Parity-Check codes are a promising coding scheme for future communication standards due to their outstanding error correction performance. This work proposes a methodology for analyzing effects of finite precision arithmetic on error correction performance and hardware complexity. The methodology is throughout employed for co-designing the decoder. First, a low-complexity check node based on the P-output decoding principle is designed and characterized on a CMOS standard-cells library. Results demonstrate implementation loss below 0.2 dB down to BER of 10^{-8} and a saving in complexity up to 59% with respect to other works in recent literature. High-throughput and low-latency issues are addressed with modified single-phase decoding schedules. A new "memory-aware" schedule is proposed requiring down to 20% of memory with respect to the traditional two-phase flooding decoding. Additionally, throughput is doubled and logic complexity reduced of 12%. These advantages are traded-off with error correction performance, thus making the solution attractive only for long codes, as those adopted in the DVB-S2 standard. The "layered decoding" principle is extended to those codes not specifically conceived for this technique. Proposed architectures exhibit complexity savings in the order of 40% for both area and power consumption figures, while implementation loss is smaller than 0.05 dB. Most modern communication standards employ Orthogonal Frequency Division Multiplexing as part of their physical layer. The core of OFDM is the Fast Fourier Transform and its inverse in charge of symbols (de)modulation. Requirements on throughput and energy efficiency call for FFT hardware implementation, while ubiquity of FFT suggests the design of parametric, re-configurable and re-usable IP hardware macrocells. In this context, this thesis describes an FFT/IFFT core compiler particularly suited for implementation of OFDM communication systems. The tool employs an accuracy-driven configuration engine which automatically profiles the internal arithmetic and generates a core with minimum operands bit-width and thus minimum circuit complexity. The engine performs a closed-loop optimization over three different internal arithmetic models (fixed-point, block floating-point and convergent block floating-point) using the numerical accuracy budget given by the user as a reference point. The flexibility and re-usability of the proposed macrocell are illustrated through several case studies which encompass all current state-of-the-art OFDM communications standards (WLAN, WMAN, xDSL, DVB-T/H, DAB and UWB). Implementations results are presented for two deep sub-micron standard-cells libraries (65 and 90 nm) and commercially available FPGA devices. Compared with other FFT core compilers, the proposed environment produces macrocells with lower circuit complexity and same system level performance (throughput, transform size and numerical accuracy). The final part of this dissertation focuses on the Network-on-Chip design paradigm whose goal is building scalable communication infrastructures connecting hundreds of core. A low-complexity link architecture for mesochronous on-chip communication is discussed. The link enables skew constraint looseness in the clock tree synthesis, frequency speed-up, power consumption reduction and faster back-end turnarounds. The proposed architecture reaches a maximum clock frequency of 1 GHz on 65 nm low-leakage CMOS standard-cells library. In a complex test case with a full-blown NoC infrastructure, the link overhead is only 3% of chip area and 0.5% of leakage power consumption. Finally, a new methodology, named metacoding, is proposed. Metacoding generates correct-by-construction technology independent RTL codebases for NoC building blocks. The RTL coding phase is abstracted and modeled with an Object Oriented framework, integrated within a commercial tool for IP packaging (Synopsys CoreTools suite). Compared with traditional coding styles based on pre-processor directives, metacoding produces 65% smaller codebases and reduces the configurations to verify up to three orders of magnitude

Investigating Performance and Reliability of Process Bus Networks for Digital Protective Relaying

To reduce the cost of complex and long copper wiring, as well as to achieve flexibility in signal communications, IEC 61850 part 9-2 proposes a process bus communication network between process level switchyard equipments, and bay level protection and control (P&C) Intelligent Electronic Devices (IEDs). After successful implementation of Ethernet networks for IEC 61850 standard part 8-1 (station bus) at several substations worldwide, major manufacturers are currently working on the development of interoperable products for the IEC 61850-9-2 based process bus. The major technical challenges for applying Ethernet networks at process level include: 1) the performance of time critical messages for protection applications; 2) impacts of process bus Ethernet networks on the reliability of substation protection systems. This work starts with the performance analysis in terms of time critical Sampled Value (SV) messages loss and/or delay over the IEC 61850-9-2 process bus networks of a typical substation. Unlike GOOSE, the SV message is not repeated several times, and therefore, there is no assurance that each SV message will be received from the process bus network at protection IEDs. Therefore, the detailed modeling of IEC 61850 based substation protection devices, communication protocols, and packet format is carried out using an industry-trusted simulation tool OPNET, to study and quantify number of SV loss and delay over the process bus. The impact of SV loss/delay on digital substation protection systems is evident, and recognized by several manufacturers. Therefore, a sample value estimation algorithm is developed in order to enhance the performance of digital substation protection functions by estimating the lost and delayed sampled values. The error of estimation is evaluated in detail considering several scenarios of power system relaying. The work is further carried out to investigate the possible impact of SV loss/delay on protection functions, and test the proposed SV estimation algorithm using the hardware setup. Therefore, a state-of-the-art process bus laboratory with the protection IEDs and merging unit playback simulator using industrial computers on the QNX hard-real-time platform, is developed for a typical IEC 61850-9-2 based process bus network. Moreover, the proposed SV estimation algorithm is implemented as a part of bus differential and transmission line distance protection IEDs, and it is tested using the developed experimental setup for various SV loss/delay scenarios and power system fault conditions. In addition to the performance analysis, this work also focuses on the reliability aspects of protection systems with process bus communication network. To study the impact of process bus communication on reliability indices of a substation protection function, the detailed reliability modeling and analysis is carried out for a typical substation layout. First of all, reliability analysis is done using Reliability Block Diagrams (RBD) considering various practical process bus architectures, as well as, time synchronization techniques. After obtaining important failure rates from the RBD, an extended Markov model is proposed to analyze the reliability indices of protection systems, such as, protection unavailability, abnormal unavailability, and loss of security. It is shown with the proposed Markov model that the implementation of sampled value estimation improves the reliability indices of a protection system

Wireless Real-Time Communication in Tunnel-like Environments using Wireless Mesh Networks: The WICKPro Protocol

En los últimos años, las redes inalámbricas se están utilizando cada vez más en entornos industriales debido a sus ventajas respecto a redes cableadas: menor coste de instalación, soporte de movilidad, instalación en lugares donde los cables pueden ser problemáticos y mayor facilidad de reconfiguración. Estas redes inalámbricas normalmente deben proporcionar comunicación en tiempo real para satisfacer los requerimientos de las aplicaciones. Podemos encontrar ejemplos de comunicación en tiempo real con redes inalámbricas para entornos industriales en el campo de la automatización industrial y en el control de procesos, donde redes inalámbricas de radiofrecuencia han sido utilizadas para posibilitar comunicación en tiempo real con un despliegue sencillo. Asimismo, la industria también está interesada en comunicaciones en tiempo real en entornos subterráneos, puesto que existen diversas actividades que se llevan a cabo en escenarios tales como túneles y minas, incluyendo operaciones de minería, vigilancia, intervención y rescate. Las redes inalámbricas malladas (Wireless Mesh Networks, WMNs) representan una solución prometedora para conseguir comunicaci ón en tiempo real en entornos inalámbricos, dado que proporcionan una red troncal inalámbrica formada por encaminadores (routers) que es utilizada por terminales móviles. Sin embargo, las WMNs también presentan algunos retos: la naturaleza multisalto de estas redes causa interferencias entre flujos e interferencias de un flujo consigo mismo, además de que la propagación inalámbrica sufre shadowing y propagación multicamino. El estándar IEEE 802.11 ha sido ampliamente utilizado en redes WMNs debido a su bajo coste y la operación en bandas frecuenciales sin licencia. El problema es que su protocolo de acceso al medio (Medium Access Control, MAC) no es determinista y que sus comunicaciones sufren los problemas del terminal oculto y expuesto. Esta tesis doctoral se centra en el soporte de comunicaciones en tiempo real en entornos tipo túnel utilizando redes WMNs. Con este objetivo, desarrollamos un protocolo MAC y de nivel de red denominado WIreless Chain networK Protocol (WICKPro) que funciona sobre IEEE 802.11. Más concretamente, en este trabajo diseñamos dos versiones de este protocolo para proporcionar soporte de tráfico de tiempo real firme (Firm Real-Time, FRT) y de tiempo real no estricto (Soft Real-Time, SRT): FRT-WICKPro y SRT-WICKPro. Asimismo, proponemos un algoritmo de hand-off conocido como Double-Threshold Hand-off (DoTHa) para el manejo de la movilidad en SRT-WICKPro WICKPro utiliza un esquema de paso de testigo para solventar las interferencias entre flujos y de un flujo consigo mismo, así como los problemas del terminal oculto y expuesto, dado que este esquema no permite que dos nodos transmitan al mismo tiempo. Esta solución es razonable para redes pequeñas donde el re uso espacial es imposible o limitado. Para tratar la naturaleza no determinista de IEEE 802.11, combinamos el esquema de paso de testigo con una planificación cíclica global. Como es habitual en planificación cíclica, el hiperperiodo es dividido en un conjunto de ciclos secundarios. FRT-WICKPro inicia el paso de testigo de forma síncrona para satisfacer estrictamente dichos ciclos secundarios, mientras que SRT-WICKPro implementa un paso de testigo asíncrono y permite sobrepasar los ciclos secundarios, por lo que desacopla los ciclos secundarios reales de los te_oricos. Finalmente, DoTHa lidia con el shadowing y la propagación multicamino. Para abordar el shadowing, DoTHa permite llevar a cabo el proceso de hand-off en la región conectada y en la región de transición de un enlace, mientras que la propagación multicamino es ignorada para el proceso de hand-off porque la potencia recibida es promediada. Nuestras propuestas fueron validadas en experimentos de laboratorio y de campo, así como en simulación. Como un estudio de caso, llevamos a cabo la teleoperación de un robot móvil en dos entornos confinados: los pasillos de un edificio y el túnel del Somport. El túnel del Somport es un antiguo túnel ferroviario fuera de servicio que conecta España y Francia por los Pirineos Centrales. Aunque los robots autónomos son cada vez más importantes, la tecnología no está suficientemente madura para manejar entornos con alto dinamismo como sistemas de fabricación reconfigurables, o para realizar decisiones de vida o muerte, por ejemplo después de un desastre con contaminación radiactiva. Las aplicaciones que pueden beneficiarse de la teleoperación de robots móviles incluyen la monitorización en tiempo real y el uso de maquinaria robotizada, por ejemplo camiones dumper y máquinas tuneladoras, que podrían ser operadas remotamente para evitar poner en peligro vidas humanas.Industrial applications have been shifting towards wireless networks in recent years because they present several advantages compared with their wired counterparts: lower deployment cost, mobility support, installation in places where cables may be problematic, and easier reconfiguration. These industrial wireless networks usually must provide real-time communication to meet application requirements. Examples of wireless real-time communication for industrial applications can be found in factory automation and process control, where Radio Frequency wireless communication technologies have been employed to support flexible real-time communication with simple deployment. Likewise, industry is also interested in real-time communication in underground environments, since there are several activities that are carried out in scenarios such as tunnels and mines, including mining, surveillance, intervention, and rescue operations. Wireless Mesh Networks (WMNs) are promising enablers to achieve wireless real-time communication because they provide a wireless backbone comprised by dedicated routers that is utilized by mobile terminals. However, WMNs also present several challenges: wireless multi-hopping causes inter-flow and intra-flow interferences, and wireless propagation suffers shadowing and multi-path fading. The IEEE 802.11 standard has been widely used in WMNs due to its low cost and the operation in unlicensed frequency bands. The downside is that its Medium Access Control (MAC) protocol is non-deterministic, and that its communications suffer from the hidden and exposed terminal problems. This PhD thesis focuses on real-time communication in tunnel-like environments by using WMNs. Particularly, we develop a MAC and network protocol on top of the IEEE 802.11 standard to provide real-time capabilities, so-called WIreless Chain networK Protocol (WICKPro). Two WICKPro versions are designed to provide Firm Real-Time (FRT) or Soft Real-Time (SRT) traffic support: FRT-WICKPro and SRT-WICKPro. We also propose a hand-off algorithm dubbed Double-Threshold Hand-off (DoTHa) to manage mobility in SRT-WICKPro. WICKPro employs a token-passing scheme to solve the inter-flow and intra-flow interferences as well as the hidden and exposed terminal problems, since this scheme does not allow two nodes to transmit at the same time. This is a reasonable solution for small-scale networks where spatial reuse is impossible or limited. The non-deterministic nature of IEEE 802.11 is faced by combining the token-passing mechanism with a polling approach based on a global cyclic packet schedule. As usual in cyclic scheduling, the hyper-period is divided into minor cycles. FRT-WICKPro triggers the token synchronously and fulfills strictly minor cycles, whereas SRT-WICKPro carries out asynchronous token-passing and lets minor cycles be overrun, thereby decoupling the theoretic and the actual minor cycles. Finally, DoTHa deals with shadowing and multi-path fading. Shadowing is addressed by providing the opportunity of triggering hand-off in the connected and transitional regions of a link, while multi-path fading is neglected for hand-off purposes by smoothing the received signal power. We tested our proposals in laboratory and field experiments, as well as in simulation. As a case study, we carried out the tele-operation of a mobile robot within two confined environments: the corridors of a building and the Somport tunnel. The Somport tunnel is an old out-of-service railway tunnel that connects Spain and France through the Central Pyrenees. Although autonomous robots are becoming more and more important, technology is not mature enough to manage highly dynamic environments such as reconfigurable manufacturing systems, or to make life-and-death decisions, e.g., after a disaster with radioactivity contamination. Applications that can benefit from mobile robot tele-operation include real-time monitoring and the use of robotized machinery, for example, dumper trucks and tunneling machines, which could be remotely operated to avoid endangering human lives

DeSyRe: on-Demand System Reliability

The DeSyRe project builds on-demand adaptive and reliable Systems-on-Chips (SoCs). As fabrication technology scales down, chips are becoming less reliable, thereby incurring increased power and performance costs for fault tolerance. To make matters worse, power density is becoming a significant limiting factor in SoC design, in general. In the face of such changes in the technological landscape, current solutions for fault tolerance are expected to introduce excessive overheads in future systems. Moreover, attempting to design and manufacture a totally defect and fault-free system, would impact heavily, even prohibitively, the design, manufacturing, and testing costs, as well as the system performance and power consumption. In this context, DeSyRe delivers a new generation of systems that are reliable by design at well-balanced power, performance, and design costs. In our attempt to reduce the overheads of fault-tolerance, only a small fraction of the chip is built to be fault-free. This fault-free part is then employed to manage the remaining fault-prone resources of the SoC. The DeSyRe framework is applied to two medical systems with high safety requirements (measured using the IEC 61508 functional safety standard) and tight power and performance constraints