Graceful Degradation

Control systems for electrical microgrids rely ever more on an information infrastructure, consisting of heterogeneous off-the-shelf communication technology for hardware, software and networking. This provides flexibility for the application as new services become possible, but also implies vulnerabilities as the correct execution of microgrid control algorithms can be hampered by the incorrect functioning of the information infrastructure, as a result of accidental and malicious faults. In order to provide resilient microgrid control, the info'structure needs to be fault-tolerant and able to deal with a dynamic environment; overlay networks can provide the required graceful degradation in case of unrecovered failures, rather than resulting in a complete breakdown.

Anti-Lock Braking Systems (ABS) and Brake-by-Wire Systems (BBW) are safety-critical applications by nature. Such systems are required to demonstrate high degrees of dependability. Fault-tolerance is the primary means to achieve dependability at runtime and has been an active research area for decades. Fault-tolerance is usually achieved in in traditional embedded computing systems through redundancy and voting methods. In such systems hardware units, actuators, sensors, and communication networks are replicated were special voters vote against faulty units. In addition to traditional hardware and software redundancy, hybrid and reconfiguration-based approaches to fault-tolerance are evolving. In this paper, we present a reconfiguration-based fault-tolerant approach to achieve high dependability in ABS BBW braking systems. The proposed architecture makes use of other components of less safety-critical systems to maintain high dependability in the more safety-critical systems. This is achieved by migrating safety-critical software tasks from embedded computer hardware that runs into a malfunction to other embedded computing hardware running less-critical software tasks. Or by using a different configuration in terms of the used speed sensors and type of ABS. The proposed architecture is on average 20% more reliable than conventional ABS architectures assuming equal reliabilities of different components.

The ubiquity and simplicity of HTTP makes it a popular choice for Web-based video retrieval. However, HTTP was not designed for re-trieving data with just-in-time tolerances; HTTP servers have always taken an as-fast-as-possible approach to data delivery. For media ...

Four principal features of autonomous control systems are left both unaddressed and unaddressable by present-day engineering methodologies: 1. The ability to operate effectively in environments that are only partially known beforehand at design time; 2. A level of generality that allows a system to re-assess and re-define the fulfillment of its mission in light of unexpected constraints or other unforeseen changes in the environment; 3. The ability to operate effectively in environments of significant complexity; and 4. The ability to degrade gracefully – how it can continue striving to achieve its main goals when resources become scarce, or in light of other expected or unexpected constraining factors that impede its progress. We describe new methodological and engineering principles for addressing these shortcomings, that we have used to design a machine that becomes increasingly better at behaving in underspecified circumstances, in a goal-directed way, on the job, by modeling itself and its environment as experience accumulates. Based on principles of autocatalysis, endogeny, and reflectivity, the work provides an architectural blueprint for constructing systems with high levels of operational autonomy in underspecified circumstances, starting from only a small amount of designer-specified code – a seed. Using a value- driven dynamic priority scheduling to control the parallel execution of a vast number of lines of reasoning, the system accumulates increasingly useful models of its experience, resulting in recursive self-improvement that can be autonomously sustained after the machine leaves the lab, within the boundaries imposed by its designers. A prototype system has been implemented and demonstrated to learn a complex real-world task – real-time multimodal dialogue with humans – by on-line observation. Our work presents solutions to several challenges that must be solved for achieving artificial general intelligence.

This paper describes a novel architecture of fault tolerant solid state mass memory (SSMM) for satellite applications. Mass memories with low-latency time, high throughput, and storage capabilities cannot be easily implemented using space qualified components, due to the inevitable technological delay of these kind of components. For this reason, the choice of commercial off the shelf (COTS) components is mandatory for this application. Therefore, the design of an electronic system for space applications, based on commercial components, must match the reliability requirements using system level methodologies. In the proposed architecture, error-correcting codes are used to strengthen the commercial dynamic random access memory (DRAM) chips, while the system controller is developed by applying fault tolerant design solutions. The main features of the SSMM are the dynamic reconfiguration capability, and the high performances which can be gracefully reduced in case of permanent faults, maintaining part of the system functionality. The paper shows the system design methodology, the architecture, and the simulation results of the SSMM. The properties of the building blocks are described in detail both in their functionality and fault tolerant capabilities. A detailed analysis of the system reliability and data integrity is reported. The graceful degradation capability of our system allows different levels of acceptable performances, in terms of active I/O link interfaces and storage capability. The results also show that the overall reliability of the SSMM is almost the same using different RS coding schemes, allowing a dynamic reconfiguration of the coding to reduce the latency (shorter codewords), or to improve the data integrity (longer codewords). The use of a scrubbing technique can be useful if a high SEU rate is expected, or if the data must be stored for a long period in the SSMM. The reported simulations show the behavior of the SSMM in presence of permanent and transient faults. In fact, we show that the SCU is able to recover from transient faults. On the other hand, using a spare microcontroller also hard faults can be tolerated. The distributed file system confines the unrecoverable fault effects only in a single I/O Interface. In this way, the SSMM m- aintains its capability to store and read data. The proposed system allows obtaining SSMM characterized by high reliability and high speed due the intrinsic parallelism of the switching matrix.

The bitstream structure of layered media formats such as Scalable Video Coding (SVC) or Multiview Video Coding (MVC) opens up new opportunities for their distribution in Mobile TV services. Features like graceful degradation or the support of the 3D experience in a backwards-compatible way are enabled. Reason is that parts of the media stream are more important than others with each part itself providing a useful media representation. Typically, the decoding of some parts of the bitstream is only possible, if the corresponding more important parts are correctly received. Hence, unequal error protection (UEP) can be applied protecting important parts of the bitstream more strongly than others. Mobile broadcast systems typically apply forward error correction (FEC) on upper layers to cope with transmission errors, which the physical layer FEC cannot correct. Today's FEC solutions are optimized to transmit single layer video. The exploitation of the dependencies in layered media codecs for UEP using FEC is the subject of this paper. The presented scheme, which is called layer-aware FEC (LA-FEC), incorporates the dependencies of the layered video codec into the FEC code construction. A combinatorial analysis is derived to show the potential theoretical gain in terms of FEC decoding probability and video quality. Furthermore, the implementation of LA-FEC as an extension of the Raptor FEC and the related signaling are described. The performance of layer-aware Raptor code with SVC is shown by experimental results in a DVB-H environment showing significant improvements achieved by LA-FEC.