Verónica Vasconcelos

Tolerating transient communication faults with online traffic scheduling

Building distributed embedded systems that will be fault-free for all their lifetime is virtually impossible, thus the systems must deal with them if a continued correct behavior is needed. This is the case of safety-critical systems, such as X-by-wire systems in the automotive domain. Concerning transient communication faults in particular, they can be dealt with at various levels of the protocol stacks, with different techniques, e.g., temporal and spatial redundancy. In this paper we focus on temporal redundancy and we address the limitations imposed by typical time-triggered systems, commonly found in safety-critical systems, arising from their static traffic definition. In these systems the use of temporal redundancy to handle communication errors requires the pre-allocation of communication resources that, in the absence of errors, are wasted. Therefore, we propose an online traffic scheduling approach in which retransmissions are consistently scheduled with the remaining time-triggered traffic, using the unique flexibility provided by the FTT-CAN protocol (Flexible Time-Triggered communication on CAN). We address the integration of appropriate fault detectors in the FTT-CAN protocol to monitor the bus activity and re-schedule omitted messages. We show that this approach is more efficient than the static allocations, since communication resources are only allocated when necessary. We also discuss alternative realizations and validate the approach with initial results from a prototype implementation.

Efficient transient error recovery in FlexRay using the dynamic segment

In safety-critical systems a global high-reliability is sought, including in the communication network when a distributed control system is used. The FlexRay protocol was developed within the automotive industry with the necessary characteristics to respond to the demands of safety-critical applications, e.g. X-by-wire. Nevertheless, the FlexRay protocol does not define a mechanism to guarantee message delivery, nor defines global error signaling, leaving the resolution of these problems to the application. This paper presents a preliminary proposal for a mechanism that uses temporal redundancy to recover transient errors in time-triggered messages. An extra node is used to trigger message retransmissions whenever errors or omissions do effectively occur. This mechanism uses the FlexRay dynamic segment to implement message retransmissions, leading to a minimum recovery time, typically one cycle, together with a very small bandwidth usage.

Error recovery in time-triggered communication systems using servers

In communication systems, transient faults will eventually occur. Thus, some mechanism is necessary to handle them and achieve appropriate levels of reliability, particularly in safety-critical systems. One possibility is to rely on temporal redundancy, i.e., using message retransmissions. General requirements for such a mechanism would include a parsimonious use of extra bandwidth while guaranteeing the schedulability of the message set. In this paper we propose using on-line traffic scheduling together with scheduling servers to recover message errors in time-triggered systems on Controller Area Network (CAN), taking advantage of the Flexible Time-Triggered CAN protocol. This novel mechanism is shown to offer a desired error recovery latency using much less extra bandwidth than typical approaches used in time-triggered systems. In this paper we present this novel error recovery mechanism, including a thorough characterization as well as configuration guidelines, namely concerning how to choose the server parameters (type, period and capacity). The correctness of the proposed approach and its superior performance are validated with simulation using several communication benchmarks available in the literature.

Landmarks detection to assist the navigation of visually impaired people

Assistive technology enables people to achieve independence in the accomplishment of their daily tasks and enhance their quality of life. Visual information is the basis for most navigational tasks, so visually impaired individuals are at disadvantage due to the lack of information or given insufficient information about their surrounding environment. With the recent advances in inclusive technology it is possible to extend the support given to people with visual disabilities during their mobility. In this context we propose a new algorithm to recognize landmarks suitably placed on sidewalks. The proposed algorithm uses a combination of Peano-Hilbert Space Filling Curves for dimension reduction of image data and Ensemble Empirical Mode Decomposition (EEMD) to pre-process the image, resulting on a fast and efficient recognition method and revealing a promising solution.

Comparing scheduling policies for a message transient error recovery server in a time-triggered setting

Distributed systems rely in communication networks, typically a bus, in order to exchange messages and fulfill their goals. However, message transmission is subject to interferences that ultimately can lead to message corruption. In systems where a high-reliability is sought, error recovery mechanisms can be deployed in order to give the required reliability level, and this can be done in the spatial or temporal domain. In the scope of the FTT paradigm, and applied to the FTT-CAN protocol, the authors have previously presented a time domain recovery method using message retransmissions controlled by a server. In this article we assess the impact of different scheduling policies for the server, presenting a qualitative evaluation of the alternatives, complemented by a simulation study, in order to verify their advantages and weak points.

Enhanced Classification of Interstitial Lung Disease Patterns in HRCT Images Using Differential Lacunarity

The analysis and interpretation of high-resolution computed tomography (HRCT) images of the chest in the presence of interstitial lung disease (ILD) is a time-consuming task which requires experience. In this paper, a computer-aided diagnosis (CAD) scheme is proposed to assist radiologists in the differentiation of lung patterns associated with ILD and healthy lung parenchyma. Regions of interest were described by a set of texture attributes extracted using differential lacunarity (DLac) and classical methods of statistical texture analysis. The proposed strategy to compute DLac allowed a multiscale texture analysis, while maintaining sensitivity to small details. Support Vector Machines were employed to distinguish between lung patterns. Training and model selection were performed over a stratified 10-fold cross-validation (CV). Dimensional reduction was made based on stepwise regression (F-test, p value < 0.01) during CV. An accuracy of 95.8 ± 2.2% in the differentiation of normal lung pattern from ILD patterns and an overall accuracy of 94.5 ± 2.1% in a multiclass scenario revealed the potential of the proposed CAD in clinical practice. Experimental results showed that the performance of the CAD was improved by combining multiscale DLac with classical statistical texture analysis.

Error Recovery in the Time-Triggered Paradigm with FTT-CAN

Data networks are naturally prone to interferences that can corrupt messages, leading to performance degradation or even to critical failure of the corresponding distributed system. To improve resilience of critical systems, time-triggered networks are frequently used, based on communication schedules defined at design-time. These networks offer prompt error detection, but slow error recovery that can only be compensated with bandwidth overprovisioning. On the contrary, the Flexible Time-Triggered (FTT) paradigm uses online traffic scheduling, which enables a compromise between error detection and recovery that can achieve timely recovery with a fraction of the needed bandwidth. This article presents a new method to recover transmission errors in a time-triggered Controller Area Network (CAN) network, based on the Flexible Time-Triggered paradigm, namely FTT-CAN. The method is based on using a server (traffic shaper) to regulate the retransmission of corrupted or omitted messages. We show how to design the server to simultaneously: (1) meet a predefined reliability goal, when considering worst case error recovery scenarios bounded probabilistically by a Poisson process that models the fault arrival rate; and, (2) limit the direct and indirect interference in the message set, preserving overall system schedulability. Extensive simulations with multiple scenarios, based on practical and randomly generated systems, show a reduction of two orders of magnitude in the average bandwidth taken by the proposed error recovery mechanism, when compared with traditional approaches available in the literature based on adding extra pre-defined transmission slots.

Executive function assessment in Parkinson's disease patients using mobile devices

The objective of the project presented in this paper is to stimulate and evaluate the executive function in Parkinsons patients. This project is being developed in partnership with the Coimbra Hospital and Universitary Centre and the private social solidarity institution CASPAE. It aims to answer specific needs identified in the neurology service during the medical appointments. A common test to assess executive function is the Trail Making Test (TMT). This test is done on paper during the medical appointments for the diagnosis and follow-up of patients with the executive function diminished, such as Parkinsons disease patients. The way the TMT is done poses some problems that led to the development of an application for smartphones and tablets, with Android OS. This application has two operating modes: “Appointment”, and “Train”. The “Appointment Mode” makes the realization, reading, and the organization of the tests results easier. The “Train Mode” allows that patients improve their executive function performing tests that are randomly generated on your own smartphone.

Schedulability analysis of server-based error-recovery mechanisms for time-triggered systems

Distributed Embedded Systems are subject to transient communication faults that need being detected and mitigated in safety-critical scopes. This paper addresses error recovery in time-triggered systems based on the Controller Area Network (CAN). It extends a recent work that proposed using online traffic scheduling, combined with servers, to implement dynamic message retransmissions. In particular, we provide a schedulability analysis that considers the interference of the error-recovery server in the time-triggered traffic, as well as a methodology to compute the worst-case response time of messages affected by errors. We also present a comparison with related error-recovery methods that confirms the superiority of the proposed method.

Study Lung Tool: A Way to Understand HRTC Lung Parenchyma

The purpose of the described system is to aid radiologists on their daily routine in the task of analyzing HRCT lung images and to contribute to a more accurate and fast diagnosis. We developed a framework -Study Lung Toolwith the objective of gather information from radiologists, in a systematic way. Using Study Lung Tool framework, the radiologist analyzes HRCT scans, outlines regions of typical pattern and characterizes the patterns. A database of typical patterns associated with common pulmonary diseases was created. The information gathered can be a valuable teaching tool to every one that intends to understand HRCT lung parenchyma. The proposed system discriminates between normal and abnormal patterns of lung parenchyma based on statistical texture analysis extracted from HRCT lung scans. An overall accuracy of 89,2%, a sensitivity of 92,7% and a specificity of 83,6% were achieved.