Publication type: Conferences

Traditional distributed embedded systems are configured using static environment information and thus do not support dynamic behavior of the system. The necessary flexibility in the system may be provided by the Flexible Time-Triggered (FTT) communication paradigm. If, in addition, it is required that the system operates continuously, the suitable fault tolerance mechanisms that provide high reliability have to be developed and deployed in the system. To be able to successfully assess those mechanisms, it is reasonable to develop simulation models that support injection of various types of faults.

This paper describes an OMNeT++ simulation model for distributed systems that are based on the Hard Real-Time Ethernet Switching (HaRTES) implementation of the FTT paradigm. The contribution of the paper is twofold. First, we provide a library of components that are required for modeling FTT networks with arbitrary number of FTT slaves connected to a HaRTES switch, and second, we used the developed components to build an FTT system that is suitable for assessing some of recently proposed mechanisms for tolerating certain transient faults in
the communication channel.

Despite the efforts devoted to increase the dependability of highly-reliable distributed fieldbus systems by means of simplex stars and replicated stars/buses, literature lacks of appropriate analyses that quantify the system reliability these topologies yield. In previous work, we proposed models to adequately quantify the system reliability benefits of simplex buses and simplex/replicated stars. However, a model for replicated buses is an open issue that needs to be addressed, as they normally include less components than stars and, thus, can be more reliable and cost-effective. To fill this gap, this paper presents a model that makes it possible to appropriately quantify the reliability that a highly-reliable distributed system can achieve when using a replicated bus.

The communication subsystem of distributed embedded systems (DES) that must operate continuously and satisfy unpredictable requirement changes must be reliable and flexible. Recently the Flexible Time-Triggered Replicated Star for Ethernet (FTTRS) has been proposed as a communication subsystem that satisfies these two attributes. It is based on the master/multi-slave Flexible-Time Triggered (FTT) communication paradigm and relies on two custom switches, each with its own embedded FTT master. Both masters are active simultaneously and provide the same service. Specifically, they simultaneously and periodically broadcast so-called trigger messages (TMs) in a redundant manner to make them robust to transient channel faults. One of the functions of these TMs is to divide the communication time into rounds called elementary cycles (ECs). For the correct operation of FTTRS, it is important that all slaves agree when each EC starts and ends. A mechanism to achieve this has been recently proposed. This paper presents a first implementation of this mechanism and a series of experimental tests that constitute a first step towards building a prototype of an FTTRS network.

Fault Tolerance for Flexible Time-Triggered Ethernet-based systems (FT4FTT) is a project to devise an architecture for distributed embedded systems that provides both flexibility to changing real-time requirements and high reliability through fault tolerance. One of the key parts of such an architecture is the communication subsystem. When designing such a subsystem many decisions have to be made. To understand how such decisions impact the reliability of the final design, in this paper we present a framework to evaluate the reliability of a large number of potential designs. The approach is based on storing a finite subset of the design space for the communication subsystem of FT4FTT in an undirected graph and then generating a continuous-time Markov chain from the graph to evaluate the reliability of each design belonging to the subset.

For a distributed embedded system (DES) to operate continuously in a dynamic environment, it must be flexible and highly reliable. This applies in particular to its communication subsystem. The Flexible Time-Triggered Replicated Star for Ethernet (FTTRS) aims at providing such a subsystem by means of a highly-reliable switched-Ethernet architecture based on the Flexible Time-Triggered paradigm (FTT), a master/slave communication paradigm where the master periodically polls the slaves using so-called trigger messages (TMs). In particular, FTTRS interconnects nodes by redundant communication paths provided by two switches, each embedding an FTT master that manages the communication. This allows FTTRS to tolerate the failure of one switch without interrupting the communication as long as the masters are replica determinate, i.e., provide identical service to the slaves. The master replica determinism entails the masters broadcasting their TMs in a lockstep fashion: when one master broadcasts a TM, the other should do the same quasi-simultaneously. In this paper we present a solution inspired by the Precision Time Protocol (PTP) for achieving this lockstep transmission and preliminary results showing the precision with which we can synchronize the masters on a software prototype.

We propose an appearance-based loop closure detection algorithm based on binary features and a Bag-of-Words scheme. Unlike other approaches that build the visual dictionary offline, we introduce an indexing method for binary features, which, in combination with an inverted index, enable us to obtain loop closure candidates in an online manner. These structures are used in a discrete Bayes filter to select final loop candidates and to ensure temporal coherency between predictions. Our approach is validated using two publicly available datasets of outdoor environments and compared with the state-of-the-art FAB-MAP algorithm, showing very promising results and demonstrating that binary features can be used for visual loop closure detection.

We propose an appearance-based approach for topological visual mapping and localization using local invariant features. To optimize running times, matchings between the current image and previously visited places are determined using an index based on a set of randomized kd-trees. We use a discrete Bayes filter for predicting loop candidates, whose observation model is a novel approach based on an efficient matching scheme between features. We assess our approach with several datasets obtained from indoor and outdoor environments under different weather conditions.

Effectiveness in loop closing detection is crucial to increase accuracy in SLAM (Simultaneous Localization and Mapping) for mobile robots. The most representative approaches to visual loop closing detection are based on feature matching or BOW (Bag of Words), being slow and needing a lot of memory resources or a previously defined vocabulary, which complicates and delays the whole process. This paper present a new visual LSH (Locality Sensitive Hashing)-based approach for loop closure detection, where images are hashed to accelerate considerably the whole comparison process. The algorithm is applied in AUV (Autonomous Underwater Vehicles), in several aquatic scenarios, showing promising results and the
validity of this proposal to be applied online.

A one-shot sensor for underwater 3D reconstruction is presented and tested underwater in a water tank. The system is composed of a RGB CCD camera and a 532 nm green laser with a Diffractive Optical Element attached to it. The laser projects a pattern of parallel lines into the scene. The deformed pattern obtained in the camera frame is then processed to obtain a non-dense 3D point cloud that can be later used for autonomous manipulation and grasping, or for detailed mapping of textureless objects or scenarios.