Publication type: Conferences

This paper reports on a novel technique to visually detect loop closings in feature-poor underwater environments in order to increase the accuracy of vision-based localization systems. The main problem of the classical visual Simultaneous Localization and Mapping (SLAM) for underwater vehicles is the lack of robust, stable and matchable features in certain aquatic environments. The presence of sandbanks, seagrass or other underwater phenomena cause the visual features to concentrate in regions heavily textured, leaving great image areas completely free of visual information. In this situation, the classical loop closing detection algorithms fail, resulting in no corrections for the SLAM system. Our novel method proposes to reinforce the loop closing detection by clustering visual keypoints present in multiple keyframes and to match features of clusters instead of features of keyframes.

This new technique is assessed on the particular application of navigating an Autonomous Underwater Vehicle (AUV) in marine environments colonized with seagrass or with the presence of sandbanks. Experiments conducted in several coastal zones on the Balearic Islands show a high degree of success in the visual registration of overlapping areas.

Distributed embedded systems (DESs) that operate in dynamic environments require emerging flexibility and adaptivity communication requirements. When those DESs are deployed for critical applications, they must also employ appropriate fault-tolerance (FT) mechanisms to attain a high level of reliability. The FTT-Ethernet communication protocol supports the flexibility needed in dynamic environments, but does not provide adequate fault tolerance. In order to overcome this limitation the ongoing FT4FTT project proposes a communication architecture that includes fault-tolerance capabilities at different levels of DESs relying on FTT-Ethernet. In particular, it provides communication and execution mechanisms to tolerate node failures by means of active node replication with majority voting. This paper builds upon a previous OMNET++ model of an FTT-Ethernet-based DES in order to add, simulate and assess those mechanisms. Specifically, it models the communication mechanisms envisaged to enforce replica determinism in the voting procedure, as well as to trigger and coordinate the tasks executed in the replicas.

Distributed embedded systems (DES) have traditionally been designed assuming that the requirements they need to satisfy are known in advance. If this is not the case, and a DES should operate autonomously without interruption, it needs to be adaptive. For this, flexible approaches are necessary and this applies in particular to the network of the DES. However, if the probability of faults occurring is non-negligible, then flexibility alone is not enough and fault tolerance is also necessary. The Flexible Time-Triggered Replicated Star for Ethernet (FTTRS) is a set of protocols and mechanisms together with a specific network topology that builds on a switched-Ethernet implementation of the Flexible Time-Triggered (FTT) communication paradigm by enhancing it to not only provide flexibility, but also fault tolerance. This paper describes our efforts towards a layered architecture for FTTRS to benefit from the well-known advantages of these architectures, such as making the complexity manageable and easier to communicate, and making the design more future proof by allowing changes in one layer without affecting other layers.