This paper presents the integration of an Ultra Short Base Line (USBL) acoustic modem and positioning device in a two-parallel Extended Kalman Filter (EKF) multisensor navigation schema for an Autonomous Underwater Vehicle (AUV). The system consists of a first odometric EKF position estimator fed with the measurements provided by an Inertial Measurement Unit (IMU), a Doppler Velocity Log (DVL), a visual tracker and a pressure sensor, and a second corrective EKF that fuses the previous sensors with the Global Positioning System (GPS) and the corrected delayed-state Ultra Short Base Line (USBL) position data. The first filter is aimed to compute a highly reliable vehicle position estimation from the sensor suit that produces high frequency relative navigation data. This estimation is essential to correct the delay of the USBL position measurements. The objective of the second filter is to give the vehicle a global pose, eliminating the drift inherent to dead reckoning sensors by integrating absolute positions (GPS and USBL) provided at low frequencies. The effects of the USBL integration in the global localization module are evaluated in a simulated environment, and compared to a ground truth trajectory with the pose estimates given by the first EKF, the USBL raw data and the output of the second EKF, showing an effective reduction of the trajectory error.
Publication type: Conferences
Distributed Embedded Control Systems (DECSs) used for Real-Time (RT) critical applications must satisfy stringent time requirements and attain high reliability. FTT-Ethernet provides nodes of DECSs with real-time communication capabilities, but does not include Fault Tolerance (FT) mechanisms. The FT4FTT project aims at proposing a complete FT architecture for RT critical DECSs. It uses a duplicated switched FTT-Ethernet star and active node replication with consistent distributed majority voting to respectively tolerate channel and node faults. However, FT4FTT, in its current state, still lacks mechanisms to prevent node redundancy attrition due to temporary faults affecting the nodes and channel, which are the most likely types of faults in DESs. This paper presents our ongoing work to complete the FT4FTT architecture with appropriate fault-diagnosis and reintegration mechanisms that overcome this limitation.
Ethernet is gaining importance in fields such as automation, avionics and automotive. In these fields novel multimedia-based applications must coexist with traditional control systems, which leads to high diversity in size, intensity and timing requirements of the traffic traversing the channel. Multimedia traffic is characterised by having large size, low intensity and soft real-time requirements, while control traffic usually conveys small amounts of information with a high intensity and hard real-time requirements. Moreover, many modern applications must support on-line connection and disconnection of participants. Since Ethernet was designed as a general purpose data network protocol it lacks appropriate support for real-time communications and dynamic quality of service management. Several protocols were proposed to cope with these drawbacks, including Flexible Time-Triggered Switched Ethernet and, more recently, Audio Video Bridging. In this paper we discuss the importance of the admission control and make a comparison of the implementations carried out in the aforementioned protocols.
Distributed embedded systems typically have real-time and dependability requirements. Moreover, they must also be flexible to changing conditions when they are deployed in dynamic environments. The FT4FTT project aims at providing a switched Ethernet architecture that can support distributed control applications that are predictable, highly-reliable and adaptive. FT4FTT relies on the Flexible Time-Triggered Replicated Star for Ethernet (FTTRS) to tolerate channel faults. Moreover, nodes’ hardware faults are tolerated by means of active node replication with majority voting. In order to coordinately trigger the execution of the tasks in the replicas, we designed the CD4NR mechanism, in which the network assists in deciding what to execute and when. This paper presents the first implementation
of the CD4NR mechanism on a real prototype of FTTRS and the first testing of the complete system. For this we developed an experimental setup, based on the hardware-in-the-loop technique, running a real-time control application.
Best WiP Paper Award