Browsing by Author "Negru, Sorin Andrei"

Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Design and hardware-in-the-loop evaluation of a time dissemination framework for drone operations in urban environments
    (IEEE, 2023-11-10) Negru, Sorin Andrei; Petrunin, Ivan; Guo, Weisi; Tsourdos, Antonios
    With the advent of UAVs (Unmanned Aerial Vehicles) several companies started to offer services, in urban, semi-urban, and rural regions. Although GNSS (Global Navigation Satellite System) can disseminate time information to different platforms, external factors may degrade the signal quality and lead to erroneous time synchronization. The paper is presenting a resilient time dissemination framework, using a wireless 802.11ax protocol and NTP (Network Time Protocol) for the synchronization aspect. A time server, formed by a rubidium clock, a GNSS receiver, and time information provided by NPL (UK’s National Physical Laboratory) traceable to UTC, dictates the time to all the users within the WLAN (Wireless Local Area Network). To evaluate the proposed framework, a lab-based HIL (Hardware in the Loop) simulation is performed using two Jetson Nanos as CC (Companion Computer) and a Pixhawk 2.4 as FCU (Flight Control Unit) representing the end-users in the dissemination framework. In this way, all the communication links are tested and evaluated. Results showed that the two platforms can be synchronized to the time server as an alternative time source, achieving an average RTT (Round Trip Delay) of 8 ms from the Research and Innovation timing node to the FCU, and an average time offset of -0.2 ms.
  • Thumbnail Image
    ItemOpen Access
    Resilient multi-sensor UAV navigation with a hybrid federated fusion architecture
    (MDPI, 2024-02-02) Negru, Sorin Andrei; Geragersian, Patrick; Petrunin, Ivan; Guo, Weisi
    Future UAV (unmanned aerial vehicle) operations in urban environments demand a PNT (position, navigation, and timing) solution that is both robust and resilient. While a GNSS (global navigation satellite system) can provide an accurate position under open-sky assumptions, the complexity of urban operations leads to NLOS (non-line-of-sight) and multipath effects, which in turn impact the accuracy of the PNT data. A key research question within the research community pertains to determining the appropriate hybrid fusion architecture that can ensure the resilience and continuity of UAV operations in urban environments, minimizing significant degradations of PNT data. In this context, we present a novel federated fusion architecture that integrates data from the GNSS, the IMU (inertial measurement unit), a monocular camera, and a barometer to cope with the GNSS multipath and positioning performance degradation. Within the federated fusion architecture, local filters are implemented using EKFs (extended Kalman filters), while a master filter is used in the form of a GRU (gated recurrent unit) block. Data collection is performed by setting up a virtual environment in AirSim for the visual odometry aid and barometer data, while Spirent GSS7000 hardware is used to collect the GNSS and IMU data. The hybrid fusion architecture is compared to a classic federated architecture (formed only by EKFs) and tested under different light and weather conditions to assess its resilience, including multipath and GNSS outages. The proposed solution demonstrates improved resilience and robustness in a range of degraded conditions while maintaining a good level of positioning performance with a 95th percentile error of 0.54 m for the square scenario and 1.72 m for the survey scenario.