GNSS Receiver Vector Tracking Loops for Autonomous Vehicles (VTL4AV)
As part of the European Space Agency’s (ESA’s) Navigation Innovation and Support Programme (NavISP), Telespazio UK, alongside its project partners Cranfield University and Spirent Communications, is working on a project to develop GNSS Receiver Vector Tracking Loops for Autonomous Vehicles (VTL4AV).

Global Navigation Satellite Systems (GNSS) have become the primary means of navigation and source of Position, Navigation and Timing (PNT) information for almost all modes of transport, general navigation and for timing purposes. Yet, all GNSS are vulnerable to natural interference, deliberate and accidental jamming, and spoofing. Moreover, because of the geometry of GNSS flying in Medium Earth Orbit and the number of satellites in the constellation, there are other issues.

Where users are operating in so-called “urban canyons”, or within dense vegetation, or in deep valleys for instance, they can have a limited view of the satellites and hence have trouble calculating a position. In these situations, multipath propagation is also a problem, causing receivers to calculate an incorrect position from erroneous and altered signals. Clearly, this is unacceptable when operating a safety-critical service, or when other safety parameters are paramount. Such a situation is operating autonomous vehicles in public areas.

In conventional GNSS receivers, satellite tracking is performed in several independent “tracking loops” that provide measurements to a navigation algorithm, creating a navigation solution. Using “Vector Tracking Loops” (VTL), the two tasks of signal tracking and signal estimations are combined; however, VTL architectures are sensitive to channel contamination and data incest. It is therefore required to combine the benefits of VTL with other PNT sensors.

To tackle these challenging problems, the VTL4AV project will design and develop a receiver implementing these VTL techniques including fusion with external sensors such as LiDAR, visual and inertial using various type of receiver architectures (usually loose coupling and tight coupling when using GNSS, but also ultra-tight coupling architectures utilising the benefits of inertial measurements to improve receiver tracking). The project will also create a fault detection and isolation strategy to ensure integrity in urban environments, whilst supporting multiple GNSS constellations. The benefits of this architecture will be demonstrated in both simulated environments and in a real environment such as the City of London where urban canyons, signal masking, interference and multipath can be expected.

The VTL4AV project will investigate, consolidate and develop new algorithms, waveforms, software, and hardware, to evolve the VTL4AV concept to a viable component of a resilient PNT for autonomous vehicles.