Project description SSRoverDAB+

In Germany, precise GNSS corrections are provided by the SAPOS service of the Working Committee of the Surveying Authorities (AdV) as part of the Open Data Initiative. To access and use the corrections, users rely on mobile internet, a widely accepted transmission medium, as well as the RTCM 3.x correction data format and the RTK positioning method.

Due to gaps in cellular network coverage, nationwide correction reception via mobile internet cannot be guaranteed. In order to enable correction data reception even in mobile internet dead spots, commercial service providers broadcast the corrections in parallel via geostationary satellites. Since the correction data is available in the service provider’s proprietary format, the user needs a GNSS receiver from the same provider.

To expand the coverage area of the SAPOS service, parallel transmission of the precise correction information via other data channels, such as DAB+, is preferred. To save data bandwidth and avoid loss of accuracy during the broadcast process, the new PPP-RTK data delivery and positioning technique will be used. Currently, neither an internationally standardised PPP-RTK data format, nor a commercial GNSS rover system capable of processing the corrections are available.

The project aimed to generate a broadcast-capable PPP-RTK correction data stream in an open data format with optimised bandwidth based on an existing GNSS reference station network. In addition, a reliable DAB+ data transmission channel was established and precise real-time PPP-RTK positioning and sensor fusion algorithms were developed and adapted. The Alberding A10-RTK sensor was used as a development and demonstration platform for extensive testing of the overall solution in practical field tests.

The following tasks were identified based on the assessment of the initial situation and the goals of the project:

The first two tasks were provided by the associated partners AdV, represented by the Bavarian Agency for Digitisation, High-Speed Internet and Surveying (LDBV), and the Federal Agency for Cartography and Geodesy (BKG). The associated project partner BayWa supported the definition of requirements and the practical field tests.

In general, the scope of the work can be divided into improvements in the DAB+ transmission infrastructure and developments for a user terminal that receives the DAB+ transmissions and uses PPP-RTK corrections for cm-accurate positioning. On the GNSS infrastructure side, models for the transmission of regional ionospheric and tropospheric parameters in dedicated time slots have been developed and the coding for the DAB+ transmissions has been optimised.

The majority of the work went into the development of software and system solutions for precise GNSS posi¬tioning using PPP-RTK corrections received from DAB+ transmissions. The existing Alberding A10-RTK hardware was used as a test and evaluation platform for the software developments in the project. Three different positioning solutions using PPP-RTK corrections were developed in the project and have been successfully implemented on the embedded PC inside the A10-RTK sensor.

For an optimal mobile DAB+ reception, a DAB+ receiver module has been developed, produced and tested with different antennas. To transform the positions from the roof to the wheel of an agricultural machine, an algorithm using INS data was developed. Because of the INS sensor and the DAB+ receiver did not fit into the A10-RTK form factor, new A10-DAB+ prototype sensors had been manufactured. The A10-DAB+ sensor combines all necessary components for the system functionality tests in one housing.

Practical field tests have been carried out successfully on agricultural machines in Bavaria. The A10-DAB+ sensor received PPP-RTK corrections via DAB+ transmissions, converted the spacebased corrections into observation-based RTCM 3.2 MSM messages and transmitted the corrections to the integrated RTK rover on the machine. The corrections were accepted by the rover and used by the automatic-steering system of the machine. The tractor terminal showed an RTK positioning accuracy of 1-2 cm.

As the principal usage of PPP-RTK transmission via DAB+ has been proven in the SSRoverDAB+ project, future efforts should also focus on the development of a combined sensor solution that uses DAB+ modules which can be produced in quantities in a smaller form factor and at a lower price.

Detailed information can be found in the final presentation and in the press release on the project conclusion (German).

05/2022 - 06/2023

"SSRoverDAB+" was funded under the 2nd element of the " Navigation Innovation and Support Programme" of the European Space Agency ESA (ESA NAVISP Element 2). The programme aims to develop innovative competitive products in satellite navigation and other areas of positioning, navigation and timing.