High Accuracy GNSSTests under real conditions with assistance data
A GNSS receiver assisted by correction/augmentation data is capable of converging to a few centimeter accuracy.
Nevertheless, we designate a high accuracy service for measurements below one foot (33cm).
This performance depends on several conditions, including :
- Technologies of assistance services (PPP, PPP-RTK, RTK, NRTK,…);
- Density of the fixed reference station network;
- Number of GNSS frequency bands processed;
- Number of constellations supported by the used assistance service;
- Localization of the receiver in relation to the station networks ;
- Model of GNSS Receiver ;
- Model of GNSS signal reception antenna ;
- Availability and quality of the telecommunication means to transmit the assistance data ;
Figure 1 – Assessment of high accuracy GNSS performance
Static position accuracy is often the first characteristic put forward to define a receiver or an assistance service. However, other criteria are often much more decisive for the proper functioning of a given application, such as :
- Accuracy in dynamic mode, i.e. in motion;
- Resilience to disturbances in the local environment (bridges, foliage, infrastructure (multipath),…);
- Convergence time toward high accuracy;
- Self-estimation of errors;
- Sensitivity to telecommunication network hazards
Figure 2 – GNSS performance certification for high accuracy
MEANS OF METROLOGY
The measurement methods applied, to be useful, must be perfectly representative of use conditions. All the relevant elements (GNSS environment, assistance service, antenna, receiver, …) must be gathered to achieve to reliable results.
The ground truth must be consolidated with a reference instrumentation able to maintain the accuracy of the true trajectory followed by the antenna used in the tests.
Components of the reference instrumentation:
- Fixed station;
- Professional GNSS receiver and antenna;
- Inertial unit (angular measurements of the attitude<<0.1°);
- Odometer for data collection campaigns in constrained environments;
- Post-processing tools for GNSS (PPK) and inertial measurements;
This reference instrumentation then determines the quality of the results. Its measurements are assumed to be exact, modulo of the duly estimated uncertainties, and are compared with those of the test objects.
Figure 3 – Distribution of uncertainties according to the probability of remaining in the following measurement intervals., ie. 68% (1σ), 95% (2σ) and 99% (3σ)
GUIDE is accredited for its competence in the use of this instrumentation and the implementation of its methods. In particular, GUIDE guarantees the accuracy of the reference trajectories established and justifies the calculation of related measurement uncertainties.
Figure 4 – These instrumental uncertainties depend on both the instrumentation and the disturbances encountered on the path