User accuracy matters!
NAVCAST ultimate goal is to enhance user performance. User accuracy and convergence time achievable using NAVCAST corrections were tested using a PPP engine. The PPP engine, dual frequency, ionosphere free observations, estimates the local troposphere delays and fixes the carrier phase integer ambiguities and improves user position accuracy. The data used for visualization was recorded on October 18th 2018.
How good are NAVCAST clocks and orbits?
NAVCAST Galileo and GPS precise orbits and clocks have been compared to two IGS multi-GNSS (CODE and GFZ) centres over a one week period.
Tests were conducted in a fully realistic testing environment of the unmodified clock estimation software in real-time using 90 stations worldwide. Pre-stored observation data from all stations were used for generation of high-quality orbit solutions, 3-day arcs were processed and the central days were used for the assessment. GPS and Galileo orbits determined from the same network were also used as input for clock estimation.
Reference Stations used to generate R/T corrections
Orbit Accuracy, each millimetre counts!
We show the root-mean-square (RMS) orbit differences in radial (R), along-track (A) and cross-track (C) directions, the 3D errors direction and the “orbit-only-signal-in space range error” SISRE(orb).
SISRE(orb) constitutes a commonly acknowledged metric for orbit accuracy assessment and can directly be used to assess the impact of GNSS orbit errors on the user positioning performance.
We compared the benchmark NAVCAST orbit against two IGS multi-GNSS (CODE,GFZ) orbit products. Results show NAVCAST orbit determination accuracy is below 5cm RMS for individual components (R,A,C), 3D and the SISRE(orb):
Clock Accuracy, just wait a nanosecond …
For clock accuracy evaluation, we decided to follow the common practice of IGS clock product comparisons, to remove an epoch-wise constellation-mean clock difference and satellite specific clock biases. Here we also show the geographically averaged signal-in-space range error (SISRE) as a more appropriate performance measure than the actual clock difference (ΔClk).
We compared the benchmark NAVCAST clock against two IGS multi-GNSS (CODE, GFZ) clock products. Results show NAVCAST clock estimation accuracy is below 0.2ns RMS for ΔClk and the SISRE:
GPS Clock and Ephemeris Corrections
NAVCAST grows, welcome Biases!
Two new functionalities will be soon included in the NAVCAST core processor: Code and Phase biases. The code biases will allow satellite clock offset information, determined from a specific set of signals and frequencies, to be translated to other set of frequencies tracked by the receiver. The phase bias will fasten the ambiguity fix and users will obtain the ultimate accuracy within the shortest period of time.
The test performed with the newly available NAVCAST core processors for code biases (DCB) show accuracy (1 sigma) better than 10cm (0.33ns) when compared to IGS reference products (DLRMGX and CASMGX). The comparison between the two references is also in the same range as NAVCAST:
NAVCAST phase bias processor was confronted to similar tests. The ionospheric free linear combinations of the phase biases have been compared with a reference phase bias solution obtained with a larger network since no accepted references are available for phase biases. Results show that the phase biases accuracy (1 sigma) are below 0.5 cm.
Don’t stop the clock!
NAVCAST is fast. The latency on clock estimation is key for a real time service as NAVCAST. We have measured the time RETICLE needs to output a clock estimate depending on the number of stations. Results are below 1 second for a 90 stations network.