GLONASS significantly benefits GPS
OxTS tests have shown that RT products with GPS and GLONASS manage to maintain lock on RTK Integer position measurements in locations where GPS only products cannot. The dual-frequency GPS and GLONASS products are able to relock much faster than their GPS-only counterparts too. There are now 20 GLONASS satellites in orbit, nearly a full constellation, so GLONASS always adds a significant number of satellites to GPS.
In open sky conditions, typical of most vehicle proving grounds, GPS works almost perfectly and users rarely see any drops in signal quality. However, many Advanced Driver Assistance System (ADAS) tests take place on public roads where the GPS conditions are variable. Using a product that supports both GPS and GLONASS on the public road can significantly increase the probability of having a very accurate solution.
Our recent tests compared dual-frequency GPS to dual-frequency GPS and GLONASS receivers on a section of road with trees close to both sides of the road. A single bridge on the route forced the products to lose their ambiguity lock twice during each lap. 8 laps were driven in order to generate some meaningful statistics.
Results showed that the dual-frequency GPS and GLONASS product maintained an RTK Integer position solution for 92% of the time, compared to 82% for the GPS-only product. The average relock time was just over 8 seconds for the GPS and GLONASS product compared to just over 14 seconds for the GPS-only product. Clearly the conditions affect the actual results so these numbers cannot be compared to data collected by other people but they can be compared to each other.
The GPS and GLONASS product also had less velocity noise. Velocity errors are a major source of drift when no satellite position is available and so, by improving the velocity, we also improve the drift of the inertial navigation system when GPS is removed.
Russia has made great progress with GLONASS in the last three years. Nearly all of the satellites have been launched since 2007 and several more are planned for next year. This rapid increase in the number of satellites makes GLONASS suitable today compared to the past.
The full OxTS report is available here...If you would like to find out more then please contact one of our sales representatives.