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Global Navigation Satellite Systems (GNSS) – Dr. Boris Vassilev
Posted: 18 October, 2015

Global Navigation Satellite Systems (GNSS) – Dr. Boris Vassilev

The week 12 October – 18 October was dedicated to GNSS and the main role was played by Dr. Boris Vassilev who had the tough task on 13 October to present an introduction to satellite navigation systems in no more than two hours. He is a former Bulgarian Air Force engineer and Prof. in Aeronautical Department of Technical University – Sofia. Dr. Vassilev has extensive experience with GNSS ranging from working with EUROCONTROL to validate EGNOS for aviation to preparing and presenting science papers on Science conferences around the world. Some info about B.Vassilev:

What is navigation? If you think practically – every part of our life is navigation.

This is how Dr. Boris Vassilev started his lecture about Global Navigation Satellite Systems (GNSS).

We can’t be lost, said Gurder. We’re here. We know where we are. We just don’t know where we aren’t.

After that he spoke about the inertial frame of reference and about the coordinate systems: Earth-Centered Coordinate System, Earth-Fixed Coordinate System & World Geodetic System (WGS 84). He said that the most well know coordinate system is the Geographic coordinate system. It uses measures of latitude and longitude in order to determine the location.

The Time Determines The Space

Satellites: They are in SPACE and stay there by going so fast that they are never in one place enough to fall down. TELEVISIONS are bounced off them… They are past of SCIENCE. Terry Pratchet – “Wings”

Dr. Vassilev continued his lecture with GNSS-1. This is the first generation system and is the combination of existing satellite navigation systems (GPS and GLONASS) with Satellite Based Augmentation Systems (SBAS) or Ground Based Systems (GBAS). After that he talked about GNSS-2, which is the second generation of systems. It independently provides full civilian satellite navigation systems, exemplified by the European Galileo positioning system. Last but not least, Dr. Boris Vassilev mentioned the world’s most utilized satellite navigation system – GPS.

Dr. Vassilev impressed the audience with the fact that the navigation message takes 50bits per second.

Another very interesting thing was to understand that GPS has two codes. The C/A code repeats after 1 ms. However the so called P-code (the military one) is being changed once in every 37 weeks.

In the end Dr. Boris Vassilev talked about the sources of GNSS error: satellite clocks, orbital errors, ionosphere, troposphere, receiver noise and of course the multipath.


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