What is the satellite naming convention in RTK injection bar chart?

[JiaRong-Zhan (佳融 詹)]

Hello everyone.
I have a question about the bar chart .

The satellite name in the red circle are GXX、RXX、EXX、BXX…etc.
Could anyone tell me what is the satellite naming convention?
At first I thought that mean "G"ps、"G"lonass 、"B"eidou、"G"alileo,but it too much “G” name .

Thank you for reading!

[Eosbandi (Andras Schaffer)]

R is Russian Glonass
E is European Galileo
G is American GPS
B is Chinese Beidou

[JiaRong-Zhan (佳融 詹)]

Thank you for helping!
It helped me a lot