Comment Combining different GNSS systems is also an option (Score 4, Insightful) 44
Chances are that, when the GPS satellite is bouncing in the urban canyon, the Galileo one is in the zenit. And if you live in many countries where geopolitics are an aftertought, you can use GPS, Galileo, Glonass, and beidu, all at the same time. what's not to like?
Polish scientists have been doing this since 2018, probably there are even older efforts:
https://www.mdpi.com/2072-4292...
You combine that with cell tower location data, which is cheap, and Robert's your uncle.