It's not just precision, but availability of the signal and speed. Having more signals in natural and urban canyons improves accuracy and speed when there are more satellites.
One-chip GPS/GLONASS multiconstellation receivers have been on the market for some time. Millions of consumer units sold. Many smartphones have them.
Quad-constellation (GPS, GLONASS, Galileo, BeiDou) receiver chips have been on the market for some time.
For example: STA8090GA, It's automotive Grade GPS/Galileo/Glonass/Beidou/QZSS receiver
One-chip GPS/GLONASS multiconstellation receivers have been on the market for some time. Millions of consumer units sold. Many smartphones have them.
Quad-constellation (GPS, GLONASS, Galileo, BeiDou) receiver chips have been on the market for some time.
For example: STA8090GA, It's automotive Grade GPS/Galileo/Glonass/Beidou/QZSS receiver
http://www.st.com/content/ccc/resource/technical/document/da...