Differences between GNSS constellations

What does GLONASS functionality add?

The addition of GLONASS functionality doesn’t necessarily improve the position/orientation accuracy of an INS , but it does increase the number of satellites available for the system to track. From our observations, with GLONASS functionality you typically track about 50 % more satellites than with GPS alone. For example, if you were tracking 6 GPS satellites, you may observe an additional 3 GLONASS satellites. 

A situation where GLONASS could improve position accuracy would be if you were tracking 4 GPS satellites. This is the minimum number of satellites required for a position fix. When you track 4 satellites you are usually in a poor GNSS environment and position accuracy is relatively low. If you were to add GLONASS functionality, then you may be able to track a further 2 satellites, taking the total up to 6 satellites. This would give you better position accuracy than 4 satellites.

Note that the position accuracy would be the same whether you are tracking 6 GPS satellites, or a combination of GPS+GLONASS (i.e. 4 GPS + 2 GLONASS). If you are in a good GNSS environment and tracking, say, 9 GPS satellites, then GLONASS would not improve the position accuracy even though you may be tracking 15 satellites in total.

The G5Ant-2AMNS1 antennas supplied with high precision units (RT2002, RT3002 and RT3003), are GLONASS capable, so the upgrade to GLONASS requires and auth code sent to the GPS card, which can be carried out by the user once supplied by OxTS. The AT575-70 antennas supplied with lower precision units (RT3200, RT3202, RT3100 and RT3102), are not GLONASS capable, so in addition to the auth code you would require new antennas.

It is possible to upgrade most RT-Base-2 units to RT-Base-2G models using an auth code. You can use base stations and RT units with and without GLONASS in the following combinations:

• RT-Base-2 with RT3003: GPS corrections received. RTCA, RTCA2 and RTCMv3 modes supported.
• RT-Base-2G with RT3003: GLONASS corrections are ignored by the RT3003, only GPS corrections used. RTCA, RTCA2 and RTCMv3 modes supported.
• RT-Base-2 with RT3003G: no GLONASS corrections transmitted by base station, so only GPS corrections used. RTCA, RTCA2 and RTCMv3 modes supported.
• RT-Base-2G with RT3003G: full GPS and GLONASS functionality and corrections used in RTCA2 and RTCMv3 modes. In RTCA mode only GPS corrections will be used.