GLONASS and GPS differences

You have probably already heard that there are actually TWO satellite constellations providing positioning signals available to everyone. the first is the well-known American GPS and the second is the Russian system GLONASS.

Both system do exactly the same thing. They provide a signal-in-space beamed down to earth from so-called Medium Earth Orbit (MEO) using dedicated satellites. Both systems provide a Civilian service and a “restricted” (Military) service.

The main differences as of now are:

  1. GLONASS is not complete. Whereas GPS has 32 satellites transmitting signals GLONASS only has 14 which does not guarantee world-wide coverage.
  2. GLONASS uses FDMA for its transmissions whereas GPS uses CDMA. in FDMA each satellite uses a different frequecy to transmit the same ranging code. in CDMA each satellite uses the same frequency with different ranging codes per satellite.
  3. GLONASS is providing a second Civilian signal on L2 which helps civilian users to properly eliminate the ionospheric error.
  4. GLONASS satellites are upgraded more often. This is due to a russian satellite design constraint or due to cost-saving measures but the GLONASS satellites have to be replaced much more often than GPS ones (every 5 to 7 yrs). This appears as a problem but it allows GLONASS to introduce new capabilities much faster than GPS.

The IGS provides precise orbit products and clocks for both constelations GLONASS and GPS as a public service. These orbits can be used together with precise GLONASS observations to perform the same type of calculations as with GPS observations. Many researchers are also supplementing GPS observations with GLONASS observations to increase precision and robustness of derived products.

Best Regards to all and Happy positioning.

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