GLONASS satellites transmit two types of signal: a standard precision (SP) signal and an obfuscated high precision (HP) signal.
All satellites transmit the same code as their SP signal; however each transmits on a different frequency using a 15-channel frequency division multiple access (FDMA) technique spanning either side from 1602.0 MHz, known as the L1 band. The equation to calculate the exact center frequency is 1602 MHz + n × 0.5625 MHz, where n is a satellite’s frequency channel number (n=−7,−6,−5,…,7). Signals are transmitted in a 38° cone, using right-hand circular polarization, at an EIRP between 25 to 27 dBW (316 to 500 watts). Note that the 24 satellite constellation is accommodated with only 15 channels by using identical frequency channels to support antipodal (opposite side of planet in orbit) satellite pairs, as these satellites will never be in view of an earth based user at the same time.
The HP signal is broadcast in phase quadrature with the SP signal, effectively sharing the same carrier wave as the SP signal, but with a ten times higher bandwidth than the SP signal.
The L2 signals use the same FDMA as the L1 band signals, but transmit straddling 1246 MHz with the center frequency determined by the equation 1246 MHz + n×0.4375 MHz, where n spans the same range as for L1. Other details of the HP signal have not been disclosed.
At peak efficiency, the SP signal offers horizontal positioning accuracy within 57–70 meters, vertical positioning within 70 meters, velocity vector measuring within 15 cm/s, and timing within 1 µs, all based on measurements from four satellite signals simultaneously. The more accurate HP signal is available for authorized users, such as the Russian Military.
Currently, an additional civil reference signal is broadcast in the L2 band with an identical SP code to the L1 band signal. This is available from all satellites in the current constellation, except satellite number 795 which is the last of the inferior original GLONASS design, and one partially inoperable GLONASS-M satellite which is broadcasting only in the L1 band. (see glonass-ianc.rsa.ru for daily updates on constellation status.)
GLONASS uses a coordinate datum named “PZ 90” (Parametry Zemli 1990), in which the precise location of the North Pole is given as an average of its position from 1900 to 1905. This is in contrast to the GPS’s coordinate datum, WGS 84, which uses the location of the North Pole in 1984. As of September 17, 2007 the PZ-90 datum has been updated to differ from WGS 84 by less than 40cm in any given direction.
Glonass-KM satellites will be launched by 2025. Additional open signals are being studied for these satellites, based on the same frequencies and formats as GPS signals L5 and L1C and corresponding Galileo/COMPASS signals E1, E5a and E5b. These signals include:
- The open signal L1OCM will use BOC(1,1) modulation centered at 1575.42 MHz, similar to modernized GPS signal L1C and Galileo/COMPASS signal E1;
- The open signal L5OCM will use BPSK(10) modulation centered at 1176.45 MHz, similar to the GPS “Safety of Life” (L5) and Galileo/COMPASS signal E5a;
- The open signal L3OCM will use BPSK(10) modulation centered at 1207.14 MHz, similar to Galileo/COMPASS signal E5b.
Such an arrangement will allow easier and cheaper implementation of multi-standard GNSS receivers.