what GNSS signals do we have …
It is interesting sometimes to take a step back and remember what signals we actually have as they limit completely what we can accomplish. It has been amazing what engineers worldwide have been doing with these basic and limited signals. Noone at the start of GPS could have imagined the number of applications and how well the brilliant world-wide engineers have made them work.
So to take the step back we go back to the basic GPS and GLONASS signals. There are two frequencies being used by each GNSS satellite on the L-band. GPS uses the same frequencies for each satellite 1575 MHz (L1) and 1227 MHz (L2) and encodes ranging messages on both. GLONASS uses two distinct frequencies for each satellite (although antipode satellites may use the same frequencies) the GLONASS frequency ranges are 1610.6-1613.8 MHz (L1) and 1240-1260 MHz (L2).
The ranging messages encoded on the L1 signal give the following ranging information:
- C1 ; Ranging to the satellite based on the Civil message.
- P1 ; Ranging to the satellite based on the Encrypted (high-security) message.
- L1 ; Number of cycles since satellite acquisition.
on L2 we have:
- P2 ; Ranging to the satellite based on the Encrypted (high-security) message.
- L2 ; Number of cycles since satellite acquisition.
a limited number of satellites are transmitting C2 now but not many receivers are providing this signal regularly. until a significant number of satellites have C2 capabilities it will remain an oddity in the constellation. Preliminary studies suggest the signal is good but for receivers that provide P2 this one is preferred. The issue of the P2-C2 calibration has also to be addressed as it has been for the P1-C1 bias in case of mixing the measurements in any calculations.
Good luck!
