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Positioning Application: Why does the GPS constellation file have a default global offset of +10dB?

Environment/Versions
  • PosApp (SimGEN, SimREPLAY+, SimREPLAY)
Answer
  1. Spirent simulators use -130dBm for the nominal signal reference for GPS L1 CA code. (See article FAQ14116 for further details).
    • This was based on Block 1 Satellites.  For modern satellites it would be closer to -128.5dBm.
    • This level is actually the minimum received level so would generally be higher than this when looking at live sky.
  2. The difference in thermal noise floor on the RF output from the simulator verses live sky is about 8dB.
  3. With the expected received signal level being higher than -130dBm (point 1 above), and a higher noise floor on the simulator verses the live sky (point 2 above), the power level output from the simulator needs to be increased.  
    • This is to ensure a receiver being connected to the RF output of the simulator sees approximately the same carrier to noise ratio as it would when looking at the live sky signals.  
    • So +10dB is used as the default level offset giving an output level of -120dBm.
  4. This default level can be modified by SimGEN users but is read only for SimREPLAY and SimREPLAY+ users.

 

Product : SimREPLAYplus,SimREPLAY,SimGEN,PosApp