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With the growing demand for GNSS application, the satellite navigation payload may supply several signal components and modulation types in each frequency. This trend will continue for the future GPS/Galileo/Compass system. In order to provide a precision positioning service, the satellite navigation payload must supply a continuous, precise and high integrity signal. The signal quality is determined by the linear distortion and the non-linear distortion in the payload system. The non-linear distortion can be decreased by the constant envelope signal modulation. This paper will study the arithmetic of Coherent Adaptive Subcarrier Modulation (CASM) for 4-signal case and the modeling algorithm of pre-post filter/high power amplifier (HPA). At last, the ideal receiver will give the precision of ranging.