The spectral separation coefficient (SSC) is used as a major parameter
for the assessment of GNSS radio frequency compatibility. As the
computation load to calculate the SSC is extremely intensive, one way to
simplify the SSC calculation is to replace the factor "signal power spectral density" by "code chip power spectral density". However, this approach will introduce greater error in certain situation. This paper analyses the influence of the signal’s power spectral density (PSD), length of spreading code, code chip rate and data rate of navigation signals on SSC. It suggests and proves a criterion that the simplified SSC calculation can be applied safely when signal's code length is greater than or equal to the ratio of code chip rate to data rate. The simplified calculation criterion proposed in this paper allows fast calculation of SSC so that compatibility amongst different GNSS
signals can be assessed quickly and accurately without introducing notable
calculation error.