Inter-frequency clock bias (IFCB) comes out when the GNSS observations employed by the user in positioning and the IGS analysis center in precise orbit&clock estimation are at different frequencies.
The precise satellite orbit and clock products from IGS are generated with the ionospheric-free combined code and carrier phase observations on the L1/L2, E1/E5a, B2I/B7I signals. The time-varying phase biases will be grouped with satellite clock ofset parameters. Therefore, the satellite clock estimates are different when using diferent ionospheric-free observations formed by the frst+second frequency and the frst+third frequency, respectively. This disagreement is the IFCB errors for the third-frequency GNSS data processing.
The corrections provided here can be used to remove the IFCB errors to make the L1/L2 based satellite clock bias corrections applicable for L5 observations.