EVALUATION OF GPS BLOCK IIR TIME KEEPING SYSTEM FOR INTEGRITY MONITORING

摘要

Onboard GPS clock monitoring will be required for GPS III satellites. This paper will discuss some of the key integrity monitoring parameters in the context of the GPS Block IIR TKS. The paper will also show that: (1) the phase meter output, comparing the phase difference of the Rb Atomic Frequency Standard (AFS) and the VCXO in a 1.5-second GPS epoch, behaves like a Gaussian distribution; (2) The TKS probability of false alarm is almost equal to zero due to its rather large detection threshold; (3) The TKS can detect and compensate for "large" VCXO frequency steps with no significant TKS output phase error; (4) The TKS cannot compensate "large" VCXO frequency drift steps and may require a MCS (Master Control Station) contingency upload to remove phase bias; (5) The TKS cannot detect "large" AFS frequency steps or frequency drift steps that cause the TKS output phase error to run away, but steps of that type have not be observed in IIR operation so far.