Performance Evaluation of the Early CNAV Navigation Message

The GPS Directorate initiated a pre-operational routine generation and transmission of the Civil Navigation Message (CNAV) starting on 28 April 2014. CNAV data of the Block IIR-M and IIF satellites have been collected with a small set of globally distributed receivers. Starting in 2015, CNAV uploads are performed on a daily basis. Since then, the Signal-in-Space Range Error (SISRE) amounts to roughly 0.6 m, which is essentially identical to the LNAV SISRE for the same satellites. The new broadcast Inter-Signal Corrections (ISCs) agree with differential code biases derived in the frame of the IGS Multi-GNSS Experiment and DCBs from the Center for Orbit Determination in Europe on the 0.1–2 ns level depending on the ISC type. Use of these ISCs enables, for the first time, a consistent point positioning based on the exclusive use of civil L1C/A and L2C observations.