What is the practical effect of resolving carrier-phase ambiguities in GNSS?

• A. Enables decimeter-level precision.
• B. Enables centimeter-level precision.
• C. It has no effect.
• D. Only helps in RTK, not PPP.

Answer: (B)

Resolving carrier-phase ambiguities means determining the exact integer number of carrier cycles that separate the satellite signal from the receiver. The carrier-phase measurement is extremely precise, but it is only known up to an unknown integer number of wavelengths. Once those integers are fixed, the phase data can be used to its full precision, turning small phase differences into accurate distance measurements.

With the ambiguities fixed, the remaining error sources (like noise, clock, and atmospheric biases) have much less impact, so the positioning solution can reach centimeter-level accuracy in real time (RTK) or in PPP with ambiguity resolution (PPP-AR). Without fixing these ambiguities, you can still use phase data, but the accuracy remains much coarser, typically decimeter to meter level.

So, the practical effect is enabling centimeter-level precision.