Where does the ambiguity exist and why is it important?
Carrier phase measurements is the phase of the GNSS signal which remains when the incoming Doppler-shifted satellite carrier is differenced with the constant frequency generated in the receiver. Carrier phase observable is obtained as a by-product of the correlation channel or from a squaring channel. Because the wavelength of the carrier is much shorter than the wavelength of either of the codes, the precision of the carrier beat phase measurements is much higher than the precision of the code pseudoranges. The precision of the carrier phase measurements is key in Precise Point Positioning but also limits its performance, requiring 10's of minute convergence time to attain cm-level accuracy. If the ambiguity term is successfully resolved it will enable cm-level positioning within a few minutes. The ambiguity term within the carrier signal is the unknown number of whole wavelengths in an unbroken set of measurements from the satellite to a receiver.