Techniques are provided for utilizing a mobile device to estimate ionospheric delays in GNSS transmissions. An example method of determining a position of a mobile device includes obtaining a pseudorange measurements and carrier-phase measurements for a satellite at a first frequency band and a second frequency band, determining a bias estimate for the satellite based on a plurality of pseudorange measurements and carrier-phase measurements, determining a delta carrier-phase measurement for the satellite based on the carrier-phase measurements at the first frequency band and the second frequency band, and determining the position of the mobile device based at least in part on the delta carrier-phase measurement, and the pseudorange measurements, the carrier-phase measurements, or both.