How does a Swift GNSS chipset estimate velocity?

[Kiyoung Kim]

Currently, I am doing research in mitigating the noise in the GNSS velocity signal with Piksi Multi modules.

To the best of my knowledge, there are three methods to estimate velocity in a GNSS module: (1) Simply calculate distance/time, (2) estimate from the Doppler frequency shift, and (3) using time-differenced carrier phase technique.

I am really wondering which method the chipset uses for estimating the velocity, to figure out the relation between the noise in the velocity and the position measurement. Could anybody give me some information about the method applied to the module?