The authors suggest that doppler velocity calculations should be immune to the kind of overestimation they claim sampling position measurements suffers from. I don't think this can be the case.
Let's first focus on what is wikipedia claims is the largest source of error: signal delay from the ionosphere. It seems reasonable to assume that this delay changes in a continuous manner with time. However, that means that the (non-shared) error introduced into position measurements as a result also shows up in the Doppler velocity estimations.
Indeed, one can think of Doppler velocity measurements as, at the theoretical limit of accuracy, being just another GPS measurement using the difference between the actual and expected number of wave creasts observed as the change in signal delay. Thus it would seem it would suffer the exact same problem as a sophisticated position sampling approach.
Non-continuous errors might be different, e.g., multi-path effects, but these should result in greater Doppler velocity errors than positional errors (the position error shouldn't be at most approximately the distance of the receiver from the source of the reflection while the Doppler velocity measurement could be totally reversed).
Am I missing something?