Digital down-conversion in software defined radios in space-to-Earth and Earth-to-space communications is challenging due to potentially large Doppler frequency offsets. The predictability of satellite orbits suggests that a computed Doppler offset could be used to perform an orbit-informed down-conversion. However, publicly available orbital parameters and orbit propagator codes lack the accuracy required for fine Doppler removal. This paper proposes a technique to adjust the orbital parameters until the computed Doppler profile matches the Doppler profile in the received signal. This technique is applied to a real signal recorded from a satellite overpass and is shown to be able to very accurately estimate frequency offsets.

Online services collect personal data from their users, sometimes with no clear need. We studied how users sign-in to web sites using federated IDs, and found that most survey respondents were not aware of the data they expose. However, when presented with the tradeoffs behind each sign-in option, respondents reported a willingness to change how they sign-in to reduce their data exposure or, in fewer cases, to increase it to receive more benefits from the service. Our findings suggest that data exposure is a concern for users, and that there is a need for finding clearer ways for communicating it for each sign-in option.