I mean if the candidate would insist that the smartphone sends a signal to the satellite, you can go on and ask "what kind of data?" -"Nothing, just a PING to w

I mean if the candidate would insist that the smartphone sends a signal to the satellite, you can go on and ask "what kind of data?" -"Nothing, just a PING to which the satellite answers with a PONG that contains its position". This is not at all how GPS works, but this system would also work (in a sense you could determine your position on earth based on the RTT + transmitted satellite coordinate). It is not that the candidate should come up with a perfectly correct solution (actually this could be bad because he could just blindly repeat what he/she read without understanding it) - its whether he/she can come up with a solution for the problem at all. In the interview you could still go into discussion about that approach then (what about undirected energy dissipation for contacting a thousands-of-km away satellite, and problems with time-multiplexing transmissions now on the satellite that has to answer individual requests vs broadcast etc.).