  This paper proposes the transmission of beacon signals to alert potential
interferers of an ongoing or impending passive sensing measurement. We focus on
the interference from Low-Earth Orbiting (LEO) satellites to a radio-telescope.
We compare the beacon approach with two versions of Radio Quiet Zones (RQZs):
fixed quiet zones on the ground and in the sky, and dynamic quiet zones that
vary across satellites. The beacon-assisted approach can potentially exploit
channel reciprocity, which accounts for short-term channel variations between
the satellite and radio telescope. System considerations associated with beacon
design and potential schemes for beacon transmission are discussed. The
probability of excessive Radio Frequency Interference (RFI) at the radio
telescope (outage probability) and the fraction of active links in the
satellite network are used as performance metrics. Numerical simulations
compare the performance of the approaches considered, and show that the beacon
approach enables more active satellite links relative to quiet zones for a
given outage probability.
