  Co-existence between unlicensed networks that share spectrum
spatio-temporally with terrestrial (e.g. Air Traffic Control) and shipborne
radars in 3-GHz band is attracting significant interest. Similar to every
primary-secondary coexistence scenario, interference from unlicensed devices to
a primary receiver must be within acceptable bounds. In this work, we formulate
the spectrum sharing problem between a pulsed, search radar (primary) and
802.11 WLAN as the secondary. We compute the protection region for such a
search radar for a) a single secondary user (initially) as well as b) a random
spatial distribution of multiple secondary users. Furthermore, we also analyze
the interference to the WiFi devices from the radar's transmissions to estimate
the impact on achievable WLAN throughput as a function of distance to the
primary radar.
