  In this paper, we focus on the coexistence between a MIMO radar and cellular
base stations. We study the interfering channel estimation, where the radar is
operated in the "search and track" mode, and the BS receives the interference
from the radar. Unlike the conventional methods where the radar and the
cellular systems fully cooperate with each other, in this work we consider that
they are uncoordinated and the BS needs to acquire the interfering channel
state information (ICSI) by exploiting the radar probing waveforms. For
completeness, both the line-of-sight (LoS) and Non-LoS (NLoS) channels are
considered in the coexistence scenario. By further assuming that the BS has
limited a priori knowledge about the radar waveforms, we propose several
hypothesis testing methods to identify the working mode of the radar, and then
obtain the ICSI through a variety of channel estimation schemes. Based on the
statistical theory, we analyze the theoretical performance of both the
hypothesis testing and the channel estimation methods. Finally, simulation
results verify the effectiveness of our theoretical analysis and demonstrate
that the BS can effectively estimate the interfering channel even with limited
information from the radar.
