  This paper considers the uplink of a massive MIMO communication system using
5G New Radio-compliant multiple access, which is to co-exist with a radar
system using the same frequency band. A system model taking into account the
reverberation (clutter) produced by the radar system onto the massive MIMO
receiver is proposed. In this scenario, several receivers for uplink channel
estimation and data detection are proposed, ranging from the simple
channel-matched beamformer to the zero-forcing and linear minimum mean square
error receivers for clutter disturbance rejection, under the two opposite
situations of perfectly known ad completely unknown clutter covariance. A
theoretical analysis is also given, deriving a lower bound on the achievable
uplink spectral efficiency and the mutual information between the input
Gaussian-encoded symbols and the observables available at the communication
receiver of the cellular massive MIMO system: regarding the latter, in
particular, we show that, in the large antenna number regime, the radar clutter
effects at the base station is suppressed and single-user capacity is restored.
Numerical results, illustrating the performance of the proposed detection
schemes, confirm the findings of the theoretical analysis, and permit
quantifying the system robustness to clutter effect for increasing number of
antennas at the base station.
