  Spectrum sharing is a new approach to solve the congestion problem in the RF
spectrum. A spatial approach for spectrum sharing between a radar and a
communication system was proposed, which mitigates the radar interference to
communication by projecting the radar waveform onto the null space of the
interference channel, between radar and communication system [1]. In this work,
we extend this approach to a maritime MIMO radar which experiences a time
varying interference channel due to the oscillatory motion of a ship, because
of the breaking of sea/ocean waves. We model this variation by using the matrix
perturbation theory and the statistical distribution of the breaking waves.
This model is then used to study the impact of perturbed interference channel
on the spatial approach of spectrum sharing. We use the maximum likelihood (ML)
estimate of a target's angle of arrival to study the radar's performance when
its waveform is projected onto the null space of the perturbed interference
channel. Through our analytical and simulation results, we study the loss in
the radar's performance due to the null space projection (NSP) of its waveform
on the perturbed interference channel.
