  The problem of covert communication over Multiple-Input Multiple-Output
(MIMO) Additive White Gaussian Noise (AWGN) channels is investigated, in which
a transmitter attempts to reliably communicate with a legitimate receiver while
avoiding detection by a passive adversary. The covert capacity of the MIMO AWGN
is characterized under a variational distance covertness constraint when the
MIMO channel matrices are static and known. The characterization of the covert
capacity is also extended to a class of channels in which the legitimate
channel matrix is known but the adversary's channel matrix is only known up to
a rank and a spectral norm constraint.
