  Discrete-time Rayleigh fading multiple-input multiple-output (MIMO) channels
are considered, with no channel state information at the transmitter and
receiver. The fading is assumed to be correlated in time and independent from
antenna to antenna. Peak and average transmit power constraints are imposed,
either on the sum over antennas, or on each individual antenna. In both cases,
an upper bound and an asymptotic lower bound, as the signal-to-noise ratio
approaches zero, on the channel capacity are presented. The limit of normalized
capacity is identified under the sum power constraints, and, for a subclass of
channels, for individual power constraints. These results carry over to a SISO
channel with delay spread (i.e. frequency selective fading).
