  Reliable communication over delay-constrained block-fading channels with
discrete inputs and mismatched (imperfect) channel state information at the
transmitter (CSIT) is studied. The CSIT mismatch is modeled as Gaussian random
variables, whose variances decay as a power of the signal-to-noise ratio (SNR).
A special focus is placed on the large-SNR decay of the outage probability when
power control with long-term power constraints is used. Without explicitly
characterizing the corresponding power allocation algorithms, we derive the
outage exponent as a function of the system parameters, including the CSIT
noise variance exponent and the exponent of the peak power constraint. It is
shown that CSIT, even if noisy, is always beneficial and leads to important
gains in terms of exponents. It is also shown that when multidimensional
rotations or precoders are used at the transmitter, further exponent gains can
be attained, but at the expense of larger decoding complexity.
