Coded modulation with mismatched power control over block-fading channels

Communication over delay-constrained block-fading channels with discrete inputs and imperfect channel state information at the transmitter (CSIT) is studied. The CSIT mismatch is modeled as a Gaussian random variable, whose variance decays as a power of the signal-to-noise ratio (SNR). We focus on the large-SNR behavior of the outage probability when transmit power control is used. 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 significant gains in terms of exponents. It is also shown that when precoders are used at the transmitter, further exponent gains can be attained at the expense of higher decoding complexity.