Coded Modulation with Mismatched CSIT over Block-Fading Channels

TL;DR

This paper investigates the impact of mismatched CSIT on coded modulation over block-fading channels, deriving outage exponents and demonstrating the benefits of noisy CSIT and advanced precoding techniques at high SNR.

Contribution

It introduces a framework to analyze outage exponents with imperfect CSIT, highlighting the benefits of noisy CSIT and multidimensional precoding in block-fading channels.

Findings

CSIT, even if noisy, improves outage exponents.

Multidimensional precoders enhance outage exponents but increase decoding complexity.

Derived outage exponent as a function of CSIT noise and power constraints.

Abstract

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.