Abstract
Link adaptation, in particular adaptive coded
modulation (ACM), is a promising tool for
bandwidth-efficient transmission in a fading environment.
The main motivation behind employing ACM schemes is to
improve the spectral efficiency of wireless communication
systems. In this paper, using a finite number of capacity
achieving component codes, we propose new transmission
schemes employing constant power transmission, as well as
discrete- and continuous-power adaptation, for slowly
varying flat-fading channels. We show that the proposed
transmission schemes can achieve throughputs close to the
Shannon limits of flat-fading channels using only a small
number of codes. Specifically, using a fully discrete
scheme with just four codes, each associated with four
power levels, we achieve a spectral efficiency within
1 dB of the continuous-rate continuous-power
Shannon capacity. Furthermore, when restricted to a fixed
number of codes, the introduction of power adaptation has
significant gains with respect to average spectral
efficiency and probability of no transmission compared to
a constant power scheme.