Optimized link adaptation for wireless packet communications based on discrete-rate modulation and coding schemes

Adaptive modulation and coding (AMC) is a powerful technique for improving the spectral efficiency or the error performance in wireless packet networks over fading channels. In this article, using a fixed number of modulation and coding modes we propose a variable power transmission scheme for transmission of packets over block-fading wireless channels. We obtain the general form of optimal power adaptation and optimum AMC mode switching levels that maximize spectral efficiency under prescribed packet error rate (PER) constraint while satisfying an average transmit power constraint. Numerical results reveal that in wireless packet systems with limited packet length, the proposed scheme provides substantial average spectral efficiency gain when compared to the non-adaptive case. The optimization framework presented in this article would be useful for cross-layer optimization of physical layer in packet networks.