Are Yesterday's Information-Theoretic Fading Models and Performance Metrics Adequate for the Analysis of Today's Wireless Systems?

The purpose of this article is to examine some of the models commonly used to represent fading as well as the information-theoretic metrics most commonly used to evaluate performance over those models. We raise the question of whether these models and metrics remain meaningful in light of the advances that wireless systems have undergone over the last two decades. A number of weaknesses are pointed out, and ideas on possible fixes are put forth. Some of the identified weaknesses have to do with models that, over time, have become grossly inadequate. Other weaknesses have to do with changes in the operating conditions of wireless systems, and others with the coarse and asymptotic nature of some of the most popular performance metrics ("diversity" and "multiplexing").