“…However, this sample, small though it is, indicates the amount of effort invested into enhancing the understanding of performance of practical systems over this class of channels where more insight the mere reliable rate is sought. In fact, the results [148], [183], [15], [168], [175] for the error exponent reveal the need for considerable effective time diversity in any practical coding system, which dictates long delays for slow-varying fading models, as to achieve reliable communication in the classical Shannon's sense. The importance of CSI at the transmitter in terms of dramatic increase in the error exponent [31] similar to the capacity versus outage performance [43] also deserves special attention of practical-system designers, and that is opposed to the negligible increase in the ergodic capacity [112] in this setting.…”