This paper, mostly tutorial in nature, deals with the problem ofcharacterizing the capacity of fading channels in the high signal-to-noiseratio (SNR) regime. We focus on the practically relevant noncoherent setting,where neither transmitter nor receiver know the channel realizations, but bothare aware of the channel law. We present, in an intuitive and accessible form,two tools, first proposed by Lapidoth & Moser (2003), of fundamental importanceto high-SNR capacity analysis: the duality approach and the escape-to-infinityproperty of capacity-achieving distributions. Furthermore, we apply these toolsto refine some of the results that appeared previously in the literature and tosimplify the corresponding proofs.
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