Spreading in block-fading channels.

We consider wideband fading channels which are block fading in time and in frequency (doubly block fading). We show that, as bandwidth increases to infinity capacity goes to zero when signaling is constrained in its second moment and peak signal amplitude. This result is consistent with similar results which do not consider doubly block-fading channels. None of these results, however; offer a range for the optimal spreading bandwidth, because they consider only upper bounds to capacity bandwidths is detrimental in terms of capacity, we wish to determine over what range of bandwidths spreading is beneficial. We are able to give a range for the optimal spreading bandwidth by combining our upper bound with a suitable lower bound.