  We analyze fading relay networks, where a single-antenna source-destination
terminal pair communicates through a set of half-duplex single-antenna relays
using a two-hop protocol with linear processing at the relay level. A family of
relaying schemes is presented which achieves the entire optimal
diversity-multiplexing (DM) tradeoff curve. As a byproduct of our analysis, it
follows that delay diversity and phase-rolling at the relay level are optimal
with respect to the entire DM-tradeoff curve, provided the delays and the
modulation frequencies, respectively, are chosen appropriately.
