  In this paper, we re-examine the relay channel under the decode-forward (DF)
strategy. Contrary to the established belief that block Markov coding is always
the rate-optimal DF strategy, under certain channel conditions (a link regime),
independent signaling between the source and relay achieves the same
transmission rate without requiring coherent channel phase information.
Further, this independent signaling regime allows the relay to conserve power.
As such, we design a composite DF relaying strategy that achieves the same rate
as block Markov DF but with less required relay power. The finding is
attractive from the link adaptation perspective to adapt relay coding and relay
power according to the link state. We examine this link adaptation in fading
under both perfect channel state information (CSI) and practical CSI, in which
nodes have perfect receive and long-term transmit CSI, and derive the
corresponding relay power savings in both cases. We also derive the outage
probability of the composite relaying scheme which adapts the signaling to the
link regime. Through simulation, we expose a novel trade-off for relay
placement showing that the relay conserves the most power when closer to the
destination but achieves the most rate gain when closer to the source.
