  In this paper, communication over imperfectly-known fading channels with
different degrees of cooperation is studied. The three-node relay channel is
considered. It is assumed that communication starts with the network training
phase in which the receivers estimate the fading coefficients of their
respective channels. In the data transmission phase, amplify-and-forward and
decode-and-forward relaying schemes are employed. For different cooperation
protocols, achievable rate expressions are obtained. These achievable rate
expressions are then used to find the optimal resource allocation strategies.
In particular, the fraction of total time or bandwidth that needs to be
allocated to the relay for best performance is identified. Under a total power
constraint, optimal allocation of power between the source and relay is
investigated. Finally, bit energy requirements in the low-power regime are
studied.
