  In this paper, achievable rates and optimal resource allocation strategies
for imperfectly-known fading relay channels are studied. 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
with different degrees of cooperation are considered, and the corresponding
achievable rate expressions are obtained. Three resource allocation problems
are addressed: 1) power allocation between data and training symbols; 2)
time/bandwidth allocation to the relay; 3) power allocation between the source
and relay in the presence of total power constraints. The achievable rate
expressions are employed to identify the optimal resource allocation
strategies. Finally, energy efficiency is investigated by studying the bit
energy requirements in the low-SNR regime.
