<FONT face=Verdana>In this paper

we first obtain the optimal relay preceding matrix for amplify-and-forward relay system under the requirement of quality-of-service (QoS). Then

in view of the bandwidth limits of the feedback channel in practical communication system

we propose a novel design method of limited feedback relay precoding codebook. Computer simulations indicate that the proposed new limited feedback relay precoding scheme in this paper performs close to the optimal precoding scheme with unlimited feedback

and obtains larger system sum capacity gains and lower biterror rate than that directly based on Grassmannian codebook or random codebook.